Welcome,
I promise to post advice only when I have significant knowledge & experience on the topic. Please don't be offended if you ask me to speculate & I decline. I don't like to guess, wing it or BS on things I don't know. I figure you can wing it without my input, so no reason for me to wing it for you.

A few guidelines I'm asking for this thread:
1. I don't enjoy debating the merits of tuning strategies with anyone that thinks it should be set-up or tuned another way. It's not fun or valuable for me, so I simply don't do it. Please don't get mad if I won't debate with you.

2. If we see it different ... let's just agree to disagree & go run 'em on the track. Arguing on an internet forum just makes us all look stupid. Besides, that's why they make race tracks, have competitions & then declare winners & losers.

3. To my engineering friends ... I promise to use the wrong terms ... or the right terms the wrong way. Please don't have a cow.

4. To my car guy friends ... I promise to communicate as clear as I can in "car guy" terms. Some stuff is just complex or very involved. If I'm not clear ... call me on it.

5. I type so much, so fast, I often misspell or leave out words. Ignore the mistakes if it makes sense. But please bring it up if it doesn't.

6. I want people to ask questions. That's why I'm starting this thread ... so we can discuss & learn. There are no stupid questions, so please don't be embarrassed to ask about anything within the scope of the thread.

7. If I think your questions ... and the answers to them will be valuable to others ... I want to leave it on this thread for all of us to learn from. If your questions get too specific to your car only & I think the conversation won't be of value to others ... I may ask you to start a separate thread where you & I can discuss your car more in-depth.

8. Some people ask me things like "what should I do?" ... and I can't answer that. It's your hot rod. I can tell you what doing "X" or "Y" will do and you can decide what makes sense for you.

9. It's fun for me to share my knowledge & help people improve their cars. It's fun for me to learn stuff. Let's keep this thread fun.

10. As we go along, I may re-read what I wrote ... fix typos ... and occasionally, fix or improve how I stated something. When I do this, I will color that statement red, so it stands out if you re-skim this thread at some time too.

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Let's Clarify the Cars We're Discussing:
We're going to keep the conversation to typical full bodied Track & Road Race cars ... front engine, rear wheel drive ... with a ride height requirement of at least 1.5" or higher. They can be tube chassis or oem bodied cars ... straight axle or IRS ... with or without aero ... and for any purpose that involves road courses or autocross. 

But if the conversation bleeds over into other types of cars too much ... I may suggest we table that conversation. The reason is simple, setting up & tuning these different types of cars ... are well ... different. There are genres of race cars that have such different needs, they don't help the conversation here.

In fact, they cloud the issue many times. If I hear one more time how F1 does XYZ ... in a conversation about full bodied track/race cars with a X" of ride height ... I may shoot someone. Just kidding. I'll have it done. LOL

Singular purpose designed race cars like Formula 1-2-3-4, Formula Ford, F1600, F2000, etc, Indy Cars, IMSA Prototypes, Open Wheel Midgets & Sprint Cars. First, none of them have a body that originated as a production car. Second, they have no ride height rule, so they run almost on the ground & do not travel the suspension very far. Formula 1-2-3-4, Formula Ford, F1600, F2000, etc, Indy Cars, IMSA Prototypes are rear engine. The Open Wheel Midgets & Sprint Cars are front engine & run straight axles in front.

I have a lot of experience with these cars & their suspension & geometry needs are VERY different than full bodied track & road race cars with a significant ride height. All of them have around 60% rear weight bias. That changes the game completely. With these cars we're always hunting for more REAR grip, due to the around 60%+/- rear weight bias.

In all my full bodied track & road race cars experience ... Stock Cars, Road Race GT cars, TA/GT1, etc.  ... with somewhere in the 50%-58% FRONT bias ... we know we can't go any faster through the corners than the front end has grip. So, what we need to do, compared to Formula 1-2-3-4, Formula Ford, F1600, F2000, etc, Indy Cars, IMSA Prototypes, Open Wheel Midgets & Sprint Cars, is very different.

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Before we get started, let's get on the same page with terms & critical concepts.

Shorthand Acronyms
IFT = Inside Front Tire
IRT = Inside Rear Tire
OFT = Outside Front Tire
ORT = Outside Rear Tire
*Inside means the tire on the inside of the corner, regardless of corner direction.
Outside is the tire on the outside of the corner.

LF = Left Front
RF = Right Front
LR = Left Rear
RR = Right Rear
ARB = Anti-Roll Bar (Sway Bar)
FLLD = Front Lateral Load Distribution
RLLD = Rear Lateral Load Distribution
TRS = Total Roll Stiffness
LT = Load Transfer
RA = Roll Angle
RC = Roll Center
CG = Center of Gravity
CL = Centerline
FACL = Front Axle Centerline
RACL = Rear Axle Centerline
UCA = Upper Control Arm
LCA = Lower Control Arm
LBJ = Lower Ball Joint
UBJ = Upper Ball Joint
BJC = Ball Joint Center
IC = Instant Center is the pivot point of a suspension assembly or "Swing Arm"
CL-CL = Distance from centerline of one object to the centerline of the other
KPI = King Pin Inclination, an older term for the angle of the ball joints in relation to the spindle
SAI = Steering Angle Inclination, a modern term for the angle of the ball joints in relation to the spindle


TERMS:
Roll Centers = Cars have two Roll Centers ... one as part of the front suspension & one as part of the rear suspension, that act as pivot points. When the car experiences body roll during cornering ... everything above that pivot point rotates towards the outside of the corner ... and everything below the pivot point rotates the opposite direction, towards the inside of the corner.

Center of Gravity = Calculation of the car's mass to determine where the center is in all 3 planes. When a car is cornering ... the forces that act on the car to make it roll ... act upon the car's Center of Gravity (CG). With typical production cars & "most" race cars, the CG is above the Roll Center ... acting like a lever. The distance between the height of the CG & the height of each Roll Center is called the "Moment Arm." Think of it a lever. The farther apart the CG & Roll Center are ... the more leverage the CG has over the Roll Center to make the car roll.

Instant Center is the point where a real pivot point is, or two theoretical suspension lines come together, creating a pivot arc or swing arm.

Swing Arm is the length of the theoretical arc of a suspension assembly, created by the Instant Center.

Static Camber is the tire angle (as viewed from the front) as the car sits at ride height. Straight up, 90 degrees to the road would be zero Camber. Positive Camber would have the top of tire leaned outward, away from the car. Negative Camber would have the top of tire leaned inward, towards the center of the car.

Camber Gain specifically refers to increasing negative Camber (top of wheel & tire leaning inward, towards the center of the car) as the suspension compresses under braking & cornering.

Total Camber is the combination of Static Camber & Camber Gain ... under braking, in dive with no roll & no steering, as well as the Dynamic Camber with chassis roll & steering.

Dynamic Camber refers to actual angle of the wheel & tire (top relative to bottom) ... compared to the track surface ... whit the suspension in dive, with full chassis roll & a measure of steering. In others, dynamically in the corner entry. For our purposes, we are assuming the car is being driven hard, at its limits, so the suspension compression & chassis/body roll are at their maximum.

Static Caster is the spindle angle (viewed from the side with the wheel off). Straight up, 90 degrees to the road would be zero Caster. Positive Caster would have the top of spindle leaned back toward to cockpit. Negative Caster would have the top of spindle leaned forward towards the front bumper.

Caster Gain is when the Caster angle of the spindle increases (to the positive) as the suspension is compressed, by the upper ball joint migrating backwards and/or the lower ball joint migrating forward ... as the control arms pivot up. This happens when the upper and/or lower control arms are mounted to create Anti-dive. If there is no Anti-dive, there is no Caster Gain. If there is Pro-Dive, there is actually Caster loss.

Anti-Dive is the mechanical leverage to resist or slow compression of the front suspension (to a degree) under braking forces. Anti-dive can be achieved by mounting the upper control arms higher in the front & lower in the rear creating an angled travel. Anti-dive can also be achieved by mounting the lower control arms lower in the front & higher in the rear, creating an angled travel. If both upper & lower control arms were level & parallel, the car would have zero Anti-dive.

Pro-Dive is the opposite of Anti-dive. It is the mechanical leverage to assist or speed up compression of the front suspension (to a degree) under braking forces. Provide is achieved by mounting the upper control arms lower in the front & higher in the rear, creating the opposite angled travel as Anti-Dive. Pro-dive can also be achieved by mounting the lower control arms higher in the front & lower in the rear, creating the opposite angled travel as Anti-Dive.

Split is the measurement difference in two related items. We would say the panhard bar has a 1" split if one side was 10" & the other side 11". If we had 1° of Pro-Dive on one control arm & 2° of Anti-Dive on the other, we would call that a 3° split. If we have 8° of Caster on one side & 8.75° on the other, that is a .75° split.

Scrub Radius = A car's Scrub Radius is the distance from the steering axis line to tread centerline at ground level. It starts by drawing a line through our upper & lower ball joints, to the ground, that is our car's steering axis line. The dimension, at ground level, to the tire tread centerline, is the Scrub Radius. The tire's contact patch farthest from the steering axis loses grip earliest & most during steering. This reduces the tire's grip on tight corners. The largest the Scrub Radius, the more pronounced the loss of grip is on tight corners. Reducing the Scrub Radius during design increases front tire grip on tight corners.

Baseline Target is the package of information about the car, like ride height, dive travel, Roll Angle, CG height, weight, weight bias, tires & wheel specifications, track width, engine power level, estimated downforce, estimated  max corner g-force, etc. We call it "Baseline" ... because it's where we're starting at & "Target" because these key points are the targets we're aiming to achieve. We need to work this package of information prior to chassis & suspension design, or we have no target.

Total Roll Stiffness (aka TRS) is the mathematical calculation of the "roll resistance" built into the car with springs, Sway Bars, Track Width & Roll Centers. Stiffer springs, bigger Sway Bars, higher Roll Centers & wider Track Widths make this number go UP & the Roll Angle of the car to be less. "Total Roll Stiffness" is expressed in foot-pounds per degree of Roll Angle ... and it does guide us on how much the car will roll.

Front Lateral Load Distribution & Rear Lateral Load Distribution (aka FLLD & RLLD):
FLLD/RLLD are stated in percentages, not pounds. The two always add up to 100% as they are comparing front to rear roll resistance split. Knowing the percentages alone, will not provide clarity as to how much the car will roll ... just how the front & rear roll in comparison to each other. If the FLLD % is higher than the RLLD % ... that means the front suspension has a higher resistance to roll than the rear suspension ... and therefore the front of the car runs flatter than the rear of the suspension ... which is the goal.

Roll is the car chassis and body "rolling" on its Roll Axis (side-to-side) in cornering.

Roll Angle is the amount the car "rolls" on its Roll Axis (side-to-side) in cornering, usually expressed in degrees.

Dive is the front suspension compressing under braking forces.

Full Dive is the front suspension compressing to a preset travel target, typically under threshold braking. It is NOT how far it can compress.

Rise = Can refer to either end of the car rising up.

Squat = Refers to the car planting the rear end on launch or under acceleration.

Pitch = Fore & aft body rotation. As when the front end dives & back end rises under braking or when the front end rises & the back end squats under acceleration.

Pitch Angle is the amount the car "rotates" fore & aft under braking or acceleration, usually expressed by engineers in degrees & in inches of rise or dive by Racers.

Diagonal Roll is the combination of pitch & roll. It is a dynamic condition. On corner entry, when the Driver is both braking & turning, front is in dive, the rear may, or may not, have rise & the body/chassis are rolled to the outside of the corner. In this dynamic state the outside front of the car is lowest point & the inside rear of the car is the highest point. 

Track Width is the measurement center to center of the tires' tread, measuring both front or rear tires.

Tread Width is the measurement outside to outside of the tires' tread. (Not sidewall to sidewall)

Tire Width is the measurement outside to outside of the sidewalls. A lot of people get these confused & our conversations get sidelined.

Floating typically means one component is re-engineered into two components that connect, but mount separate.  In rear ends, a "Floater" has hubs that mount & ride on the axle tube ends, but is separate from the axle itself. They connect via couplers.  In brakes, a floating caliper or rotor means it is attached in a way it can still move to some degree.

Decoupled typically means one component is re-engineered into two components that connect, but ACT separately. In suspensions, it typically means one of the two new components perform one function, while the second component performs a different function. 

Spring Rate = Pounds of linear force to compress the spring 1". If a spring is rated at 500# ... it takes 500# to compress it 1"

Spring Force = Total amount of force (weight and/or load transfer) on the spring. If that same 500# spring was compressed 1.5" it would have 750# of force on it.

Sway Bar, Anti-Sway Bar, Anti Roll Bar = All mean the same thing. Kind of like "slim chance" & "fat chance."

Sway Bar Rate = Pounds of torsional force to twist the Sway Bar 1 inch at the link mount on the control arm.

Rate = The rating of a device often expressed in pounds vs distance. A 450# spring takes 900# to compress 2".

Rate = The speed at which something happens, often expressed in time vs distance. 3" per second. 85 mph. * Yup, dual meanings.

Corner Weight = What each, or a particular, corner of the race car weighs when we scale the car with 4 scales. One under each tire.

Weight Bias = Typically compares the front & rear weight bias of the race car on scales. If the front of the car weighs 1650# & the rear weighs 1350# (3000# total) we would say the car has a 55%/45% front bias. Bias can also apply to side to side weights, but not cross weight. If the left side of the car weighs 1560# & the right 1440#, we would say the car has a 52/42 left side bias.

Cross Weight = Sometimes called "cross" for short or wedge in oval track racing. This refers to the comparison of the RF & LR corner weights to the LF & RR corner weights. If the RF & LR corner scale numbers add up to the same as the LF & RR corners, we would say the car has a 50/50 cross weight. In oval track circles, they may say we have zero wedge in the car. If the RF & LR corner scale numbers add up to 1650# & the LF & RR corners add up to 1350#, we would say the car has a 55/45 cross weight. In oval track circles, they may say we have 5% wedge in the car, or refer to the total & say we have 55% wedge in the car.

Grip & Bite = Are my slang terms for tire traction.

Push = Oval track slang for understeer, meaning the front tires have lost grip and the car is going towards the outside of the corner nose first.

Loose = Oval track slang for oversteer meaning the rear tires have lost grip and the car is going towards the outside of the corner tail first.

Tight is the condition before push, when the steering wheel feels "heavy" ... is harder to turn ... but the front tires have not lost grip yet.

Free is the condition before loose, when the steering in the corner is easier because the car has "help" turning with the rear tires in a slight "glide" condition.

Good Grip is another term for "balanced" or "neutral" handling condition ... meaning both the front & rear tires have good traction, neither end is over powering the other & the car is turning well.

Mean = My slang term for a car that is bad fast, suspension is on kill, handling & grip turned up to 11, etc., etc.

Greedy is when we get too mean with something on the car, too aggressive in our setup & it causes problems.

Steering Turn-In is when the Driver initiates steering input turning into the corner.

Steering Unwind is when the Driver initiates steering input out of the corner.

Steering Set is when the Driver holds the steering steady during cornering. This is in between Steering Turn-In & Steering Unwind.

Roll Thru Zone = The section of a corner, typically prior to apex, where the Driver is off the brakes & throttle. The car is just rolling. The start of the Roll Thru Zone is when the Driver releases the brakes 100%. The end of the Roll Thru Zone is when the Driver starts throttle roll on.

TRO/Throttle Roll On is the process of the Driver rolling the throttle open at a controlled rate.

Trail Braking is the process of the Driver braking while turning into the corner. Typically, at the weight & size of the cars we're discussing here ... the Driver starts braking before Steering Turn-In ... and the braking after that is considered Trail Braking. This is the only fast strategy. Driver's that can't or won't trail brake are back markers.

Threshold Braking = The Driver braking as hard as possible without locking any tires, to slow the car as quickly as possible to the target speed for the Roll Thru Zone. Typically done with very late, deep braking to produce the quickest lap times.



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16 CRITICAL RACE CAR DESIGN CONCEPTS:

A.    One of the most important design factors is utilizing all four tires on the track surface for maximum possible adhesion. Shaker Rigs (6, 7 & 8 post rigs) exist to help race car designers, teams & engineers maximize tire contact & loading to the track surface. As a general rule, anything that reduces contact patch and/or tire loading is our enemy & anything that increases contact patch (up to optimum) and/or achieves optimum loading of all four tires is our friend.

B.    Weight is our enemy. Lighter race cars do everything better. They turn better. They accelerate better. They decelerate better. They even crash better (safer). They stress all the components less. Building a lighter car allows us to run less heavy duty, lighter suspension components reducing unsprung & rotating mass ... leading to an even lighter, faster race car. Every ounce matters if you are serious about winning.

C.    Center of Gravity (aka CG ... aka weight mass) matters ... a lot. The mantra of oval track race car builders when it comes to race car weight is "low, light & left." (More left side weight helps cars turning left.) For road race cars it is "low, light & centered." The goal is to have the lightest race car ... weigh the exact same on all four scales ... with the majority of the mass (CG) low in the car & centered in the cockpit.

When the race series or class has a weight minimum, the Racers that build the car as light as practical, then places weight (lead, steel, tungsten) near the center of the car, down low ... will produce a faster, better handling, safer race car.

D.    When we design a race car with a lower center of gravity, it is much easier to drive & can be much faster. A lower center of gravity allows the race car to run flatter through the corners, working all four tires better ... more grip ... more corner speed. A lower center of gravity allows the race car to pitch less (dive & rise) under braking & acceleration, working all four tires better ... more grip ... more corner entry & exit speed. A lower center of gravity makes the race car more stable, higher grip & easier to drive.

E.    If we carelessly design a race car with excessive weight (mass) outside the axle centerlines, we're asking for a scary, ill handling, even dangerous handling, race car. Excess weight ahead of the front axle centerline will make the front end of the car swing out when we exceed total tire grip. Big push (understeer) & then nose hard into the outside barrier.

Similar in the rear. Excess weight behind of the rear axle centerline will make the rear end of the car swing out when we exceed total tire grip. Hard loose condition (oversteer) & then back hard into the outside barrier. Designing the race car with as much of its needed mass inside the axle centerlines is critical.

F.    Track width is CRITICAL. Racing sanctioning bodies know this & enforce track width rules diligently, because all knowledgeable Racers know that even a small increase in track width can provide a significant advantage. Very similar to having a lower center of gravity ... having a wider track width allows the race car to run flatter through the corners, working all four tires better ... more grip ... more corner speed. A wider track width makes the race car more stable, higher grip & easier to drive.

With exception for tight, narrow autocross courses, designing the race car with the widest track width possible is the goal. Widening the car body, or building a wider car body, to achieve the maximum track width is an advantage. A wider track width makes the race car more stable, higher grip, with more corner speed & easier to drive.

G.    With the lowest CG possible, the roll centers also need to be low. Ideally the front roll center is at 0" ground level in full dive at threshold braking. The rear roll center needs to be as low as is practical, while producing a roll axis that is optimum for the particular car to have neutral, balanced, high grip handling through all corners of the course.

H.    Unsprung weight is everything not supported by the springs. In the front this includes half the control arms, tie rods & shocks & all of the tires, wheels, lugs, brake rotors, calipers, mounts, brake shrouds, uprights & hubs ... plus a portion of the brake cooling ducting. If we have IRS in the rear, the list is the same. If we run a straight axle rear, the list includes half the suspension links & shocks & all of the tires, wheels, lugs, brake rotors, caliper, mounts, brake shrouds, rear axle & hubs ... plus a portion of any brake cooling ducting.

Lighter unsprung weight allows the suspension to react & respond quicker to irregular track surface input, providing a higher % of loaded tire contact & grip. Lighter unsprung weight allows the suspension to react & respond quicker to Driver inputs & increases what the Driver feels in the race car.

I.    Of the unsprung weight, the tires, wheels, lugs, brake rotors & hubs are ROTATING WEIGHT. Reducing rotating mass is even more critical than reducing unsprung weight. Accelerating & decelerating a heavier rotating mass take much more time. Said another way, lightening the rotating mass makes the car accelerate & decelerate quicker, producing quicker lap times.

J.    The design structure of every component affects how well that component handles the forces inflicted upon it. The challenge is building lightweight chassis & components without having failures, or reduction in grip due to flex.

K.    The degree of chassis rigidity ... and where it is ... needs to be designed into the car from the start. If a race car chassis is too flexible, the race car will have less grip, be less responsive to tuning changes & have a wider tuning sweet spot. If a race car chassis is too rigid, the race car will have more grip, be more responsive to tuning changes & have a narrower tuning sweet spot.

Race cars that are heavier, more powerful and/or capable of higher cornering g forces ... require more rigidity for optimum track performance. Race cars that are lighter, less powerful and/or capable of lower cornering g forces ... require less rigidity for optimum track performance.

L.    Where the rigidity is designed into the chassis matters as well. Drag cars load the rear suspension significantly more than the front, so the rear of the chassis needs the majority of the chassis rigidity. Road race & oval tracks race cars load the front suspension significantly more than the rear, so the front of the chassis needs the majority of the chassis rigidity. Chassis rigidity designed into the car, needs to be tailored to the direction & location of forces seen dynamically.

M.    Aero drag matters in road racing, but less than you may think. In high powered race cars on road courses, aero downforce is way more important than how much aero drag the race car has. The road race car that has more aero downforce, even with a bit more drag, will be the superior performer. With that said, we don't want unnecessary aero drag.

We want to eliminate & reduce all the aero drag possible, just not to the point of sacrificing aero downforce or track width. Yes, a wider track width & wider front end will create more frontal area & aero drag. The performance advantage of track width trumps aero drag on road courses.

The exception, to these aero rules, is super low powered cars where aero drag is more of a hinderance.

N.    The suspension strategy that includes the target ride height, dive travel (under braking) & roll angle (when cornering) needs to be decided BEFORE the chassis & suspension are designed. There are a variety of reasons why, but the simple ones are ground clearance & camber gain.

If we design an optimal high travel suspension, for example 3"-4" of dive, we may utilize long control arms to slow the camber during dive. This way we can run optimal static camber & achieve the optimal camber gain. If we later decide to run a low travel suspension, for example 1"-1.5" of dive, the long control arms reduce the amount of camber gain can achieve. This problem would require us to run significantly more than optimal static camber, to arrive at the optimal camber. Conversely, we'll have the reverse problem if we start with a low travel design of shorter control arms & decide to run a high travel strategy ... too much camber gain.

On a different note, we may start with a low travel strategy, for example 1"-1.5" of dive, with a 2.5" ride height & later decide we want to run a high travel strategy, for example 3" of dive. The 2.5" ride height back at the firewall isn't the problem. The 2.25" height we designed the FACL crossmember on the front clip is the problem. If we knew we're going higher travel to start, we would raise the front clip (so to speak) in the design phase, so the FACL crossmember allows that travel.

O.    Stiction & friction choices are not often thought about during the design process. But those decisions are often made during design & can be hard to change. Suspension bushings for example. If the chassis & control arms are designed for conventional wide bushings, deciding later to reduce stiction & friction with rod ends can be troublesome. Same with ball joints. Decide this early on.

P.    Safety is often thought of as cage design, seat configuration, harnesses, suits, helmets, HANS & nets. These are all good to decide on beforehand as well, for increased protection in a crash. But spindle, hub & bearing failure cause more crashes than any other part on the car.

Race cars that are heavier, more powerful and/or capable of higher cornering g forces ... create higher load on the critical spindle, hub & bearing components. To PREVENT crashes in the first place, work out the load ratings of our spindle, hub & bearing with a safety factor built in. 

20 CRITICAL HANDLING CONCEPTS:
1.    A car with heavier front weight bias, can go no faster through a corner than the front tires can grip. Balancing the rear tire grip to the front ... for balanced neutral handling ... is relatively easy ... compared to the complexities of optimizing front tire grip.

2.    What we do WITH & TO the TIRES ... are the key to performance. Contact patch is the highest priority, with how we load the tires a close second.

3.    Geometry design, settings & changes to need to focus on how the tires contact the road dynamically & are loaded.

4.    Tires are the only thing that connect the race car to the track surface. Tires play the largest role in race car performance. Rubber in tires hardens rapidly from the day they come out of the mold. Don't run old tires ... unless you want to learn how much it costs to repair race cars. The absolute best performance gain we can make to any race car is fresh, matched tires.

Matching the tires in rubber cure rate, durometer, sizing & sidewall spring rate is key to eliminating handling gremlins that make no sense. The grip level tires are capable of are based on these factors, regardless of tread depth! If the front and/or rear tires aren't matched, we will have different handling issues turning left & right.

5.    After the car is built, tires are selected & the geometry is optimum ... most chassis fine tuning is to control the degree of load transfer to achieve the traction goal & handling balance. Dynamic force (load & load transfer) applied to a tire adds grip to that tire. With the exception of aerodynamics, load transfer from tire(s) to tire(s) is the primary force we have to work with.

6.    The car's Center of Gravity (CG) acts as a lever on the Roll Center ... to load the tires ... separately front & rear. Higher CG's and/or lower RC's increases Roll Angle, but loads the tires more. Lower CG's and/or higher RC's decrease Roll Angle, but load the tires less. Getting the front & rear of the car to roll on an optimum roll axis is desired. Getting them to roll exactly the same is not the goal, because ...

7.    Perpetual goal is to achieve maximum grip & neutral, balanced handling simultaneously through all the corners of the course. To do requires reducing the loading on the inside rear tire (to a degree) ... then increasing the loading of the inside rear tire (to a higher degree) for maximum forward bite on exit. So, on entry & mid-corner, the car needs to roll slightly less in the front to keep both front tires engaged for optimum front end grip, while allowing the car to roll slightly more in the rear to disengage the inside rear tire, to a small degree, to turn better.

For optimal corner exit, the car will have more roll in the front & less in the rear to re-engage the inside rear tire to a higher degree than it was on entry & exit, for maximum forward bite (traction) on exit. This difference is called diagonal roll. This amount differs as speeds & g-forces differ.

8.    Modern day tuners do not use the RC height as the primary means of controlling Roll Angle. We use the suspension tuning items as our priority tools to control Roll Angle. We use the RC priority to load the tires optimally. So, to achieve the optimum balance of Roll Angle & working all four tires optimally ... this all has to work with our suspension ... springs, anti-roll bars & shocks ... and track width ... to end up at the optimum Roll Angle for our car & track application.

9.    Sway Bars primarily control how far the front or rear suspension (and therefore chassis) "rolls" under force, and only secondarily influences the rate of roll. Softer bars allow increased Roll Angle & more load transfer from the inside tires to the outside tires. Stiffer bars reduce Roll Angle, keeping the car flatter & less load transfer from the inside tires to the outside tires.

10.    Springs primarily control how far a suspension corner travels under force, and only secondarily influences the rate of travel. Shocks primarily control the rate of suspension corner travel under force, and only secondarily have influence on how far.

11.    Springs, shocks & sway bars need to work together "as a team." Our springs' primary role is controlling dive & rise, also contribute significantly to the car's roll resistance. Our anti-roll bars (sway bars) primary role is controlling roll, but do contribute minutely to dive & rise. Our shocks primarily role is controlling the RATE of these changes, primarily during race car transitions from Driver input, such as braking throttle & steering. They all affect each other, but choose the right tool for the job & we create a harmonious team.

12.    The front tires need force, from load transfer on corner entry, to provide front tire GRIP. Too little & the car pushes ... too much & the car is loose on entry. The rear tires need force, from load transfer on corner exit, to provide rear tire GRIP. Too little & the car is loose ... too much & the car pushes on exit.

13.    Springs & Sway Bars are agents to load the tires with the force needed to produce maximum grip. Stiffer springs produce the needed force with less travel, whereas softer springs produce the needed force with more travel. Stiffer Sway Bars produce the needed force with less chassis roll, whereas softer Sway Bars produce the needed force with more chassis roll. The tire doesn't care which tool provides the loading force. Ultimately, they combine to produce a wheel load. Our role is to package the right combination for the target dive travel, chassis roll angle & wheel loading we need.

14.    Softer front springs allow more compression travel in dive from braking & therefore a lower CG, more front grip & less rear grip. Stiffer front springs reduce compression travel in dive from braking & therefore a higher CG, less front grip & more rear grip. There are pros, cons & exceptions to these rules.

15.    Too much Roll Angle overworks the outside tires in corners & underworks the inside tires. Too little Roll Angle underworks the outside tires in a corner. Excessive Roll Angle works the outside tires too much ... may provide an "ok" short run set-up ... but will be "knife edgy" to drive on long runs. The tires heat up quicker & go away quicker. If it has way too much Roll Angle ... the car loses grip as the inside tires are not being properly utilized.

16.    Too little Roll Angle produces less than optimum grip. The car feels "skatey" to drive ... like it's "on top of the track." The outside tires are not getting worked enough, therefore not gripping enough. Tires heat up slower & car gets better very slowly over a long run as tires Gain heat.

17.    A lower chassis Roll Angle works both sides of the car's tires "closer to even" ... within the optimum tire heat range ... providing a consistent long run set-up & optimum cornering traction, providing the fastest, most drivable race car.

18.    Higher Roll Angles work better in tight corners but suffer in high speed corners. Lower Roll Angles work better in high speed corners but suffer in tight corners. The goal on a road course with various tight & high speed corners ... is to find the best balance & compromise that produces the quickest lap times. Smart Tuners use Roll Centers & Aero to achieve this.

19.    Tuning is NOT linear two directions with stops at the ends. A car can be loose because it has too little Roll Angle in the rear & is not properly working the outside rear tire. A car can be loose because it has too much Roll Angle in the rear & is not properly working the inside rear tire.

A race car can be pushy because it has too little Roll Angle in the front & is not properly working the outside front tire. A race car can be pushy because it has too much Roll Angle in the front & is not properly working the inside front tire.

20.    Don't forget the role & effects the engine, gears, brakes, Driver & track conditions each have on handling.

Notice: There is overlap in this forum thread from other forum threads
This forum thread is about ALL methods to increase grip. It includes methods covered in front suspension, rear suspension & aerodynamics. There are several areas of important information here, that is not covered elsewhere. You may choose to skip over, of reread, areas you've read before in other topics. Your call.



1.    A-B-A Testing
2.    Mass vs G-Forces
3.    Mass Management
4.    Track Width
5.    Tire Slip Angle
6.    Ackerman
7.    Tires & Wheels
8.    Unsprung Weight
9.    Front Tire Contact Patch
10.    Rear Tire Contact Patch
11.    Spring Rate vs Spring Load
12.    Spring Rate vs Wheel Rate
13.    Tire Loading for Grip
14.    Sway Bar Rate vs Load
15.    High Travel & Low Roll
16.    Modern Spring Materials
17.    Coil Binding Strategy
18.    Energy & Grip Loss
19.    Modern Spring Technology
20.    Bump Stop Technology
21.    Modern Sway Bar Materials – 300M
22.    Stiff Rear Spring Strategy
23.    Dual Spring Strategy
24.    Modern Shocks & Special Valving
25.    Suspension Stiction
26.    Suspension Bind
27.    Chassis Flex
28.    Aero Downforce
29.    Aero Lift
30.    Aero Sideforce


1. A-B-A Testing
I have had a great career in racing. Being able to race on OPM (Other People's Money) was my first goal, but not my top goal, which was/is winning races, if that makes sense. I found winning races attracted sponsors, so winning achieved my top goal while helping me to achieve the other critical goal of funding my racing. Winning 500 races will do that.

Why do I mention this? My key to winning ... my advantage over other competitors ... has been grip. I know grip. I love grip. I think about grip. I dream about the ways of grip. But more importantly, I've tested more ideas for grip than most Racers think about. I've had the luxury of doing over 2500 test & practice days. Typically, "Practice Days" were just working on balancing grip. You can learn about that in the Forum titled "Tuning Techniques for Overall Handling Balance."

Some practice days were challenges of finding grip on new or different track surfaces or conditions. But on my zillion test days, we rented the track to find speed ... through increased grip. My Team & I would take ideas we planned & put them to the test. Some produced big gains. Others small gains. But they all add up. When the gain is small, I like to do A-B-A tests to confirm we didn't get Tricked from track change. If we gained .2 of a second on a road course, to me that's small. If you're not familiar with ABA testing, it goes like this.

A. Run your baseline until you can't go any faster.
B. Change the setup to test & run laps to see the gain or loss.
A. Put the car back to baseline & run laps to confirm the gain or loss.

Then you know. We've had gains so large there was no need to ABA. I'm talking about cutting seconds off of lap times. The story below about Prototype Development Group, a multi-time champion West Coast GT endurance road racing team, we didn't ABA. Instead, I asked them to do full set up & scale on their shocks & springs ... then do full setup & scale on two additional sets of shocks with the same spring brand & rates. That way the ride height, corner weights, spring rates, camber, caster, etc., etc. were identical no matter which shocks they put on. It is well worth a read below.

2. Mass vs G-Forces

Let's talk about weight. Mass. Race car weight & location of that weight. First lighter race cars do everything better. Everything. Betting braking. They can slow down from one speed to another quicker than a heavier car. It's just physics. They can corner at higher speeds. Physics again. They can accelerate out of corners quicker than a heavier car. Yup ... physics.

In race cars, mass and G-forces interact complexly with traction. More mass increases inertia, fighting acceleration and cornering, but also increases the loading on tires, increasing grip. High G-forces, from cornering speed with this mass, are trying to push the race car to the outside of the corner. This same mass (weight) is pushing the tires down harder for more grip. These two forces are fighting each other. We're not trying to defy physics. We can't defy physics. We just need to learn more about physics to create faster race cars than our competitors do.

Two key things to learn. Yes, the heavier race car does create a high level of grip. But it exceeds the tire's optimum slip angle, and therefore grip range, at a lower speed than a lighter race car. When it exceeds the speed of tire grip, the g-forces simply force the car to lose traction & slide outward from the racing line. Whether the front end, or rear end, of the race car breaks traction first, is primarily determined by front/rear weight bias & secondarily determined by handling imbalance due to chassis setup and/or aero.

3. Mass Management

We know, all race cars can exceed the grip of the tires with speed. For heavier race cars that happens at a lower speed than lighter race cars. So, our first goal is to build a light race car. Yes, lighter than the minimum weight rules of whatever series we're running. This is so we can place the ballast where we want for optimum handling. In oval track racing, winning chassis builders have a common mantra ... "Low, Light & Left." Meaning they want to build their race cars with the weight low as possible, as light as possible & with the ballast & weight bias to the left as much as possible. Remember they're turning left.



In road racing the mantra is "Low, Light & Centered." Meaning we want to build our race cars with the weight low as possible, as light as possible & with the ballast & weight bias centered as much as possible. Ideally, we want all 4 scales to read the same. 50/50 front & rear. 50/50 left & right. With driver & all weight to race. We also want to move any weight possible from outside the axle centerlines to in between the axle centerlines.

This is to help our polar moment of inertia. If there are seriously heavy masses ahead of the FACL, when the race car loses grip, the front end will jump quickly to the outside of the corner. If there are seriously heavy masses behind the RACL, when the race car loses grip, the rear end will step out quickly, even violently, to the outside of the corner. Let's hope there are not cars, walls or objects there.

Building your race car with the engine & trans moved rearward from the FACL is key to achieving this 50/50 F/R weight bias. Many series are ran by racers that know how much advantage this is, and don't allow it. They regulate the engine (and sometimes transmission) location. SCCA GT classes & Trans Am typically have a "#1 spark plug at the FACL" rule. I suggest you build it to the rules limit.

But if your building a track car or racing in series that don't regulate engine & transmission location, I strongly urge you to build your car with significant setback. NASA has a "keep the firewall in the stock location" rule for American Iron & AIX. But most other NASA road racing, endurance racing & time trial classes have no engine location or firewall rules.

Same for all the similar road race & time trial groups like COM, NE GT & EMRA. SCCA regional racing almost always has open rule classes like SPO & SPU. Endurance road racing series WRL (World Racing League) & USTCC (United States Touring Car Championship) also have no engine location or firewall rules. In Australia & New Zealand there are more series with no engine location or firewall rules, then series with. In UK club racing, they don't care either. Same with time attack series. No engine location or firewall rules in the upper classes.

When we talk front to rear weight bias ... we initially are talking static. Then, under braking, the decel g-forces (negative g-forces) are transferring "load" from the rear tires to the front tires. But that doesn't mean the car's static weight is thrown out
the handling window. Quite the contrary ... when the car is braking, cornering & accelerating at its limits ... as race cars and track cars should be. You can't simply brake harder and shift the weight balance of the car farther. You're already at the limits ... and so is load transfer.

The static weight balance affects the car in two major ways. The first is, the more weight you start with in the front, the more grip the front will have "initially" and up to the limits of grip. The more weight you start with in the rear, the more grip the rear will have
"initially" and up to the limits of grip. As you brake, corner & accelerate, you are transferring load ... but it is a percentage of the car's weight ... based on g-forces.

As a braking example:
A. If you have 50% weight up front ... and you pull X.xx g-forces under braking & transfer 35% of the car's weight in load transfer ... the front tires are seeing 85% and working hard, but optimally right at their limit. The rear tires are seeing 15% ... still have enough load for some grip ... and are helping to brake & slow the car to a much lesser degree than the fronts.

B. If the same car had 60% weight up front ... and you pull the same X.xx g-forces under braking & transfer the same 35% of the car's weight in load transfer ... the front tires with 95% of the load will become overloaded and push. That is ... if the rear tires with only 5% load don't get so light they lose traction & become loose first.

Having aero downforce comes into play, but doesn't change this in ways you may think. First, let's embrace that we need the car to be aero balanced. That doesn't automatically mean we're getting the same amount of downforce front & rear ... but it does mean we're getting downforce in the appropriate amounts front & rear ... to have the car handle balanced or neutral.

Assuming the car handles balanced & neutral ... and we have significant downforce front & rear ... we can drive the car in deeper, brake later & harder ... and have the added grip to stick. But the concepts in examples A & B above still apply. We're deeper in the corner ... we're pulling higher negative G's ... but the same concepts apply. Aerodynamics aids help increase traction, but they don't change the laws of physics, inertia, load transfer, etc.

Make sense?



The second major way a car's weight balance comes into play ... is the mass location of a race car affects the polar moment of inertia in yaw. If we have a car with 60% static front weight ... that extra weight (from gravity) loads the front tires more, giving them more grip up to a point.

That point is when the lateral g-forces from cornering speed ... exceeds the cars grip capacity ... and the car breaks free. Assuming we have the car's handling "balanced" and "neutral" ... the front of the car with 60% of the car's weight has more inertia ... and therefore, when the driver tries to carry higher cornering speed ... and exceeds the tires limits of traction ... it is the front end that will break free first and hardest. (Pushing) This is why front heavy production cars "push" when driven past their traction limits.

Lastly, but most important, is to get the mass of your race looooow. Everyone knows the center of this mass is calles the Center of Gravity, often shortened to CG. The lower the CG is, versus the track width plays the BIGGEST role in how fast a race car can corner. It is the most important thing. Of course we want to build the race car to sit low. As low as rules allow if racing. Track car racers tend to run higher ride heights for a variety of practical reasons. From not scraping in the pits to loading on the trailer easier. But just as important as ride height, is to mount EVERYTHING in the car as low as possible.

Mounting the engine & transmission low is the most common. I highly recommend we mount these as low you can afford to. Afford? Yes. We don't want to knock the oil pan off the race car in any off track excursions (aka "farming"). If your budget requires a wet sump engine, we're going to mount it higher, so the pan is not below the front frame clip (crossmember).

Obviously, if you can afford a dry sump, for Pete's sake run one. Your engine will last longer & with a thinner oil pan, we can mount the engine & transmission much lower. So low in fact, you may need to modify your bellhousing bottom & run a smaller diameter flywheel. The lower the mass, the more grip & corner speed we'll have.

In addition, we should look at ALL the weight. Get it low. Why is your dry sump tank so high? Mount it just low enough it is safe. Battery? Mount it low. In our Track-Warriors & Race-Warriors that achieve equal weights on all 4 corner scales ... we mount the dry sump tank on the far right passenger side & low. We mount the battery behind the main hoop, far right & low in front of the right rear tire. We mount the fire extinguisher canister in the cockpit, just ahead of the main hoop, far right & low. Exhaust? Far Right & low. Engine management ECU & data logger? Far Right & low. Fuel Cell? A couple inches to the right, but low, and as far forward as possible.

As far as the fuel cell goes, most series have an either or rule. Either the bottom of the fuel cell needs to be a minum of 6" above ground, or at least not below the frame rails. This is another reason we run "underslung" frame rails in all of our Race-Warriors. So we can get the fuel cell lower.

EVERYTHING MATTERS! Again, the lower the mass, the more grip & corner speed we'll have.

4. Track Width
Just as important as getting the mass low, is achieving the maximum track width. Remember the physics. It's not CG alone. It's the relationship of the CG to the track width. The lower the CG is relative to the track width, the more grip we'll have & the faster the car can corner. Said another way, for clarity, the wider the track width relative to the CG, the more grip we'll have & the faster the car can corner.



All savvy racers know this of course. So in most rule driven road race series like SCCA GT classes, Trans Am (all classes) & NASA American Iron (AIX too), they have track width or body width rules. If they only have body width rules, read the rule book thoroughly & you'll find they have a rule the tires can not extend past the body. Whatever the rule is ... if you're racing to win ... push the rule right up to the limit. I assure you that your competitors are. See image below that shows TA2 rules limiting body width.



Most NASA road racing, endurance racing & time trial classes have no track width rule. Same for all the similar road race & time trial groups like COM, NE GT & EMRA. SCCA regional racing almost always has open rule classes like SPO & SPU. Endurance road racing series WRL (World Racing League) & USTCC (United States Touring Car Championship) also have no track width rule. In Australia & New Zealand there are more series with no track width rules, then series with. In UK club racing, they don't care either. Same with time attack series. No track width rule in the upper classes.

So? How fast do you want to safely go in your track car or low rule road race car? My friend Randy Chastain built the infamous 70 Mustang that was 6" wider than normal. That is a huge advantage. If you're buying a composite race body, or having a hand built steel race car body made, just remember how important track width really is. If you're working with a steel or composite body of OEM dimensions, can you widen it? Sure you can. Lots of ways. Wide body kits. Widening the factory fenders & quarters. Flares, etc.

The only thing I get concerned with when adding flares, is to not do them so close to the tire that you limit travel. Remember, we want to get the dynamic front CG as low as possible under braking & cornering. The outer edge can be close, Just don't make the angle of the flare too tight to the top of the tire. Of course camber gain will help clear the flare (or fender). I suggest building your flares AFTER you have the suspension working & can run it through it's motions, with steering.

5. Tire Slip Angle

Understanding tire loading & slip angle:
My father used to say, "If you're going to play with Rattlesnakes ... you need to know what rattlesnakes do."  He also taught me the concept of seeking out mentors, becoming a student of the things I care enough about to be good at & that nothing beats hands on experience, learning alongside masters of the craft. I agree.



If you're going racing, and you don't understand tires, you're already beat. If you don't learn about tire slip angles & how they affect grip, you will have a hard time winning consistently. This is a key fundamental of making race cars have grip & go fast.

Slip Angle Primer:
Tire grip and slip angle coexist. The tire actually doesn't have grip unless it has slip angle ... and it doesn't achieve any slip angle without grip. I know that sounds weird. Just accept that the tire has to have side load before it truly creates grip. Just like your significant other has to be happy before you're getting ... ah ... never mind.

If you & I were in the tire designing or development business, we would need to understand this in much more depth. But we're not. We're going to buy "off the shelf" tires & tune our cars around them the best we can. Knowing the basics of how tire design affects slip angle ... and what slip angle is ... will help you to become a better tuner. We'll start with what slip angle is ... how this affects your tuning ... and how tires differ.

I have found discussing "squirm" first ... then rear tire slip angle ... front tire slip next ... and inside front tire slip angle last ... makes the whole process easier to understand. Just like my normal "peeling the onion" process of explaining things.

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Squirm happens:
Squirm is the flexing of the rubber that makes up the contact patch. Don't confuse this with sidewall flex. Squirm is the tread flexing within itself. Squirm is an unfortunate characteristic of rubber tires, so more is bad & less is better.

Racing slicks have squirm, but very little, because the contact patch is one big surface ... like a wide but thin chunk of rubber. If the slick has a thick tread depth, more squirm will happen as this taller block of rubber flexes more under load. As the racing slick wears down during a race & the tread is thinner, squirm decreases.



Street tires have significantly more squirm, because the tire contact patch is "cut" into tread blocks (or runners). The grooves around the tread blocks allow the tread blocks to squirm more. The larger the tread blocks, like the DOT competition tires have, the less squirm. The smaller the tread blocks (width or length) like with everyday passenger car tires ... the more that tread will squirm ... especially when the tread blocks are new & "tall".

This is why street tires usually achieve their best dry grip just before they wear out, unless they've gotten hard from age or sunlight. I'm sure most car guys know rubber hardens over time, faster in sunlight. As rubber hardens its coefficient of friction is reduced, therefore grip diminishes. You can tune around old, harder tires, but you can't make them fast.

Radials have less squirm than bias ply tires. The significantly stronger structure the radial belted tire offers reduces tread squirm in street tires & racing slicks. This stronger, radial belted structure also increases the sidewall strength & sidewall spring rate. Radials achieve more grip with same size of contact patch & same rubber compound, but the slip angle "happy window" gets narrower.

To reduce squirm while still utilizing the freshest rubber, some competitors have new tires shaved to half depth, or a specific depth they determined offers optimum performance. Some racers utilizing DOT race/street tires shave the tires to prevent overheating the tread blocks. Some tire manufacturers of DOT competition tires are producing tire new with shallower tread depths, so they don't need to be shaved. Obviously smaller tread blocks get hotter, quicker, if the tread compound is soft. That's one of the reasons the new DOT competition tires have such large tread blocks ... to keep the tire cooler ... along with adding more contact patch surface area.

You can tell when a DOT competition tire is being severely overheated because the tread blocks will blister or chunk ... the edges will tear or chunk ... and the surfaces get a bluing haze. Squirm build heat, so shaving the tires helps reduce heat buildup & helps keep a DOT race/street tire in its temperature happy window.

Larger scrub radius creates more tire squirm. The tire tread is trying to pivot around the higher scrub radius ... which literally torques the tread around a radius. Versus pivoting the tread in the center, which is what a zero scrub radius achieves. The larger the scrub radius, the more the tire will lose traction as it is being turned, because of increased squirm.

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Slip Angle:
Slip angle is the difference in angle of the wheel ... relative to the tire's contact patch ... which is distorted due to cornering forces. Regardless of what's inside the rubber ... tires are still rubber. They flex & spring back. The tires sidewall, carcass & tread all distort ... as the g forces are pushing the car towards the outside of the corner ... and the tire is "sticking" to the track. The tire's contact patch actually twists ... and points to the outside of the corner slightly. The "angle" part of slip angle ... is the difference in angle of the wheel itself & the direction of the contact patch ... stated in degrees. I think this illustration shows it best.



The tire in the image above could be any of the four tires ... on the car in a left hand turn. All four tires will have the slip angle the same direction, but often not the same slip angles. During cornering the outer tires are typically going to achieve a higher slip angle due to more load. The inside tires are at a lower dynamic slip angle than the outside tires, because they have less load on them. The g forces cause the majority of the tire to be pulled outward with the car & wheel. But the contact patch ... with traction ... stays connected to the track ... and is twisted toward the outside of the corner.

Braking & acceleration also cause weight transfer through g-forces. When the car is braking ... the front tires will have a higher slip angle than the rear. The higher the braking forces are ... the higher the slip angle split is from front to rear. Acceleration transfers weight to the rear tires ... from the front tires ... achieving the reverse slip angle split, but typically not as much.

Let's start with rear tires & wheels first ...
If the contact patch on the tire in the illustration above ... is angled 7° outward ... from the rear wheel angle (which should be parallel to the car) ... we would say the tire has a 7° slip angle. That may ... or may not be at the tire's optimum point of grip. Every tire is different, with tire design, compound, sidewall construction, sidewall height, wheel width-to-tire width ratio, tread type & depth all playing a role in what the "Slip Angle Graph" looks like for any given tire.

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Types of Tires & Their Slip Angle Curves:
Most series in the lower levels of oval track racing run on bias ply racing slicks. IMSA, Trans Am, Indy, ARCA & all the top series of NASCAR, run radial racing slicks. The bias ply tires are more forgiving. A good driver can really feel "the fast zone" of a bias ply slick ... and drives it up to the edge of that feel constantly to win races. If they go past that edge with bias ply tires, the car loses grip, but it's not so abrupt. The radials slicks have substantially more grip ... until they don't. When the driver goes past that edge with radial slicks, the car loses grip abruptly.

Take the "passenger car tire" graph with a grain of salt, this graph is older & the new low tread wear, ultra-high performance summer tires & "DOT legal" race inspired tires have shorter, stiffer sidewalls than the "passenger car tire" shown in this graph. This is going to make the optimum slip angle lower, the sweet spot narrower & fall off more abrupt ... than the "passenger car tire" shown in the green line. I believe the low tread wear & DOT legal competition tires will be somewhere in between the red & green lines ... but closer the red line, with lower CoF & slightly higher optimum slip angle.

When a tire breaks traction ... and starts sliding on the track ... the slip angle reduces but doesn't go to zero as some people believe. There is still friction between the track surface & tire contact patch (unless the tires are airborne or on a liquid with no friction qualities) so the tires still have "some" slip angle ... but the car is traveling faster than that smaller slip angle can provide grip. As the car's speed gradually comes down ... assuming there is enough track run off area ... at some point the speed will come down & meet the up with the tires' available grip of the lower slip angle ... and regain traction.

Drivers say stuff like, "The car scrubbed off enough speed that the tires caught ... and I kept going." Hopefully this happens before the car impacts objects like concrete walls, barriers, other cars, cows, etc.

The tire graph says it all. Look at the Slip Angle graph. The blue line is the racing radial slick. You can see it has more grip ... and how narrow the "sweet spot" is ... then how sharply it falls off when over driven. The red line is the bias ply slick ... much more forgiving ... but less grip.


 
Slip Angle graph above comparing radial slicks, bias ply slicks & passenger car tires
 
As an example, for discussion only, let's say we have a sample rear tire with the "optimum" slip angle of 6° ... and maintains the same high level of traction up to 6.5° of slip angle. We would call this 6° to 6.5° range the tire's "happy window" or "sweet spot." In this example let's say grip starts to fall off past 6.5° of slip angle and loses grip fast at 7° & beyond. We would call this 6.5° to 7° window the "safety net" zone. Anything past 10° (in this example) is in the "hang on for dear life" zone.

As the car is driven faster through the same corners ... and the g forces increase ... the slip angle will increase too. When the rear tires are gripping at their absolute limit ... with a corner speed of 86.45 mph ... the rear tires are at the limit of the slip angle happy window. On the next lap if you try to go "a tick" faster than 86.45 mph in the same corner ... the increased g forces will take the slip angle past the tire's slip angle happy widow ... into the "safety net" zone. A really good driver feels this ... feels the car sliding slightly more than normal ... drives through it ... and knows to back it down "a tick" the next time through this corner.

The size of the "safety net" zone is dependent on the tire's slip angle curve. A more forgiving tire may allow the driver to have overdrive the car more & still saved it. A less forgiving tire would cause the tires to break traction abruptly ... and be harder if not impossible to "save." In my driver development program we taught our drivers how to find the limits of braking, turning & accelerating. How the tire feels in the safe, optimum & safety net zones ... and how to keep the tires in their optimum zone for the full traction circle. Maybe I'll do a book and/or workshop on that for the PT crowd someday.

As the driver carries more & more speed through this corner, the slip angle of the rear tires increase. As the driver gets the car to carry corner speed near the limit of grip ... the g-forces from this speed have increased ... so the slip angle of the tire is higher & so is the tire's CoF (Grip). Said another way ... in my attempt to provide clarity ... the tire's CoF & grip increase with slip angle ... caused by the increased speed's higher g-forces. If the driver gets the car's cornering speed "to the limit" of adhesion ... in this example the tire would have 9° of slip angle.

If you are serious about competing at high levels there are some key things to know:
• The optimum slip angle has a feel.
• Each side of the optimum slip angle has a different feel.
• Great drivers learn all three feels.
• Great drivers know the "safe feel" before optimum slip angle, and push beyond it.
• Optimum slip angle is approximately 2% beyond "safe grip" and is therefore sliding the car to very small degree.
• Great drivers master the feel of optimum slip angle & drive to keep the tires & car at this point.
• There is a window of lower CoF & grip just past the optimum slip angle & it has its own feel.
• This "safety net" window varies greatly with tire design, but higher grip tires typically have smaller safety nets.
• This "safety net" zone is still quick, but not optimum ... and leads to excessive tire heating & tire wear.
• At the very top of professional racing, that safety net is razor thin.
• Great drivers learn the feel of this "safety net" window, however small ... and drive to keep the tires out of this area.
• Drivers changing to a race series switching from bias ply slicks to radial slicks say the tires are the biggest learning curve.

Getting the outside rear tire in each corner to optimum slip angle is primarily "a driver thang."
On any particular corner, the driver's role is to push the envelope a little more each lap, until they find the limits of traction. The optimum traction for the outside rear tire is the optimum slip angle.

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Rear Steer:
Slip angle in the rear tires creates rear steer. The contact patch of both rear tires end up pointed to the outside of the corner. This helps the car to turn. Thank goodness. Because the slip angles in the front provide counter steer, making it harder to turn.

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Tuning for optimum rear tire slip angle:
"Most" tuning to achieve optimum slip angle for the rear tires ... to increase grip in the rear of the car ... is for the rear tire on the inside of the corner. The inside rear tire is at "less than optimum slip angle" ... because it is being worked less, due to the car's roll angle. The flatter the car corners ... working the inside tire more ... makes the inside tire's slip angle increase ... increasing the inside tires CoF & grip ... therefore making the rear of the car capable of carrying more corner speed.

If you get the car rocket fast, running super low roll angle, with optimum rear traction, the outside tire will still have a higher slip angle & therefore higher CoF & grip. Just the way it is. For road racing & AutoX ... this is our stopping point. The rear tires will have a "slip angle split" (difference). We can't drive the car any faster ... in an attempt to increase the slip angle of the inside rear tire ... without taking the outside tire out of its slip angle "happy window."

In oval track racing, we have a trick where we toe out the right rear tire & wheel. We are basically creating "toe out" with the rear tires. This does two very important things. One is ... it decreases the slip angle of the outside tire ... without affecting the slip angle of inside tire. Now the rear of the car can be driven faster before the outside rear tire reaches its optimum slip angle. The inside rear tire will now have more slip angle due to the increase in corner speed & g-forces ... and a higher CoF & Grip because of it . While it's not exactly a 1-to-1 ratio ... if we toe out the right rear tire on an oval track car by 2° ... and drive the car at the limits of the of the right rear tire ... we will get close to 2° increase in the left rear tire's slip angle. This increases the grip of the left rear tire ... increasing the overall grip in the rear of the car.

And ... with the right rear tire's slip angle pointing outward 2° more ... and the inside rear tire's slip angle pointing close to 2° more outward ... the car is constantly turning, but with grip. This helps these beasts turn better in the corners. NASCAR had to step in and limit the amount, as teams were taking this concept to extremes. The cars can still be seen "crab walking" down the straights, but it's less noticeable than before the 2° limit rule.

Someone mentioned that Herb Adams (I loved his book as a young racer) suggested having the rear end toed in decades ago in his book. Tires had much taller sidewalls back then & were not very responsive. Toeing in the rear tires, gets the outside rear tire to its slip angle quicker ... giving the outside rear tire grip "sooner" on corner entry.

I can only assume Herb suggested this to make the car more responsive. A LOT of road racers with IRS run toe-in in the rear. It provides them rear grip sooner on turn in. But it does limit the rear tires maximum speed capabilities. I do add rear toe-in with IRS rear suspension if the driver is a rookie or it's a track car. That's for safety, not speed. If the driver is experienced or a pro, I do not run toe-in on IRS. The car will be faster without it.

Herb also suggests negative camber in the rear end, which in small amounts can still make sense today. Remember camber helps the tire on the outside of the corner to have a better contact patch ... while hurting the inside tire, making its contact patch worse. So, the primary reason to do so would be more even and/or prolonged tire wear. I only use camber in the rear end, with very good front suspension geometry.

Because with a tunable rear suspension, we can typically get more rear tire grip than we can use when running average front suspension geometry. We're still limited by the front tire traction level. After we get ALL the front grip we can get ... we're tuning the rear suspension to end up with a balanced, neutral handling car. If we have a bad ass race car with really good front end geometry & front grip, I find I need the cambered rear end to keep up & be balanced.






Outside Front Tire:
Assuming the driver is getting the car to go where they intend ... meaning the car is not pushing or loose ... the car is neutral ... the slip angle of the outside front tire is the actual path of the car's front end.

Read that again. This is important.

If the wheels are turned 20° to the left and the slip angle is 7° to the right ... the actual trajectory of the front end of the car is at 13°. Just as the slip angle in the rear tires add steering effect ... the slip angle in the front tires add counter steering effect. Thank goodness the rear steer effect is helping the car to turn. As long as the front & rear slip angles are the same ... the tires opposing angles will balance out each other ... to produce a neutral steering effect.

Toe does not matter to the outside front tire. The slip angle of the outside front tire is the actual path of the car's front end. So, there is nothing to "tune" for to achieve optimum slip angle on the outside front tire. The optimum traction for the outside front tire is the optimum slip angle. If we exceed the optimum slip angle for the car ... either through speed & g-forces, too much steering angle or a combination of both ... the outside front tire will lose grip ... and bye bye ... the front end is washing to the outside of the track.

Again, it's the driver's role to push the envelope a little more each lap, until they find the limits of traction ... and if the front or rear exceeds its capabilities first ... then tune from there.

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Inside Front Tire:
Now, this is where we get into tuning for tire slip angle. This is where we can have an effect that increases overall front tire grip. And because the car can go no faster through a corner than the front tires can grip ... as we increase front tire grip ... we are increasing the corner speed capabilities of the whole car. As we add front end grip ... adding more rear tire grip to keep the car balanced & neutral ... is relatively easy.

This is where & why ... toe & Ackerman ... are used in the front end of race cars. Read that again. This is key. Toe & Ackerman are ONLY used in race cars to help the inside front tire achieve the optimum slip angle. Period.

In the rear of road race, track & autocross cars, we often end up with the inside rear tire having less than optimum slip angle ... and therefore less than optimum CoF & grip. No biggie. The rear of the car is easy to get grip in. But the front ... whew! The front is challenging. The good news is ... in the front end ... we can use toe & Ackerman to achieve the optimum slip angle for the inside tire ... thereby increasing the overall grip of the front end.

The following strategy assumes we are running the car relatively low roll angle, so we can keep some load on the inside front tire when cornering. Pro setups run roll angles around 0.5° to keep the inside front tire loaded the most. Track autocross cars that run 1.0° to 1.5° are keeping some load on the inside front tire, just not as much. How much load the inside front tire sees, affects how much Ackerman it will require to achieve the optimum slip angle & maximum grip.

Lower roll angles, like pro race setups around 0.5°, need less Ackerman. Higher roll angles, like 1.0° to 1.5°, require more Ackerman. Somewhere in the 2.5° & higher roll angles, Ackerman doesn't matter at all, because we're not keeping any load on the inside front tire. No load equals no grip, regardless of what we do the geometry, alignment & steering.

The concept is pretty simple once we understand we need both front tires at their optimum slip angle. Remember, the outside front tire is at the optimum slip angle, and 100% of its possible grip, assuming the driver is pushing the car to its limits & the car is balanced.

But, because the inside front tire is loaded significantly less than the outside front tire ... the inside front tire is NOT at its the optimum slip angle, if both steering angles match. Therefore, the inside front tire is not achieving its full grip potential. That potential will never be as much as the outside front tire, but it is proven possible to achieve 15%-25%. In case that's not clear, a race car with 15-25% more total front grip will out corner all other cars not working the inside tire optimally ... by a lot. If we're giving up 15-25% more total front grip, we're getting our ass kicked.

If we can mechanically turn the inside tire to a higher degree than the outside tire ... to achieve optimum slip angle ... we will increase the grip of the inside front tire. Our tools are toe, Ackerman and bump steer. Don't over complicate this. Let's discuss them one at a time.

6. Ackerman
As most Racers know, the Ackerman effect gets the inside front tire to turn more than the outside front tire ... through steering geometry. It can be measured in fractions of an inch or in degrees ... and to be consistent if we're tuning with Ackerman ... needs to be set & checked at the same steering
angle every time. Some use 20° steering angle ... others 15°. I use 15°, since in my experience we rarely see over 15°.

When working with toe, Ackerman and bump steer, I prioritize Ackerman, because the Ackerman works at any suspension position ... from ride height to fully compressed in dive. I design in a certain amount of Ackerman ... to compliment the Static Toe-Out setting ... for a combined total dynamic toe setting ... with the goal of achieving the optimum slip angle on the inside front tire. If I cannot achieve that goal with Ackerman & Toe-Out alone, then I will add in "Bump Out" in the bump steer, until I achieve optimum slip angle for the inside front tire.

Bump Out is a slang term combining bump steer & toe out. We typically want Bump Out in dive (compression) only. If I said the car has 1/8" of Bump Out, I mean at target dive, the steering adds 1/8" of total toe-out. I have seen winning autocross cars run over 1" of bump out, because the car turned so much better & they did not have much Ackerman. I prefer to design in Ackerman, to utilize lower amounts of Bump Out.

Ackerman Only:
Some Racers want to use Ackerman only to achieve Toe-Out in the corner. And while we can achieve the proper Toe-Out for optimum slip angle of the inside front tire when the steering is fully turned in the corner ... the front end is not very responsive at initial corner turn in with zero toe. There are some
exceptions ... super high speed tracks where corner entry speeds are ultra-high.

Toe-Out:
Toe-out ... meaning the front of tires are pointed out ... is a staple of short track, road racing & AutoX. And for several good reasons. Toe-out is one "easy to use" & "easy to measure" tool to get the inside front tire turned more than the outside front tire. For decades ... Racers that understood slip angle and those who didn't ... knew if they added Toe-Out ... up to a point ... the car turned better.



Another plus of Toe-Out ... is improved steering response not achieved with Ackerman. When the driver first turns the steering wheel ... especially at low steering angles ... Toe-Out really helps the car be responsive. We want to run enough Toe-Out to improve initial corner turn in (responsiveness) ... without using so much Toe-Out that it causes "scrub" problems as the car drags the tires down the straights. For most road course, short track ovals & AutoX ... I find 1/8" total Toe-Out to be a pretty good baseline to start with ... 1/16" total for really fast road courses with primarily 100+mph high speed corners ... and zero toe on big oval super speedways with 160+mph corners

Toe-Out Only:
In many cases ... just using Toe-Out isn't enough to achieve optimum slip angle for the inside front tire. We don't want to cause scrub problems. So, run just enough Toe-Out for good corner turn-in responsiveness ... and get the rest of the slip angle needed with Ackerman, bump steer or a combination of both.

Bump Steer:
Most standard production car bump steer is ugly ... putting the front end into a toe-in condition as the suspension compresses ... making the car push. This has been the goal of automotive engineers to "protect the driving public" from themselves. When we "bump steer" a performance or track car ... the
typical assumption is to achieve zero bump steer through the usable suspension travel of the car ... or as close to zero as we can achieve. Most tuners build in a small, measured amount of "Bump Out" into the set-up ... getting the steering to slightly Toe-Out as the suspension compresses, like I do.



The thought is ... and it is mostly correct for race cars ... that the car is never going to turn on the track without the suspension compressed. So, the strategy is simple ... set the bump steer so the front end Bump Out ... to a target Toe-Out number ... as it compresses the suspension to X.xx suspension travel.

A concern is the driver braking softer or harder in different corners. With my drivers, I'm coaching them on why & how to adjust their brake points, pressures & braking durations to "load the front end" the same, in every corner. The bigger concern is on long, fast sweepers ... and some esses ... we're not using the brakes at all.

"Dynamic toe" is the combination of our static Toe-Out ... plus any Bump Out ... and Ackerman. This is the effective Toe-Out achieved (hopefully) with the suspension compressed, body rolled & the steering turned ... as it actually does in the corner. Many Racers, myself included, refer to this as Ackerman. Technically, it is the combination of Toe, Bump & Ackerman. So just get clarity, if we're not. We can achieve the optimum slip angle for the inside tire ... by tuning on a combination of these tools ... to end up with correct dynamic toe setting.



How do we know if we're working the inside tire more?
The whole tire surface heats up. Not an edge ... the whole tire. If I'm road racing, I like to look at the infrared temp sensors pointing at the tires. If we don't run data acquisition, a low buck way is to go find & run a skid pad with a good tire temp gauge in hand. As we are only going one direction ... then
stop & take temps ... we can really see what we're doing with the inside tire compared to the outside tire. I've taken this so far the inside tire runs hotter than the outside tire, which is not optimum either.

Anti-Ackerman:
They always say there is an exception for every rule. In some formula car series, which are NOT our focus here, the cars run super low Roll Angles, with tires that operate with much lower slip angles, they need to run anti-Ackerman. They don't want to reduce their Static Toe-Out, because that would reduce their initial corner turn in responsiveness. But the Toe-Out causes their inside front tires to have too much slip angle ... which reduces grip ... and over heats the tires. So, they keep their Toe-Out ... and set up the steering geometry to achieve an anti-Ackerman affect ... to the point that optimizes their tires' slip angle.

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Other Tire Slip Angle Notes:
We don't need to know anything about slip angle to get a car to turn. There is no "steering angle" gauge in the cockpit. Could we imagine if there was? Ha-ha. I can see some race driver talking to his crew chief, "Dang it Jim, I have the steering turned to 15° but the car isn't turning in a 15° radius."

Frankly, we don't need to know the optimum slip angle number for our tires to tune our track car to its optimum. Regardless of whether the optimum slip angle is 5° or 10° ... we're going to tune the front & rear suspensions for optimum grip. Understanding slip angle concepts make us better informed, smarter tuners. But knowing the specific slip angle number doesn't change our strategies or our tuning.

Converting toe to degrees is easy with an angle calculator. If we use a common set of 23-1/2" long toe plates ... the two tape measures rest at 22" ...
making this chart helpful:
.375" (fat 3/8") = 1.0 full degree
.250 (1/4") = .65 of a degree
.125" (1/8") = .325 of a degree
.0625 (1/16") = .163 of a degree

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Tire Slip Angle vs Car Slip Angle:
If one end of the car is traveling a direction other than the contact patch slip angle is pointing ... then we have a car slip angle. If this is in the rear end, we call it loose or oversteer. If this is in the front end, we call it pushing or understeer. If we're reading up on this, don't confuse tire slip angle & car slip angle. Car slip angle is the direction the car is traveling, versus the direction of the wheels, as determined by the car's inertia at the time the tires lost some degree of traction.

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Ackerman usually needs to be designed in. In many production cars, with production spindles, increasing Ackerman can be challenging. In designing in Ackerman, steering arm & rack or tie rod placement is VERY critical. I'm going to explain everything at first with a rack & pinion, then clarify drag link steering at the end.

Fore and aft placement of the rack:
Of course, the dimensions of the UCA & LCA pivots ... along with rack width & height placement of the rack ... play the key roles in bump steer. Let's assume we're going to place the rack at the proper height to achieve minimal bump steer, with the Bump-Out being smooth. Then the keys to achieving the target Ackerman are moving the rack back closer to the FACL & utilizing spindles with proper offset steering arms.

Locating the rack back closer to FACL sounds easy on paper, but it is very challenging in the real world of metal tubing, engines & moving suspension parts. There are almost always conflicts. For example, in pro road race cars where a key goal is getting the CG low ... we want to mount the engine low. If rules prevent us from moving the engine very far back, the balancer or engine itself, are in the space we need the rack. Then we have a dilemma. Do I raise the engine & CG to gain Ackerman, or accept less Ackerman to achieve the lower CG?

Utilizing a spindle with offset steering arm can get some of that Ackerman back. Getting more Ackerman when designing a rear steer spindle is a walk in the park, because we're moving the outer tie rod
pivot in & away from the brake rotor. For front steer ... getting more Ackerman in the spindle is achieved by moving the outer tie rod outward & closer to the brake rotor. The brake rotor is typically the limiting factor. In wide spaced stock car spindles that create a lot of Scrub Radius it's not usually a challenge. But in correctly designed narrow road racing spindles that utilize low KPI angles & low Scrub Radius ... combined with wide brake rotors ... the rotor is the limiting factor. Basically, it is another packaging challenge.

For most of my RSRT front ends I designed tight spindle & hub packages that utilize a 1.25" wide rotor, 5° KPI, zero Scrub Radius & high Ackerman. It took a lot of work & testing to make it all fit & work well with proper clearances. These utilize a steering arm that is about .650" outward (depending on LBJ height) from the KPI.

RSRT Track-Pro Spindle: 5° KPI / 3.314" from WMS to KPI Axis
RSRT GrandAm Spindle: 5° KPI / 3.855" from WMS to KPI Axis
RSRT Track-Star Spindle: 5° KPI / 3.855" from WMS to KPI Axis
RSRT Race-Star Spindle: 5° KPI / 3.314" from WMS to KPI Axis
RSRT GT Spindle: 5° KPI / 3.855" from WMS to KPI Axis

That is plenty for our track & autocross packages, due to no engine location rules. But our Race-Warrior packages that fit into Trans Am & SCCA classes have strict engine location rules. These required a completely new spindle with an even lower WMS to KPI Axis & the steering arm offset outward even more. We built several steering arms, for tuning Ackerman, with the highest about .950" outward from the KPI axis, depending on the height of the LBJ.

RSRT Pro-GT Spindle: 5° KPI / 2.285" from WMS to KPI Axis / True KPI Axis

If we measure production or stock car spindles that number will be quite larger. If we're sticking with those spindles & high scrub radius, then at least run a steering arm with lots of offset to move the outer tie rod toward the rotor to increase our Ackerman. We can see how close I put the outer tie rod to the rotors if we look at the illustration below.

Now, with steering box cars that utilize a centerlink (aka drag link) the concept is the same. Everything about offset steering arms is the same. Just think of the inner tie rod locations as rack pivot locations. For years in oval track racing we ran aftermarket centerlinks. Some of these relocated the inner tie rods outward to help with bump steer incurred from our relocated control arm geometry. They all used slugs with a series of offset holes to relocate the inner tie rod up or down to achieve our bump steer goals.

Some Racers didn't realize they could tune Ackerman to a degree as well with these packages. Since we were using rod ends with spacers & bolts, instead of OEM style tapered tie rod ends, we could run longer bolts & spacers to move the inner tie rods towards the FACL. This increased Ackerman, if we need to. Many OEM frames have a section of frame in the way to getting aggressive with this. We simply cut that section off & capped it with steel plate. (See photos)

In Summary:
Achieving Ackerman is all about the angle of the tie rod to the steering arm. In addition to offset steering arms, Here's a quick guide:
A. Moving the rack (or inner tie rods) back towards the FACL ... increases the angle of the tie rod to the steering arm ... and increases Ackerman.
B. Moving the rack (or inner tie rods) forward away from the front axle centerline ... decreases the angle of the tie rod to the steering arm ... and decreases Ackerman.
C. Moving the outer tie rod back on the steering arm towards the front axle centerline ... via slots or changing the arm ... decreases the angle of the tie rod to the steering arm ... and decreases Ackerman.
D. Moving the outer tie rod forward on the steering arm away from the front axle centerline ... via slots or changing the arm ... increases the angle of the tie rod to the steering arm ... and increases Ackerman.

As far as Ackerman is concerned changing the angle of tie rods to the steering arm utilizing any of these 4 methods has the same effect. But A & B do not change the steering speed ... while C & D do change the steering speed.

Reminders:
1.    If we switch steering arms to more or less offset, we are changing the tie rod length & therefore our bump steer curve. If we do this to achieve the optimum Ackerman, we simply need to re-bump steer the vehicle.
2.    Anytime we can't get enough Ackerman in a competition vehicle, remember we may increase the Bump Out.
3.    If we need to reduce Ackerman, I suggest decreasing the amount of Bump Out first.

Toe-Out, ACKERMAN & Bump-Out:
Because I design & build race cars ... and this thread is about optimizing race/track cars ... I will clarify a few details. From my years of racing experience, I have found that running Static Toe-Out makes the tires (and therefore the car) more responsive upon initial steering input. So, I often run Static Toe-Out in the range of 1/16"-3/16" total. I also, often run "bump out" ... which is additional Toe-Out Gained, when
the front suspension compresses under braking (aka "dive"). This helps the inside front tire get to optimum slip angle sooner & turn in better when braking hard into tight corners.

As the steering is turned I have "some" Ackerman in the steering system to continue to add "dynamic toe out" to the inside tire as the steering is turned farther & farther. Exactly how much Static Toe-Out, how much "bump-out" & how much Ackerman I use to achieve the optimum "dynamic toe out" depends
on the:
* Mixture of turn radius, corner speed variation & g-force variations
* Roll angle of the car in those different turns
* Optimum tire slip angle, which varies with sizes & designs.

So, in full dive, rolled over & turned XX° ... I may target as much as 100% Ackerman in certain cases I'll explain later. But we usually find less than 100% Ackerman is optimum. It is all depending on what the inside front tire needs to achieve optimum slip angle. Because optimum slip angle is the only reason to turn the inside front tire more than the outside front tire ... when racing.

Tip: Most stock oem production cars call for toe-in from the factory. If we do the math & get in-depth in this, we may notice that Static toe out ... then additional Toe-Out through bump steer in dive ... makes the actual net Ackerman higher in the first 5-10-15 degrees of turning. So, if we tried to run 100% Ackerman ... plus Static toe out & bump out ... we would have too much. So, we run less Ackerman to work with the Static toe & bump out.

Some tracks reward more Ackerman and less Static toe out and/or bump out. Some tracks reward less Ackerman and more Static toe out and/or bump out. This mixture is something I turn for each track when competition is tough. The ultimate goal, is to get the optimum slip angle for the inside front tire ... in the corners ... which vary.

So, in conclusion, there is no set number that is optimum for all situations. I suggest, we run the Performance Trends Suspension Analyzer software with our car in full dive, full Roll Angle and see where the dynamic toe (Ackerman in the program) is for different steering angles. I find what works best
is more than what's recommended in the lower steering angles and close to what's recommended with higher steering angles.

The old fashioned way of figuring out how much Ackerman a car had involved plotting the car's steering arm angles back to the center point of the rear of the rear axle. They way Ackerman is calculated, is affected by the track width of the car, as well as the wheelbase, so every car is different. "Back in the day" we would use strings to simulate these steering arm angles on the shop floor & find the intersect point.

Sweet Steering has a good tech paper on this located HERE.

For example, purposes only, if we had a car with a 100" wheelbase ...
* If the steering lines intersected under the rear axle pumpkin right at the 100" rear axle centerline, this was considered 100% Ackerman. (It was not accurate, but more on that later.)
* If the steering lines intersected past the rear axle, 10" behind the rear axle centerline, this was considered 90% Ackerman. 20" behind would have been 80% Ackerman, and so on.
* If the steering lines intersected before the rear axle, 10" ahead of the rear axle centerline, this was considered 110% Ackerman. 20" ahead of would have been 120% Ackerman, and so on.

The old method is not accurate, as it does not take into account the tie rod angle to the steering arm, which is a major factor. For this reason, I haven't used string & plotted a car in decades. Today's software takes in all the factors to accurate tell us how much Ackerman we have. Suspension Analyzer 2.4 from Performance Trends will show us both the steering angle differences from side-to-side and what they call Ackerman error.

At a quick glance I can see the steering angle differences when I'm in the software. As I mentioned earlier, wheelbase & trackwidth play a role what constitutes 100% Ackerman, so cars vary. But I work with a lot of cars today that are similar to each other ... say 108" WB & 58" track width. So even though they vary from that, it's not a lot.

Due to many of my clients today autocrossing, I put steering into the software to get the outside tire turned 25.0° ... then I look at the inside tire steering angle. 100% Ackerman is typically around 6-7° more with these cars ... so my inside front tire should be turned 31-32° ... if I'm expecting 100% Ackerman. I do not expect this from production cars. They rarely have enough Ackerman, without modification. I'll show we how I do this ... which is just one way of several methods. To respond to our question,
I opened an actual file, so I'd have real numbers. I did round the numbers off to make the math easier, as well as the conversation.

In the software, I added steering until the outside tire was at 25.00°
* The inside tire was at 29.50°
* Some people would refer to this 4.5° difference as "4.50° of Ackerman @ 25° Steering angle."
* The software showed me 100% Ackerman would have had these 2 wheels at 24.25° & 30.75° ... which is a 6.50° difference.

To clarify ...
* A 6.50° difference would be 100% Ackerman
* This car had 4.5° difference

To figure the percentage of Ackerman this car had, we simply take 4.5 and dived it by
6.5. This equals 0.692. That is 69.2% of Ackerman. This is how I calculate it. The
software provides me with the 100% number & I compare what we really have in the car
to that.

As a rule of thumb, I have found ... the flatter we run our car, loading & working the inside front tire more, the less Ackerman % we need ... but we still need a certain amount. The more Roll Angle we run with our car, the less we are loading & working the inside front tire and the more Ackerman we need, up to the point it doesn't matter. If our suspension strategy has the car's body/chassis Roll Angle much MORE than 3° ... it almost doesn't matter what our Ackerman is, because we're not loading & working that inside tire when the car is turning.

There are variables we typically can't account for, such as:
* What is the optimum slip angle for the tires we run?
* Exactly how much are we loading the inside front tire?

In professional racing, we make the Ackerman "tunable" & test. Like in my Track-Warrior front frame & suspension packages, we make the rack mount slotted fore & aft, so it's tunable. *Readers, if we're not familiar with this, for front steer cars, moving the rack forward reduces Ackerman & moving it rearward increases Ackerman. (Same thing with the tie rods on a centerlink.) Rear steer is the reverse.

On our test days, we would start a little shy of where I thought we needed to be & add some Ackerman each run until we found optimum. The driver (and data acquisition, as well as the stopwatch) would tell us the car turned better ... each time ... until we went too far. Then the car would get a little tight. We'd back it up to the happy spot & lock it down. From there we would not tune on Ackerman on that car ... unless we had a change in tire brand/model/design.

7. Tires & Wheels
Captain Obvious here, tires are the only thing connecting the race car to the track. They are the #1, most important, highest priority to grip in a race car. Any race car. If you race in a series or class that has tire & wheel rules, other than following them, the only advice I have is always run FRESH tires.

I'm not referring to tread depth. Tire age is key. The rubber in tires begins curing the instant they are poured in a mold & never stop hardening. Running old tires on a race car to "save money" is the dumbest thing you'll ever say. It completely throws away the event. Test, play, fun track day or race, buy & run fresh tires. If you call or text me trying to sort out your hot rod on old tires, I will laugh & hang up on you. Yes. I. Will. No sense in both of us wasting our day.

Now, if you're building a track car, time attack car or race car with no tire rules, it behooves us to run the best tire we can. Best usually, but not always, means highest grip. If you run endurance racing, we need to consider wear & temperature management. Size matters. Typically, we want to run the biggest tires we can, but there are exceptions. If you're building a bodied race car that is light and or low powered, tire friction & rolling resistance comes into play.

For road race cars that run 4 cylinder race engines in the 200-300HP range, we run race slicks no wider than 315's. For 400-450HP we'll run 335's rear & 315's front. Yes, an exception to my all 4 tires the same size guideline. Beyond 500HP, & up to 700HP, we'll run 335s all around. Above 700HP I like to run even wider tires. I only run the 345/35-18s when we want the tire to fill up the fenderwell better, like on a stock car. They're taller than I like at 26.8" (with a taller sidewall) ... compared to 335/30-18's at 25.6" with over 1/2" shorter sidewalls.

I LOVE the Hoosier 355/650R18. It's 25.8" tall with 13.50" tread width compared to 12.8" for a 335. Plus the S2 compound is a little faster than the Hoosier "A". I love to run this tire on all 4 corners of race cars, up to about 850-900HP. After that, we see a lap time advantage running the 1" wider tread Hoosier 365/720R18 (14.50" tread). I don't like the 28.20" height of the 365/720R18 for lateral G's, but it does help with initial throttle roll on & corner exit grip with 900HP + race engines.

Rookie Racers often don't know how critical tire width to rim width ratio is to grip. We often see people putting good width tires on narrower than ideal wheels ... usually to suck the sidewalls in for fender clearance ... and experience significantly less grip. An example is when Racers want to put a 315 tire with 11.8" of tread on a 10.5" wheel. Not good.

The optimum wheel width for grip varies with sidewall height & design. Stock Car bias ply tires have 6"-7" sidewalls & respond well to wheels around 10% wider than tread width. Modern cars with 18" wheels & 30 or 35 series radial tires have 3.5"-4" sidewalls & respond well to wheels equal to tread width or 2-3% wider than tread width.

If the rim to tire ratio is narrow, the sidewalls are bulging out past the rim, and we run less tire pressure to achieve even tread wear. This is bad. The lower pressure is not enough to keep the tire carcass in the proper shape with high G side loads (even worse with taller sidewalls). So, the tires "roll under" significantly during cornering. This distorts the tread contact pattern.

This is WHY we have less grip with narrow wheels. Wider wheels require more tire pressure to achieve even tread wear & this keeps the tire carcass in the proper shape with less roll under. A bonus advantage to wider wheels & higher pressures is, the optimum slip angle is lowered. This makes the tire respond quicker to driver input.

For 18" wheels with radials, treaded or slicks, we recommend:
For 315/30-18 tires with 11.8" of Tread, we recommend 11" min, 11.5" is better, 12" is best.
For 335/35-18 tires with 12.7" of Tread, we recommend 12" min, 12.5" is better, 13" is best.
For 345/35-18 tires with 13.2" of Tread, we recommend 12.5" min, 13" is better, 13.5" is best.

Unfortunately, many series rules limit rim size, as they know running wider rims is an advantage. SCCA GT1 limits the 355/650R/18 fronts to 13" & the 365/720R18 rears to 14". They would both benefit grip-wise with ½"to 1" wider rims if you're not racing under SCCA rules.

Trans Am limits the Pirelli 320/660-18 to 13" wheel, which is awesome for the 11.85" tread width. Similar with the 350/720-18. It is limited to a 14" rim & has 13.10" tread width. Great rim to tread width ratio.

8. Unsprung Weight
I always believed I wanted the lightest wheels to reduce unsprung weight. I was wrong. The goal in running lighter wheels (and other things) was to get the suspension to follow the track undulations the best. The proven, real world objective is to keep the tire loaded over track undulations. This is why 6, 7 & 8-post machines exist. They help pro level race teams figure this out BEFORE going to the track. Later on, I learned wheel rigidity is just as, if not more important than weight.

Believe it or not, I learned this next bit of wisdom kart racing. I was running the lightest spun aluminum wheels (Van-K for you old Kart Guys) and never thought otherwise. A good friend of mine, race car builder extraordinaire Ray Cunningham, suggested some cast magnesium wheels that were heavier but more rigid. Holy crap they had more grip. Better front grip & turn in. Better rear grip. Faster lap times. Yet they were heavier.

I learned in road racing full bodied, tube chassis race cars, with aero, that ultra-light wheels flex too much & allow the tire carcass to distort. Not good for the footprint, contact patch or grip. As we put the same tires on stronger (but heavier) wheels we went faster. So, I was on an eternal search for the lightest, strong wheels. Until I ran Forgeline wheels. They have 5 wheel designs that are perfect. They are the best balance of strength, rigidity & lightness.

The factory Porsche teams runs Forgelines & asked them one time to take 3/4 of a pound out of each wheel. Forgeline's engineers told them that's not the way to go. But us racers gotta try stuff ourselves sometimes. Porsche put the lighter wheels on & went slower ... thinking it was some other handling problem. Forgeline suggested they put the regular wheels back on ... and viola ... the handling problems went away & they went quicker. I'm no shill for them. I simply love a well-engineered product I can count on. We run nothing else.

Nonetheless, we want the lightest, strong wheels we can & ideally, we want the rest of the unsprung weight to be light as is practical. By practical, I mean it has to survive a certain amount of usage before failing. If you make something so strong it would never fail, after extended racing use, you overbuilt that part. I'm not saying we want these things to break. I'm saying don't over burden them with excess weight.

The components that are "unsprung" ... meaning they are not held up by the springs include:
•    Tire & Wheel
•    Lug Nuts
•    Hubs
•    Spindle/Upright
•    Ball Joints
•    Brake Caliper & Mounts
•    Brake Rotor & Hat
•    Half the UCA
•    Half the LCA & Strut Rod
•    Half the Tie Rod
•    Half the Sway Bar Arm
•    Half the Shock & Spring



Let's also recognize we shouldn't choose our brakes by weight only. The lightest brakes probably won't produce the best lap times or last very many laps without overheating. Same with sway bar arms. I won't run aluminum sway bar arms in the front, where we have really high rates. Why? because aluminum is not as responsive as steel arms. And ... if the rate is really high, we'll see some flex. Aluminum arms in front would reduce rate & responsiveness.  There are ways to get lighter steel front sway bar arms. They need to be hollow, typically TIG welded chromoly sheet, formed in the shape needed. Lighter, but pretty expensive. We offer these as an option on Race-Warriors.

9. Front Tire Contact Patch
Achieving the optimum (fullest) contact patch of both front tires, dynamically in full dive, roll, steering & braking in the corner, is a critical key to grip. No good having 12" wide tread if we're loading it all & getting the most grip possible. This is not easy, with a lot of factors affecting the final contact patch. Wheel load, tire roll, chassis roll, camber setting & gain, caster setting & gain, spindle KPI, steering angle, etc., all affect the final contact patch. The combination of all these factors, minus wheel load & tire roll, is called dynamic camber.

Over four decades I have learned the dynamic camber needed to achieve optimum contact patches on both front tires on vehicles with a range of weights, varied tire designs, different sidewall heights & wheel-width-to-tire-width ratios. There is a lot more information on this in the forum section on Front Suspension & Steering Geometry.

Some basic things to know are:
•    Camber helps the outside tire & hurts the inside tire
•    KPI helps the inside tire & hurts the outside tire
•    Caster helps both the inside & outside tire

When are 5° or 8° KPI spindles better? It has to do with the travel & roll angle of the suspension strategy. When Ron works out a suspension & steering geometry setup, he utilizes a 3D suspension software that allows him to look at the tire contact patches when the car is in dynamic dive & roll. Like the illustration to the right.

Then I work with both static & dynamic camber & caster, as well as the spindle KPI to achieve optimum contact patches for both front tires. Utilizing 5° spindles helps Ultra High Travel/Low-Roll setups achieve optimum tire contact patch. The 8° spindles work better with Moderate Travel/Moderate-Roll setups to achieve optimum tire contact patch.


 
10. Rear Tire Contact Patch
First, so everyone is on the same page, Racers & Manufacturers use the term "Cambered" in this instance of rear end housing ends ... regardless if we end up with a camber change or a toe change on the rear tires. In my comments, I will use the appropriate term, so it's clear in everyone's minds.

Second, which way you mount the "cambered hubs" to angle the tires ...of the four common options ... in at top for negative camber ... in at front for toe-in ... or in at back for toe-out ... or some combination of camber & toe ... is dependent on your tuning goals.

Third, how much ... as in how many degrees do you do any of these ... can be dependent on tire slip angle & chassis roll angle.

Let's discuss what each does ... why you would care ... and go from there.

1. Negative camber of the rear tires ... in small amounts ... would help the outside rear tire run with a flatter contact patch, giving it more grip. Just as in the front end, camber helps the contact patch of the outside tire & hurts the contact patch of the inside tire, by tipping it the wrong direction. But the loss is not a "1-for-1" kind of thing.

The outside rear tire is loaded more, so it "rolls under" more than the inside rear tire. If you add just enough negative camber to the rear tires to optimize the outside rear tire's contact patch ... you won't hurt the contact patch & grip of the inside rear tire very much. The gain in grip on the outside rear tire will exceed the loss of grip on the inside rear tire, netting an overall grip increase.  Besides ... you need to disengage the inside rear tire to a degree anyway, to get the car to turn.

This makes sense, providing you feel you need more rear tire grip. In my experience, with adjustable rear suspensions, I've never been in a situation where I couldn't get all the rear grip we needed. So, the question is not will it help rear grip ... it will. The question is do we need more rear grip?

In my experience, the times this would make sense are when we have a road course Track Car, AutoX or Race Car with MORE weight bias in rear than front. Like Formula Fords & ... hmmmm. Only a few PT cars achieve a higher rear weight bias.

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2. Toe-in of the rear tires ... takes the outside rear tire (in whatever corner) & turns it "inward" to add slip angle. This makes the outside rear tire have grip sooner & respond quicker on corner entry. This is quite common in road racing, as it builds confidence in the driver. But there are many negative side effects. In my opinion, the side effects are not worth it.

Side effects:
a. The outside rear tire gets to the optimum slip angle at a lower corner speed, reducing that tire's ultimate corner speed capability.
b. The toe-in of the two rear tires ... say 1° each for a total of 2° toe-in ... creates unwanted scrubbing of the rear tires. This builds heat, misleading the crew into thinking they're working the rear tires better.
c. The poor inside rear tire is turned the opposite direction for optimum slip angle, and therefore has less grip throughout every section of the corner.
d. Toe-in of the rear tires reduces the rear steer effect of slip angle. That rear steer effect is needed to offset the counter steer effect the slip angle produces in the front end. So, we end up with a tighter race car ... prone to pushing & understeer.

I feel rear toe-in is a band-aid for old design, tall sidewall tires and/or cars with a rear heavy weight bias that need additional grip on corner entry

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3. Toe-out of the rear tires ... takes the outside rear tire (in whatever corner) & turns it "outward" to reduce slip angle. This makes the outside rear tire have grip later & respond later ... so the car may feel loose on entry. But the outside rear tire gets to the optimum slip angle at a higher corner speed, increasing that tire's ultimate corner speed capability.

The inside rear tire is turned the correct direction for optimum slip angle, and therefore has more grip throughout every section of the corner. Now both tires have more grip & the capability for the back end of the car to carry more corner speed ... if the front is also capable. But the biggest effect toe-out of the rear tires produces ... is increased rear steer effect of slip angle. This increased rear steer effect makes the car turn better ... to help offset the counter steer effect the slip angle produces in the front end. 

There are concerns:
a. The toe-out of the two rear tires ... say 1° each for a total of 2° toe-out ... creates unwanted scrubbing of the rear tires. This builds heat, misleading the crew into thinking they're working the rear tires better. It builds heat on the inner edges of the rear tires, clouding the picture of whether the team is properly working the contact patch correctly in the corners.
b. The car does feel looser on initial corner turn in.
c. The extra rear tire grip balances out the rear steer effect ... otherwise the additional rear tire grip is not needed, nor a benefit.
d. It is debatable whether the increased rear steer effect is needed, unless the parameters of the car make it hard to optimize the front suspension & geometry.
Where it may make sense, is long wheelbase, front heavy PT & Track cars ... as long as the driver can get comfortable with the loose feeling on initial corner turn in.

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Opinion:
I have a lot of tricks I use in building winning cars. For oval track, especially with the funky weight bias & scrub radius we end up with ... rear tire camber & toe out make a lot of sense. For hardcore PT car, track cars or race cars running road courses and/or AutoX ... I don't see the gain amounting to much, unless you're tracking a real front heavy and/or long wheelbase car. My personal hardcore PT car will be close to 50/50 weight balance, so I don't plan to run any camber or toe in the rear end.
Summary:

There are advantages, side effects & concerns ... just like most things. If you have a real need to utilize one of these tuning tools, hopefully you now understand them a bit better & can proceed.

Test: 
If you're not sure ... are intrigued ... and have the resources ... set up your rear end with switchable hub plates ... buy a set of square mounts & 1-2 different angle mounts and go track test. In this case, I would start with a set of 1.5° hubs & rotate them to provide 1° of negative camber & .5° of toe-out ... and compare that to the square mounts. Of course, I think this test should come after you have worked out the car many, many days on track & have it pretty dialed in.

11. Spring Rate vs Spring Load
Spring rate vs spring load can be confusing. Spring rate is typically thought of as the number of pounds to compress a spring 1". Unfortunately springs are not perfectly linear, so the rate varies a little over different spring compression amounts. By this I mean the first inch of compression might be 385#, the second inch 405#, the third inch 398#, the fourth inch 401# & so on.

This is a 400# spring. Just realize they're not perfect. Draco & Renton springs are the closest to perfect you can buy, because they dyno every spring & throw out the ones that don't met their standards. You even get the spring dyno sheet, so you see how close to linear your spring is, and where it varies.

Spring load aka spring force is the stored energy, rated in total pounds of force, of a compressed spring. Let's use the same spring as above in an example. If we put this spring on the right front (just an example) and the corner weight of the race car compressed this spring two inches exactly, we know the spring load is 790#. Sitting there ... statically ... at ride height.

Now, when we drive off hard into turn 6 at Webefast Speedway, and the front end dives enough to compress this same spring another two inches exactly, we know (from the numbers above) the spring load is 1589#. This is 799# MORE force pushing down on the spring & suspension (and by association the tire) loading it signficantly more for increased grip. It's not a one-to-one. We need to take the control arm motio ratio into account to get wheel rate.

12. Spring Rate vs Wheel Rate
Here is the Coil-Over formula:
B/C = D² x Cos = MR
B = The dimension from CL of LCA pivot to CL of lower shock mount.
C = The dimension from CL of LCA pivot to center of the ball joint.
B/C = D
Now, we square it for spring rate calculation = D²
*This is because there are two control arms.

Then we factor in the Cosine angle (geometry speak for angle calculation)
Cos = The Cosine factor based on shock angle (I use a chart or spread sheet formula)

For example:
B = 16"
C = 20"
B/C = D = .80 > D² = .64
Cos = For a 22° shock angle is .927
D² = .64 x Cos factor of .927 = .5933 > This is our Final "net" Motion Ratio to figure out Wheel Rates.



13. Tire Loading for Grip
There are a handful of things that "load" the tires.
1.    The weight of the car in general. The corner weights of the car specifically.
2.    Load transfer from braking, turning and/or accelerating.
3.    Spring rates
4.    Spring load/force
5.    Aerodynamics

Front Tire Loading:
We can determine the static spring rate, at rest & ride height on the scales. This corner is using 790# of spring rate to hold it up. 790# x .5933 = 468.7# spring force to hold the car up, with that particular cross weight & corner weights. If we adjust the cross & corner weights, this will change as well. Now this number takes into account the corner weight minus unsprung weight. Said another way, this 468.7# is NOT the corner weight. It is the corner weight MINUS the unsprung weight.

The corner weight might be 600#, higher or lower, depending upon cross weight adjustments. For conversation's sake, let's say it is 600#. Statically, that is how much tire loading we have ... 600#. Until we drive off hard into turn 6 at Webefast Speedway, and the front end dives enough to compress this same spring another two inches exactly. Which we know to be 799# of spring force. To determine the wheel force, we take the 799# x .5933 mr = 474#.

What does that mean? It means, in that instant, we dynamically now have 474# + 600# = 1074# of wheel loading. What about aero? Well, if the car has aero, that is with aero. How do we know? Because it compressed the spring exactly 2" ... and the math shows us that adds 474# of force loading the tire.

If that number was without any aero on the car ... and we added effective aero to the front of the race car, the spring would compress more. How much more, depends on how effective the aero really is. The spring rate & spring compression allow us to calculate how much wheel load we have. Make sense?

By the way, the wheel rate from this example would have been 400# x .5933 = 237.3#. But that's not what the conversation was about. So, don't confuse the wheel rate with wheel/tire loading..

Opposite end & opposite corner:
Just remember, what you do with spring & bar rates affect the grip on the other end of the car, specifically the opposite corner more. You'll learn this is detail in the Track Tuning for Handling Balance forum on this site.

Rear Tire Loading:
It may seem odd, but we don't chase the loaded spring force & wheel force numbers in the rear. I'm not saying the wheel rates & wheel loads don't matter. They do. But they don't guide us as much as the front, because the rear of the car is not traveling like the front under braking.

Where rear spring rates, spring loading, wheel rates & wheel loading matter primarily is in the roll through zone. This is when you're off brake & off throttle. Some call it coasting. We call it the "roll through zone" because we're letting the car keep more of its corner speed by "letting it roll" than by continuous trail braking which slows the car's corner speed.

The software I utilize, Performance Trends Suspension Analyzer, utilizes the spring rates, bar rates, motion ratios & total wheel loading along with track width, CG & roll centers to determine the cars roll angle per 1 g-force & the handling balance number called Front Lateral Load Distribution. I use that FLLD number to know the car's balance, or lack of, & tune from there.

Let me repeat this & we'll move on. As far as the rear is concerned, we only care about rear spring rates, bar rates, loading, wheel rates & wheel loading ... in the roll through zone. Off throttle & off brake. At these times, the linkage of the rear suspension is not doing much, other than holding the rear axle in place. Literally. Anti-squat (and pro-squat if you have a decoupled suspension) are meaningless in the roll through zone. Why? There is no torque present for the link suspension to act as a lever on.

As soon as we apply power or brake, we are introducing torque to the rear end & the linkage NOW plays a role in the handling of the race car. Getting the car to hook up and accelerate out of the corner is an easier goal to achieve than getting the front to work & the car to turn well in the middle of the corner when driven at its limits on tight corners.

So, assuming we have dialed the front suspension in to turn well in the middle ... and now we're working on maximum forward bite (rear tire grip) on corner exit ... here are the suspension areas to focus on ... to create more rear mechanical grip.

Areas of Focus:
• Anti-squat
• Length of Swing Arm Instant Center
• Rear shock valving
• Torque Distribution
• Torque Absorption
• Rear Steer

The amount of leverage ... anti-squat % ... you tune into the rear suspension is a key factor. More anti-squat, more grip on exit. The compromise is more anti-squat frees up the rear tire grip on corner entry (Unless you're running a decoupled rear suspension). Rear aero downforce, with an effective spoiler or wing, is a good tool to add rear grip to help your corner entry. With enough rear aero downforce, you can run higher anti-squat ... to have more exit grip ... with less concern of getting loose on entry.

Rule of thumb:
• Conventional set-ups can run around 50% AS ... and drive in deep without getting
loose on entry
• High Travel set-ups can run around 40% AS ... and drive in deep without getting
loose on entry
• Add 10%-30% to these numbers with aero downforce
• We can increase these numbers substantially with Decoupled 3-Link & Torque Arm rear suspensions.

The next major key is the length of the swing arm. In other words, how far forward you place the I/C. The shorter this is, the more instant the grip is ... but it fades as you drive out of the corner. The longer it is, the grip comes on slower but lasts longer. To put this in perspective, when I see the length of Swing Arm Instant Center around 30"-40" on a 105"-110" wheelbase car ... that is short. For this wheelbase of car, I consider 50"-60" moderate ... and 60"-80" as long.

Said simpler:
• The softer & longer you want to load the rear tires on exit ... the longer the swing arm needs to be.
• The harder and shorter you want to load the tires on exit ... the shorter the swing arm needs to be.
• I have had good racing success with long swing arm lengths ... with no "tricks".
• I have had better racing success with moderate swing arm lengths ... with some
"tricks" to keep the car from getting loose on corner entry.

Rear shock valving, if done right, can add grip to the rear tires on corner entry & corner exit. We do this with what is called "Tie Down" technology. It is achieved by modifying the bleed circuit, not the shim stack in the pistons. To not duplicate information, this is covered fully in the shock & valving section.

Torque distribution in the rear has to do with the length of the levers ... I mean brackets ... on the rear axle. OK, the brackets for your 3-Link, 4-Link, Torque Arm etc., act as levers. The length of the upper & lower brackets, relative to each other, define how torque from the powerplant is used to load the rear tires for grip & to move the car forward. Let's use a 3-Link as our example.

As torque comes to the rear axle, through the driveshaft, the rear end housing wants to rotate the pinion up. (Equal & opposite reaction to the axles roating the tires). The upper bracket & link is primarily LIFTING the car's mass to load the tires. The lower brackets are primary pushing the lower links & the car forward. Moving it forward.

If the upper & lower brackets are the same length, we have 50/50 torque distribution. But if the brackets are different lengths, we will have different levels of torque lifting & load tires versus pushing the car. When you build the rear end with the suspension brackets, you get to define how much of the engine power is lifting & loading the tires for grip. This is covered much more in-depth in the Rear Suspension & Geometry section of the forum.

I helped a big name autocross racer with a twin turbo LS get the rear grip he needed with this strategy. His lower link brackets were 5". His 4-Link uppers were 2". I had him convert the car to a 3-link with a torque absorber & install the top link bracket ... are you ready ... 13.5" above rear axle centerline. Not kidding. There was no sheetmetal in this area of the trunk to interfere. He literally rocketed out of the corners with no tire spin. It was so effective he said he thought the front wheels were pulling off the ground. They weren't, but it was close.

Remember grip can be violent. In drag racing, for the 1000-3000HP doorslammers, they go the other way. They shorten the top brackets in their 4-links to "tame" the launch & eliminate tire shake. In road racing we don't run 3000HP engines, thank goodness. Nor are our tires soft sidewalls with 4.5 PSI tire pressure. So tire shake is less of a concern, but not a zero concern, if you have power up in the 1000HP range

Torque absorption units can be used on 3-Links & Torque Arms. The purpose they achieve is to dampen the initial impact of the driver opening the throttle too quick & shocking the rear tires. Once you shock the tires, especially short sidewall tires on 18" wheels, the tires spin & it's hard to get them to stop. Once they overheat, the rear tires will have less grip, be loose & spin easily out of all the corners. Not good.

Yes, the driver needs to learn how to crack the throttle lightly & roll the throttle on nice & smooth. But all drivers can benefit from running torque absorbers in the rear. The improved initial rear grip allows the driver to be a more aggressive & get to full throttle quicker, without tire spin. Obviously this produces quicker lap times.

Rear Steer, also called roll steer, is when the rear tires point toward the outside or inside of the corner, when the chassis/body rolls. In Independent Rear Suspensions, this is achieved (or stopped) with toe-link geometry. With straight axles & linkage suspensions, the lower links are the tool create roll steer. If the links run uphill (going forward from the RACL) this will create positive roll steer. That means during chassis/body roll, the linkage will actually articulate the rear end (top view).

The link on the inside of the corner will pull the inside rear tire forward. The link on the outside of the corner will push the inside rear tire rearward. And like a forklift, we now have both rear tires steering towards the outside of the corner. This makes the race car turn easier, BUT it reduces rear tire grip, in doing so. Counter rear steer is the opposite. If the links run downhill (going forward from the RACL) the link on the inside of the corner will push the inside rear tire rearward & the link on the outside will pull the inside rear tire forward.

Now both rear tires of the race car are steering towards the inside of the corner. This increases rear tire grip in the corner, but makes the race car tighter & may be harder to turn. I look at rear steer as a band aid. I rarely use it. I have on race cars that didn't handle well, to band aid for a race event. But I improved the car after that event & always go back to zero roll rear steer, aka neutral roll steer. I do add counter rear steer in some IRS packages if the driver is a rookie & needs a little extra rear grip on entry to be safe. Frankly, for my front ends that turn so well, I don't find a need for positive rear steer.

14. Sway Bar Rate vs Sway Bar Load
Sway Bar rate vs Bar load is a little more confusing than spring rate versus spring load. Why? The springs are always loaded when the race car is on the ground. The sway bars are only loaded when the body rolls in the corner. Even then, it's dynamic. The rates of BOTH front & rear sway bars are progressive into the corner entry ... reaching max rate mid-corner ... and digressive coming out of the corner.

See the chart below. It is a right hand U-turn. Notice where the purple dotted lines are. They are indicitive of where the rates are progressing on corner entry, as the driver turns the car more gradually. And indicitive of where the rates are digressing on corner exit, as the driver unwinds the steering gradually.

There are 10 purple, dotted lines on each. You can think of them as 10% rate, then 20% rate, 30%, 40%, etc. all the way up to 100% of the rate when the steering is max & set. The area with no dotted lines is where the steering is max & "set" (not steering more or less). The colors of the driving line show brake (red), coast (blue) & throttle (green).



An absolute key to understanding what the race car is doing, is realizing the sway bars are ADDING rate to the outside wheel spring rate to achieve a higher total wheel rate, than the spring alone. But, only when cornering. This is one reason why soft spring & big bar combinations work so well. If the bar rate was always there, like springs, it would be too much wheel rate. This applies to the front & rear sway bars. Although it's reversed in the rear, where the springs are higher rate & the sway bar is a softer rate.

We need to look at the front sway bar, especially if we have a high rate bar, as adding significant wheel rate to the spring wheel rate. The formula to find out how much wheel rate a sway bar is adding is very similar to spring rate, except no Cosine factor for coil-over shock angle. We're using similar math & a similar example to the spring rate versus wheel rate section earlier. For this example, we're moving the front sway bar mount inward 2" from the coil-over mount, on the LCAs.

Here is the Sway Bar formula:
S/C = D² = MR
S = The dimension from CL of LCA pivot to CL of sway bar link mount (Blue Line Below).
C = The dimension from CL of LCA pivot to center of the ball joint.
S/C = D



Now, we square D for spring rate calculation = D² = MR. This is because there are two control arms. We do not need to actor in a cosine angle, as with an angled shock. The sway bar pulls straight on the LCA. Let's do the math now.

Our example:
S = 14"
C = 20"
S/C = D = .7 > D² = .49
.49 is our Final "net" Motion Ratio to figure out Wheel Rates for this front sway bar example. Now let's figure out the wheel rate statically & wheel force dynamically.

If the sway bar rate is 1550#, we do the math 1550# x .49 mr = 759.5# wheel rate per inch of sway bar arm travel. For this example, we need to know how wide the sway bar links are to determine sway bar twist & arm movement. I'm going to use our GTS Race-Warrior specs for this conversation, where the sway bar links are 47.00".

This is a smidge off topic, but years ago I figured out a 1" difference at 57.3" inches is 1°. I use this for a lot of things. Here we're going to use it to determine the sway bar math. 47" ÷ 57.3" = .82 or 82%

If our sway bar rate is 759.5# per inch & we're twisting the bar enough to move the arms .82" apart, we have 622.8# sway bar force (or loading). To know our wheel loading, we multiply that times our .49 motion ratio. 622.8# x .49mr = 305.2# wheel load.

This is 305.2# ADDITIONAL wheel loading, over the 1074# of wheel loading from the spring. So we are seeing a total of 1379.2# of total wheel load out at the right front tire, in this hypothetical example. Why or how does this matter to us? As a single number, it does not. Frankly, one number can be more confusing than helpful. It is helpful when we start to compare wheel load numbers. As you improve the car's grip, these numbers will show you why. When you add downforce & the springs travel farther, the math allows us to see how much real world downforce we gained.

Moving on to one last piece of understanding how sway bar works. The front sway bar in our example. The 1550# bar with 759.5# wheel rate ... that only moves .82" to exert 622.8# sway bar force. Which with our .49 motion ratio adds 305.2# of wheel load (or force). BUT ... it does not do it all at once upon corner turn in. The active wheel load/force goes from 0 to 305# ... progressively ... as the driver turns into the corner ... increasing all the way until the driver has the steering at the maximum. Drivers typical hold the wheel as steady as possible for a section of the turn. We call the steer "Set" when the driver is not adding turn in or unwinding.



The progression is not perfectly linear, nor constant, but it's close enough to discuss it this way. There are 10 purple dotted lines (in the image above) breaking down the steering turn in section ... until the steering gets to 100% (maximum steering effort). Think of the sway bar force increasing gradually like this at each of the 10 dotted lines ...

1.    30.5#
2.    61#
3.    91.5#
4.    122#
5.    152.5#
6.    183#
7.    213.5#
8.    244#
9.    274.5#
10.    305#

Then it stays 305# all the while the steering stays max or set. Now look at the image above again & find where it says Initial Unwind. That is the point in the corner where the Driver will START to unwind the steering. In this example, it is also not perfectly linear, nor constant, but it's close enough to discuss it this way.

There are 10 purple dotted lines (in the same image above) breaking down the steering unwind section ... until the steering gets to 100% unwound (straight). Think of the sway bar force reducing gradually like this at each of the 10 dotted lines ...

1.    274.5#
2.    244#
3.    213.5#
4.    183#
5.    152.5#
6.    122#
7.    91.5#
8.    61#
9.    30.5#
10.      0#

Once the car is back to 100% straight, the sway bar is effectively "0". Why or how does this matter to us? As a single set of numbers, it does not. But over time of your racing, as you run different setups, you can see how running less spring rate & more bar rate will perform, as well as if you run more spring rate & less bar rate.

The same monster front sway bar that helped keep the front end flatter (lower roll angle) when the jacking effect and diagonal g-forces were in place ... add grip back to the inside rear tire as you unwind the steering and flatten the car out.

Moving onto the rear sway bar. It works in the same way. Rear sway bars are progressive on corner entry ... from zero rate when the car is straight ... and progressive in rate as the car starts turns in ... reaching max rate near mid-corner when the steering gets to 100%. The rear bar is also digressive on corner exit from max rate back to zero rate as the steering unwinds gradually. Just remember the rear sway bar rate is adding to the outside rear spring, while it is lifting on the inside rear spring.

I love to fine tune the rear sway bar for mid corner grip & balance. The sway bars are one of the few tuning items that affect the mid-corner "roll through zone." Need the car to turn better here? Increase the
rear sway bar rate. Need more grip in the roll through zone?  Decrease the rear sway bar rate.

I designed our rear sway bar arms with 4 holes, .75" apart instead of 3 holes 1" apart for better
fine tuning. Plus, you can split holes, providing the RSRT rear sway bar with 7 rates! For example, if the bar specs out with 4 rates of 161#, 183#, 210# & 244# ... by splitting the links, you add 172#, 197# & 227# to your tuning tool box. This allows you to really fine tune the "Roll Through Zone" rear grip for near perfect neutral, balanced handling.

Switching gears again, if you have read much of my stuff, you know I rely on TRS, FLLD & RLLD numbers for roll angle & handling balance. Front Lateral Load Distribution is the total resistance to front roll, stated in pounds. Of course it takes into account the spring & bar rates. But the FLLD formula includes everything that matters from track width, CG, front end weight, roll center & more. The RLLD is the same but for the rear. It is always significantly less.

TRS is Total Roll Stiffness. It is the total of FLLD & RLLD combined. It gives us the whole car roll angle per 1g. And if from experience we know what kind of g-force this car will pull, we can determine this car's actual roll angle, dynamically on track. I also use the FLLD % of the TRS to determine balance. More on this in other areas of the forum threads.

In the image below is a different race car that discussed above. This illustrates the front & rear roll resistance, taking into account the sway bar is progressive ... maxed ... and then digressive. The numbers you see are the TRS (3970#), FLLD (2820#) & RLLD (1150#), not just the sway bar load/forces. The math breaks down the dynamic FLLD & RLLD at 10 points represented by the purple, dotted lines. From this, we understand the race car handling is not linear.

15. High Travel & Low Roll
Before I get to the revelation about energy dissipation & grip loss through springs, I need to establish some fundamental knowledge for everyone reading along. I don't know the race team, crew chief and/or engineer(s) that initiated the move to what we now call the modern suspension setup that embraces much higher front suspension travel and lower roll angles. So, I can't pinpoint exactly how old the strategy is for certain, but I know it is at least 35 years old, because it was common by the end of the 1980's in professional racing.

That may seem like a long time, and therefore this suspension strategy should be well established. It is & it isn't. There are no top teams in professional racing of full bodied cars not running the modern high travel/low roll strategy. If a team showed up with an old school conventional low travel/high roll set-up in GT, ALMS, Grand Am, NASCAR Cup, Nationwide, Trucks or ARCA ... they wouldn't be fast enough to qualify for the field ... let alone be competitive in the race.

But at the grass roots racing level, the high front suspension travel and low roll angle strategy is still relatively "new."

I entered a series in 2010 that was new to me ... NASCAR Modifieds on the West Coast. There was an awesome veteran team that dominated the series for several years with a very well developed conventional low travel/high roll set-up. Most of the racers looked at that team as unbeatable unless they broke.

In 2010, they got beat 5 times. Once by another veteran racer that employed a crew chief with a modern setup & coil bind. And four times by my 2 cars with a modern set-up on bump stops ... and wet-behind-the-ears teenage "rookie drivers in development" I might add. The next year in 2011, the track changed the rules & outlawed bump stops. We adapted and ran coil bind set-ups some races ... and non-coil bind, soft spring/big bar set-ups other races ... and won 4 times again, with different rookie drivers.

Now in 2013, all the top teams in that series run a high travel/low roll set-up, some on coil bind, some on bump stops & some not. This includes the veteran team that was dominating before. They don't dominate like they once did, but they still win a lot, because they are a good team with good equipment & a great driver. They could have stayed with the old school set-up ... struggled ... and cursed this new technology. Or they could learn, adapt & advance with the technology ... which is what they did. It is a choice I see a lot of racers struggling with in all forms of grass roots racing across the nation. Stay with what we know? ... or learn this new stuff and advance once we figure it out.

And "figuring it out" is necessary for a veteran racer, because almost every item in the set-up is different. Racers that just simply put soft springs (with or without bump stops) in the front ... run worse. The spring rates to make it work are different front & rear. Heck they seem backwards. If a guy was running 600's in the front & 275's in the rear ... now he's running 300's in the front & 600's in the rear. The shock valving is very different. Even how the curves & bleed valves work are different. The roll centers needed are different. Obviously the sway bars are different. The more you embrace the strategy the bigger the sway bars get. In top levels of racing the sway bar rates are mind boggling. The optimum front geometry is different, because the car rolls less. It is different.


Here are some of the key advantages of a modern, high travel/low roll set-up ...
• Substantially more weight bias shifted to the front tires on corner entry & middle for increased front tire grip.
• Substantially lower CG in the front, when it matters, during cornering.
• Twice the travel ... which we learned travel by itself helps the car transition from accelerating to braking & cornering then back to accelerating.
• More compression travel on corner entry ... means more extension travel and rear tire grip on corner exit. Best of both worlds.
• Flatter roll angle works the inside tires substantially more. It's no stretch to understand four tires are faster than two.
• Significantly lower front end, during dive, lets less airflow under the car, providing way more front end downforce for increased cornering grip.
• The rake of the car in a corner, with the rear at or near ride height, allows airflow under the car to exit quicker, decreasing lift & increasing grip.
• I get a kick out of armchair tuners that think the key advantage is only aerodynamic, but aerodynamics are a nice advantage. At super high speed tracks, this advantage is obviously huge. On road courses, it is still very significant, but on tight AutoX tracks, it is a non-factor.

As I've said before, a well-developed & highly refined conventional set-up is fast. Just installing a modern set-up doesn't mean a new team & driver can come in & beat the veteran team(s) running conventional set-ups ... until the new team also gets their set-up well developed & highly refined. Then they will have a handling advantage. That alone doesn't mean they will win races. It still takes power, driving, strategy, etc. But the modern suspension set-up, when dialed in, is an advantage. There is no question or discussion amongst knowledgeable, professional tuners, engineers & crew chiefs. It is fact.

Now, along the way in the 25+ year journey of tuning, developing & refining this modern high travel/low roll set-up, a lot of things were learned. Of course, it will never stop evolving. We'll never stop learning & improving. And no one ever has it perfect on any given day ... just better than the rest of the racers ... providing the opportunity to win.

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16. Modern Spring Materials
A spring is a spring. Not!
Spring technology is a lot more complicated than most people know. Materials, designs & a myriad of processes create springs with different dynamic characteristics ... way beyond simple "pounds-per-inch" ratings. Every day spring technology is evolving as spring designers develop new & better ways to handle dynamic stresses, harmonics, energy dissipation, cycles & forces to prevent fatigue.
Spring rate ... as in "pounds-per-inch" ... show up on a spring rate tester. What doesn't show up is spring energy & responsiveness.
Brand new poor quality springs, made of cheap spring steel, can be made to achieve any "pounds-per-inch" rate we want in a spring. But they will not be as responsive as springs made with better spring steel.

The 4000, 5000 or 9000 series grades of spring steel are of higher quality than the typical 2000 series spring steel OEMs use. A simple rule of thumb is the higher the number, the higher the quality. Even though the 4000 series material is much better than common automotive spring steel, I do not run springs made from 4000 series steel. I have run springs made with 5000 series steel with ok results. But today, I exclusively run springs made with 9000 series spring steel. They are more expensive & worth every dollar.

Springs made out of common, cheap spring steel will seem lazy. Springs made with 4000, 5000 or 9000 series spring steel exhibit better "stored energy" when compressed ... and react quicker. In my experience, 5000 reacts better than 4000, and 9000 better than everything else.

If you take a race car and put the correct rate springs in all four corners, of low quality spring steel, the car will be lazy. The car will react slower. If you replace the springs with high quality springs of 4000, 5000 or 9000 series steel, with the same spring rates ... the car will be more responsive. The bottom line is the quality of spring matters to the performance of a race or track car.

Engine valvetrain experts learned this with Spintron testing, where they can see how different quality of valve springs ... with the same "rate" behave differently when trying to follow aggressive cam lobe profiles. Lazy springs don't keep the lifter attached to the cam lobe as well, and "float" easier. Higher quality springs follow the camshaft lobe shape much better.

The same concept exists in suspensions. Lower quality springs are not as responsive to track surface irregularities and don't keep the tires in contact with the track surface as well. Higher quality springs are more responsive ... quicker to respond ... and therefore react to track surface irregularities better and keep all four tires' contact patches in contact with the track surface more. This equates to increased tire grip ... and speed. I have tested this in race cars where we simply swapped in the same rate of springs at the exact same heights & corner weights (scales & digital calipers utilized) ... on the same track with the same driver. The driver comes back after running the new springs (9000 series) and says, "Wow. I don't understand it, but the car has more grip, feels better and is more responsive to input." I say, "Yeah, I know. And it went 2/10 quicker on the stop watch."

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17. Coil Binding Strategy
I'm changing topics slightly, but it comes back around to springs.
Initially NASCAR Cup teams utilized bump stops to control the travel & stop points in high travel/low roll front suspensions, like I outlined in post #287. When NASCAR outlawed bump stops for a period of time, creative crew chiefs & engineers were not about to give up this performance advantage, so the concept of coil binding springs was born & developed.

Coil binding a suspension ... correctly ... is very challenging. Here is why. You need to get the spring to ...
• Hold the car up to the proper ride height within .030"
• Compress at the proper rate under braking
• Coil bind at the exact height needed within .030"
• No room for error ... or the car handling would go out to lunch
• Coil bind straight without bowing or bulging
• Coil bind over 1000 cycles of a typical NASCAR weekend without failing, losing rate, height or shape

Ahhh ... wow. Initially this was a can of worms, and led to a micro industry for spring companies custom building one-off springs to extreme exacting standards. Aside from getting super accurate dimensions, the other problem was, when standard quality springs achieved coil bind, they failed. They lost height, rate, shape of some combination. When it happened during a race, as it did, that car went to handling like crap and there was no "tuning adjustment" going to fix it.

All of this took a lot of trial & error, engineering & re-engineering, testing, development, etc., etc. Eventually, a few companies got it dialed in to where the spring material and manufacturing processes produced a high enough quality spring that it could coil bind over 1000 times a weekend, survive, hold shape, height & rate. They got the design & spring winding procedures down to the point that crew chiefs & engineers could order springs with "end result detail" like rate, height at rest with a specific car corner weight load & coil bind height. These springs cost $1500 each, or $3000 for a pair of fronts. Top teams use them one race & dispose of them.

Coil-binding is an expensive, challenging and non-forgiving set-up strategy. I've done it & won with it. But no one in their right mind prefers coil-bind over using bump stops. Bump stops are inexpensive, much easier to tune & forgiving to a much larger degree. If we have the option to run bump stops ... I almost always do. With the introduction of the COT & then the Gen-6 car, NASCAR changed the rules up to allow bump stops again. Hallelujah !!! This was a major cost cutting rule change welcomed with open arms.

I shared the story about coil-bind suspensions for three reasons ...
1. So you know why it was used in the first place.
2. So you know not to go down that path if you have options.
3. Because some important revelations were learned during that era.

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18. Energy & Grip Loss
For decades engineers couldn't explain why a percentage of tire load (and therefore grip) was lost during body roll. Engineers just accepted that a percentage of load transfer on the tires ... side to side, front to rear or any combination ... would be lost. Could be anywhere from 5-10% load loss. Meaning we weren't loading the tires 100%. Lost grip.

When Racers & Engineers started using 7-post "shaker rigs" to test suspension loading, everything came to light. Regular sprung race cars (no coil-bind or bump stops) showed the load transfer loss we came to accept. When they tested race cars utilizing coil-bind strategies, where the spring is completely collapsed & basically solid steel, the load transfer (grip) jumped up to 99.8%. Almost 100%. The .2% is suspension flex. We now know that lost percentage of load transfer is due to energy loss through the spring wire.

Upon testing more race cars on the 7-post with regular setups (not coil-bind or bump stop) ... testing showed the length of the wire that makes up the coil spring affects the net load & grip result. The longer the wire is in a spring, the more energy loss, and load loss, there is. Less grip. Conversely, the shorter the wire is in a spring, the less energy loss, and load loss, there is.

Since then, spring companies now make coil springs with less wire. A 12" x 2.5" ID 500# coil-over spring from 25 years ago had 10-11 coils. Today, race spring companies make that same 12" x 2.5" ID 500# coil-over spring with 7-8 coils. You can see the larger spacing between coils. Veteran racers can feel more grip & the stop watch shows measurably faster lap times. This requires higher grade spring wire & better spring manufacturing processes. So today, we run the shortest wire spring we can that achieves our rate & target amount of travel.

As far as spring heights go ... This is going to sound a little basic ... but goal #1 is to insure we can achieve the target travel without bottoming out. I want to do that with the shortest spring & least coils I can run to minimize energy loss. With a low quality spring ... using low quality spring steel ... this requires more coils and/or thicker coils ... making for a taller Static spring height. Utilizing a high quality spring ... with high quality 9000 series spring steel ... requires less coils and/or thinner coils ... making for a shorter Static spring height.

Back on the 7-post shaker rigs, Race Engineers learned about tire loading with bump stops. The key take away is bump stops are almost as efficient as coil-bind. Almost. Plus, they are less expensive, more forgiving on track, easily tunable & provide good feedback to the driver.

This is good, since 90% of race drivers, crew chiefs & team owners hate coil-bind strategies. Coil-bind springs are $2000 each. They have to "stack" within .020" precision or you have problems. If you change your setup slightly, you have to buy new springs. They feel horrible in the car, since the suspension is basically solid metal. The only give is the tire sidewall.

Bump stops come in a wide range of hardnesses & spring rates. The harder the bump stop is, the quicker the rate comes up & the more efficient it is (less load & grip loss). But it is less forgiving in the car. The rate comes up slower in softer bump stops, so the feel improves & the car is more forgiving. But we lose some efficiency & experience more load & grip loss.

In sportsman racing, we run the stiffest bump stop the track & driver will tolerate. In pro racing we ignore the driver's complaints of harshness. On smooth tracks, we run the stiffest bump stops, have the highest grip & run faster lap times. Rougher tracks require us to back off to softer bump stops. Otherwise, the front end will skip over the undulations in the track surface. We want to be as aggressive with bump stop rate as we can, without upsetting the car.

From this, three other revelations came, that are more important to you & me, since we're
avoiding coil bind. They are ...
1. Energy dissipation through springs, suspension flex, bushings, etc. ... reduces the net loading of the tires.
2. The length of the wire used in making a spring directly affects its energy dissipation characteristics ... and grip to the tires.
3. The hardness of a bump stop directly affects its energy dissipation characteristics... and grip to the tires.

I'll expand on each of these, but in a different order ...

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19. Modern Spring Technology
The amount of energy lost or "dissipated" ... through the springs ... is directed related to how long the spring wire is. The more wire required ... the more energy lost. For years, if a spring had a rate of 500#, the amount of wire to make it was the same from brand to brand ... because for years all automotive spring manufacturers, racing & oem, made springs from the same cheap spring steel.

But automotive spring technology ... which was stagnant for years ... has come a long, long way in the last 20 years.

Today, the spring companies on the leading edge, have learned better processes and use higher grade (and more costly) materials to produce springs that last longer, don't sag, settle or deform ... and use less coils to achieve the same rate. These springs have less energy dissipation than older design, cheaper springs made with inferior metal & processes. That means they apply more net load on the front tires ... for more grip ... during braking & cornering.

How much more? To know that, we'd have to know how much energy was being lost/dissipated through your current suspension, which is beyond my scope. But the simple math is this:
• A 500# spring of old design & cheap spring steel ... with dimensions of 5-1/2" od x 10" tall with ½" wire ... requires 9 full coils (approximately 141" of spring wire). That is 141" that energy dissipates through.
• Comparing to a new design spring, with higher quality steel ... in the same size ... but requiring only 6 full coils ... takes approximately 94" of spring wire. That is 1/3 less wire ... 1/3 less energy dissipation ... and 1/3 less grip lost.

How do you know the quality of springs?
Visually, you can see a higher quality spring takes less coils and has more gap between the coils ... when comparing the same rate & size. (See photo below for example.) But that's only part of the equation. Material is key, so ask what they're made with. A simple rule of thumb is the higher the number, the higher the quality. Where 4000 series steel was a step up 10 years ago, it is low end today. 5000 series work better, and 9000 series outshines them all.

A spring doesn't have to coil bind to fail. Low quality automotive springs fail in some form or another ... from too much dynamic loading or simply from over use (cycles). High travel suspension set-ups with softer front springs work & test those softer rate springs much harder than stiffer springs see in low travel set-ups. I know from my racing experience ... running soft front springs, in heavy track cars ... transferring a lot of load onto the springs with high g-forces from braking & cornering ...
lap-after-lap ... works these soft springs much, much harder.

Most common quality & brands of racing springs being ran ... failed. They failed in different ways. Some would lose height. Some would lose rate. Some would lose shape & distort. Some would do a combination of two or all three things. When springs lose rate, height or shape ... they have failed ... and no longer behave the same way. That's worth repeating. If a spring changes it shape, height or rate, it has failed and will not perform the same.

It is hard for most of our brains to get wrapped around this concept ... that springs can have a given rate ... and yet not act the same. But this is fact. If a 350# spring loses height, but still tests at 350# in a spring rater ... what's wrong with that? It has failed. To lose height, the spring coils must "bend" or "distort" to some degree. They will never act the same. The responsiveness will decrease. We call this a "dead spring."

In my NASCAR Modifieds, when we tried running 4000 series springs, they would fail before the weekend was over. Some would distort, which was easy to see. Some would lose height, which could be determined by measuring the car height. If a corner on the car "sagged" ... we would remove the spring & measure its "free height." Sure enough, it has lost free height. Toss it.

The 5000 series springs were good for 3 races. But the 9000 series springs held rate, shape & height all season and were still perfect after a season of racing. They cost 3 times as much, but well worth it in my opinion. Just for reference, typical 4000 series oval track racing springs cost $50-60, 5000 series springs were $100 & 9000 series springs were $150-175.

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When a suspension has fully compressed & loaded a bump stop ... the energy dissipation decreases substantially ... increasing front tire grip. The energy dissipation doesn't go to zero, like coil bind does, so it doesn't have quite the load & grip a coil bind set-up does. But it's close. How close is directed related to how hard the bump stop is.

The harder the bump stop is, the less grip energy lost. For this reason, pros use harder bump stops, which are less forgiving and act closer to coil bind setups. Less experienced tuners prefer to use softer bump stops, so they have a wider sweet spot range and a more forgiving suspension. Even with the softest bump stops ... the energy dissipation is very low ... and the load & grip on the tire is much higher ... than a spring only set-up.

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The springs are not the only thing in a front suspension that can cause energy dissipation leading to less load & grip. Suspension bushings, if used, cause a lot of energy dissipation. Rubber is the worst offender and harder bushings less so. Race suspensions with rod ends or mono balls have minimal energy dissipation. For the autocross, pro-touring, track car guys, you need to decide where your priorities are & chose accordingly. Is reducing NVH important to you or is getting every last bit of grip more important. It is a tradeoff for sure.

Suspension component flex under load can be another source of energy dissipation, but a minor one. If you have upper and/or lower control arms flexing, I'd be more concerned about the negative geometry changes that occur than energy dissipation. Ideally, you want to utilize upper and lower control arms that are just strong enough to minimize flex and yet still light enough for optimum suspension control & responsiveness.

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Summary:
• Springs with modern technology & high quality steel ... with less wire ... have less energy dissipation
... and load the tires more, providing more front end grip.
• Springs with modern technology & high quality steel ... handle higher dynamic loads & cycling ...
without failing, losing rate, height or shape.
• Control arm bushings & suspension component flex figure into energy dissipation ... and effect tire
loading & grip too.
• Running bump stops achieves almost zero energy dissipation from the spring ... and loads the tires
even more, providing the highest front end grip this side of coil bind.
• Combining bump stops ... with springs of modern technology & high quality steel ... in a high
travel/low roll set-up ... produces the optimum cornering performance available with current
technology.


 
What's the Big Deal with Draco Springs?
There are many grades of spring steel, just like there are several grades of steel used in sway bars. The concept is the same in both. The better the steel alloy, the quicker the spring or sway bar responds.
 
The common grades are in these spring steel families:
  * 2000 series – Cheapest, low grade, OEMs use
  * 4000 series – Much better grade / twice the cost
  * 5000 series – Better than 4000 series & more expensive
  * 9000 series – The Ultimate Spring Steel / Very Expensive

There is NO SUCH THING as flat asphalt ... it all has small undulations & our suspension needs to respond as much as 5 times in a tenth of a second (at only 68 mph) ... to keep the tires following the asphalt ... to have grip. Otherwise, if the suspension doesn't follow the undulations ... when cornering ... the side G-forces push one end of the car off track as soon as the tires lose grip.



Hypercoil was the innovator in the 90's, being the first to use 4000 series spring steel on Indy Cars. I still use Hypercoil springs in my less hardcore applications. Most "brand name" spring companies use 4000 series spring steel today. Japanese company Swift utilizes 5000 series steel. Good stuff. Only Renton Springs & Draco Springs make car springs out of 9000 series steel at this point. Renton doesn't cater to our market. Primarily NASCAR, Indy & IMSA.



Draco makes 9000 series coil over springs in a wide range of heights & rates for our 2.5" ID coils overs. And they offer them at an amazing price relative to 4000 series springs in the market. We offer Hypercoils as our base coil-over springs and they run $80 each. The Dracos are $110 each up to 12" tall, any rate. So a set of four is only $120 more. That is a lot of track performance & peace of mind for the buck.

For front high travel applications, I only use Draco. Period.

How are they better?
  * No sag. Not less sag. None. Nadda.
  * No deformation. None. Nadda. Not Gonna Happen.
  * No rate loss. Same rate today as in several seasons of racing.
  * Quicker responding suspension = MORE GRIP
  * Quicker reacting supsenion, coming out of a corner or through chicanes = Quicker Lap Times

The only springs that will live through the abuse my race teams put them through are made of 9000 series spring steel. We ran the Draco springs. I can't tell you how long they'll last, because we never had one fail. They cost us more, but lasted basically forever and always performed consistently.  Draco offers a full line of 2.5" ID coil-over springs in lengths from 8" to 14" & rates from 100# to 800#+. For years, Draco springs have been one of my little speed secrets to building better handling, quicker race cars.

When you see purple springs on a car ... those are Dracos. purple is bad ass !

20. Bump Stop Technology
Bump Stops are often clouded in mystery. In reality, there are a simple tuning tool for corner entry under braking. They are simply an additional, progressive spring that engages only when you want more spring rate to load the tire & stop the front end travel.

If you have the right setup, they gently stop the front end dive at your target travel amount. Every Time. This loads the front tires more than non-bump stopped setups AND keeps the rear tires loaded. That consistency grip is confidence inspiring, while allowing the driver to learn, experiment & even make errors ... without costly crashes.

Bump stops increase the wheel rate & load the front tires more than regular setups & keeps the rear tires loaded too. That consistent grip is confidence inspiring, while allowing the driver to learn the track, experiment with deeper braking zones & even make errors, without crashes.

Tuning? If the car is loose on entry under braking & turn in, add more shims. If the car is tight or pushy under braking & turn in, remove shims. Yes, it is that easy if you have the right bump stop rate curve. Ron can provide you with the rate charts for all the air & polyurethane  bump stops we use, as well as set you up with the optimum starting place for air or poly bumps.

FYI: There are 4 common types of bump stops .... cellular foam, polyurethane, small coil spring & air spring. We don't use cellular foam because they lose rate too quickly with use. We don't use small coil springs because they do not have the progressive rate we want. Poly bumps work well, are least expensive, but do need to be replaced. Air bumps are tunable for any progressive rate we need. So, we don't need to stock a range of polys. But they cost more.







On rough tracks we run softer rate bump stops. On smoother tracks, we can run stiffer rate bump stops to gain more grip & quicker lap times. Pro racers looking for every ounce of grip & lap time will run very high rate bump stops, as long as the track is smooth enough.

Another cool tuning strategy for road courses is being able to tune the grip on corner entry of left hand & right hand corners separately. If the car is loose on entry of left hand corners, simply add a shim to the RF. If the car is tight on entry of left hand corners, simply remove a shim in the RF. Just do the opposite on righthand corners to make ALL the corners optimum!

You need to calculate the shock travel (shaft travel) to make sure how much room you have for bumps stops.

The formula is:
A/B = C x Cos x WT =ST
A = The dimension from CL of LCA pivot to CL of lower shock mount.
B = The dimension from CL of LCA pivot to center of tire tread. (not the ball joint)

A/B = C
* Do not square it. That is only for spring rate calculations ... not travel.
Cos = The Cosine factor based on shock angle (I use a chart)
WT = Wheel Travel at the center of the tread
ST = Shock travel at the shaft

For example:
A = 16"
B = 20"
A/B = C = .80
Cos = For a 22° shock angle is .927
WT = Wheel Travel desired = 3.5" max in dive & roll
16" ÷ 20" = .80 x .927 = .7416 x 3.5" = 2.60"
ST = Shock travel at the shaft will be 2.60"

When space is tight on the shock shaft, you also need to know the compressed height of bump stop you're going to use. Obviously this requires knowledge & experience with the corner loads & dyno graphs of bump stops. (We're seeing 1250# to 1550# corner loading). I plan to go over this more in-depth in future posts on this thread.

I have run bump stops with compressed heights short as .35" and as tall as 2". As I mentioned in my energy loss discussion, shorter, harder bump stops provide more grip, but less fudge room. That is what I run on race cars I'm tuning. Of the shorter bump stops I like to run, there are several that the compressed height will be in the range of .35" to .70" range

If we want the ability to switch around & run any of the bump stops in this range, we should allow the full .70". Adding .70" to the 2.60" equals 3.30". For this example application, we would need a minimum of 3.30" of shock shaft showing at ride height.

Don't concern yourself if there is more shaft showing ... that's why they make shims & spacers. Frankly, for our applications, we don't concern ourselves with achieving very much extension travel from ride height. Anything over ½" is wasted, but for good measure, we like to make sure the front end has 1" of extension capability from ride height. Less is ok if we really tie down the front end. It will never see ride height in race conditions, let alone above ride height.

I share more bump stop tuning tips in the Track Tuning for Handling Balance section of this forum website.

21. Modern Sway Bar Materials
Sway Bars made out of common DOM tubing react lazily. In a bar rate tester, they have almost the same rate as better grades of chromoly bars. But they do not react anywhere nearly as quickly as 4130 or better chromoly tubing. Just like springs, sway bars made with higher quality 4130, 4140, 4340 & 300M series steel exhibit better "stored energy" when twisted ... and react quicker. In my experience, 4130 reacts WAY quicker than DOM. 4140 reacts a little quicker than 4130. 4340 reacts a little quicker than 4140. Lastly, 300M reacts quicker than anything, by a significant margin. They're just VERY expensive.

Just like better quality springs, if you take a race car and put the correct rate sway bars front and/or rear, of low quality steel, the car will be lazy. The car will react slower. If you replace the sway bars with high quality sway bars of 4130, 4140, 4340 & especially 300M, with the same rates ... the car will be more responsive. The suspension will react quicker & being more responsive to driver steering input. The race car will follow the undulations of the track better & flat out have more grip. This has been proven at several pro levels of racing.

Off track slightly, but those of you who follow NASCAR may remember a little scandal, when someone from Mike Waltrip Racing stole a sway bar from Roush Racing that was out of the car. Roush was the first team to utilize super thin wall 2" OD sway bars of 300M material. Their cars were had more grip & were simply faster. So, someone at MWR stole a bar so they could figure it out. It eventually was returned, but the stigma stuck with MWR along with their other cheating scandals until the sponsor NAPA said Nope, no more.

They are other treatments that help the bars perform better. One is micro polishing the surface. Another is the right heat treatment after machining, which is very valuable. While I'm on this topic, the optimum heat treatment process can make a huge difference in the life of, and performance of almost all race parts. Of course, the incorrect heat treatment process can do more damage to the part, than help. Heat treatments are a science.

For decades Speedway Engineering had the best rear axles in racing. They used Hy-Tuff brand name steel & a special heat treatment process. It was so good, other axle companies bought Hy-Tuff raw axle blanks from Speedway. I remember when Strange Engineering, a very good company for drag racing stuff, got into the oval track axle business. They boomed right off the bat using Hy-Tuff brand name steel in their axles. But the failure rate put that division out of business for all practical purposes.

They didn't know how to make axles that lasted & handled the abuse like the Speedway Engineering axle could. Or I should say can. Speedway Engineering closed for a bit after almost 50 years. But were bought by a sharp racing business family who have it back open. Production is up to speed for the most part & they have the secret formula for the great rear axles.

The bottom line is the quality of materials & processes on sway bars matters to the performance of a race or track car.

Lower quality sway bars are not as responsive to track surface irregularities and don't keep the tires in contact with the track surface as well. Higher quality sway bars are more responsive ... quicker to respond ... and therefore react to track surface irregularities better and keep all four tires' contact patches in contact with the track surface more. This equates to increased tire grip ... and speed.

In our Race-Warriors, we only use 300M sway bars, for the highest level of racing performance. They are expensive. Where Draco springs with 9000 series steel are only 38% more than Hypercoils with 4000 spring steel ... 300M sway bars are twice the price of 4130 bars. Worth every penny for racing. Not so much for track cars.

How are they better?
  * No rate loss. Same rate today as in several seasons of racing.
  * Quicker responding suspension = MORE GRIP
  * Quicker reacting supsenion, coming out of a corner or through chicanes = Quicker Lap Times

22. Stiff Rear Spring Strategy
Now I'm going to throw a curve ball at you. This is an option for the low-roll suspension strategy. You already know we run bigger front sway bars. The "meaner" the set-up ... and lower the target roll angle ... the larger the front sway bar is ... to reduce the roll angle in front. For the rear, a high rate sway bar
won't work. Anytime the rear sway bar gets too close in rate to the rear springs, the bar lifts the inside rear tire off the ground. Literally.

What works pretty well is having a very adjustable rear sway bar set up, like my RSRT versions with 4 holes 3/4" apart, with the highest rate 55%-60% of the spring rate. If you read in the forum section called "Track Tuning Techniques for Overall Handling Balance" you know how much I love utilizing the rear sway bar as a tool handling balance mid-corner. We just can't get carried away with rate. If the rear springs are 300#, I like the stiffest rear sway bar rate to be 180# or less. Remember, we want to reduce the loading of the inside rear tire mid-corner ... to achieve neutral handling balance. But we don't want to fully unload .. and lift ... the inside rear tire. No sir. Huh-uh. Notta. Nope.

If you choose the low roll strategy & increase the front roll stiffness, you need to increase rear roll resistance to match, or we end up with the problem of having diagonal roll the wrong way, from inside front tire to outside rear tire. You have too good options in the rear. One is soft springs with a higher rear roll center & the second is stiffer rear springs with a lower rear roll center. Ideally, with the appropriate rear sway bar.

How high? Higher than my mind could comprehend the first time I was taught this strategy. I have a story for you. I hired a NASCAR Busch crew chief to learn some things from. Rented the track, flew him out, had 2 race cars & crew to test. We tested with front spring rates, different bump stops & even coil-bind setups in search of some lap time. Found it. Both race cars got quicker throughout the day with changes. In fact, we finished testing everything on our agenda early.

That is when this NASCAR Busch crew chief said he'd like to try some things in the rear if I was open to it. Sure! Heck yeah! You know it! Then he said, "Do you trust me?" I thought that was a weird thing to ask after a day of testing. Good testing. Sure I do. Of course. He went up in our Cup Hauler & started going through springs, looking for a certain rate. I told him he was in the wrong drawer. Those are front spring rates. But he grabbed a pair of 600# springs & headed for the car.

I was like ... hey there ... whacha doin'? Again, he asked if I trust him. Ahhh ... yeah. But ... those are 600# front springs. We were running a set-up with rear springs around the 275# range. When the NASCAR Busch crew chief I was working with said we were going to run 600# rear springs ... it fried my brain. First I thought he was nuts or high. If the car is "loose" with 300# rear springs ... what will it do with 600# rear springs? I said, "This is crazy. It will just spin out. It won't have any grip."

But it was the end of a test day, and we were there to test, so I said "sure" ... and warned my veteran, winning race car driver that this car may feel like driving on ice & to "be careful." We had a race to run in a few days. I asked him to just "sneak up on it." He did. Started off 70% and worked his way up faster each lap. By the end of the session, the car was measurable faster than a few minutes earlier. Same car. Same driver. Same track. 600# rear springs. Hmmm.

The car rolled back into the pits after the run. I looked in the window & asked my Driver if he felt the car was faster through the corners even though it had less grip on exit?  He said, "it had MORE rear grip on exit. In fact, the car had more grip on all 4 tires." The data acquisition & lap times on the stopwatch all matched. My brain was officially fried at this point. With my 20+ years of racing background (then) it didn't make sense. If the race car was good with 275# rear springs, a little loose when we tested 300# springs earlier in the day ... how could it have more rear grip, more total grip ... with 600# rear springs?

Our test day was over. We went to dinner & beers afterwards. I asked him to explain it & he did. The explanation kind of made sense. Kind of. I struggled to wrap my head around it. So, I arranged for him to stay another day, moved his flights & rented the track for the next day, to test this "new strategy"

We went back to the track the next day with the same set-up intact ... with 600# rear springs ... and similar weather (California). Car ran great. As a controlled test ... with full data acquisition & a team of Engineers ... we went down on rear spring rate in steps. The results were:
Session #2:  500# rear springs = Less grip / A little loose
Session #3:  400# rear springs = Crazy loose / Undrivable
Session #4:  350# rear springs = Pretty loose / Not raceable
Session #5:  300# rear springs = More grip / Just a tick free
Session #6:  275# rear springs = Good grip again / Not as good as the 600# springs
Session #7:  600# rear springs = Good grip again / Better grip than the 275# springs

Monitoring the tire temps (infrared sensors behind the tires) showed the concept he explained clearly ... and I got it. I want you to "get it" too. Here is what happened with the tire temps.

Session #1:  600# rear springs = Inner Tire Temp Avg  177° / Outer Tire Temp Average 184°
Session #2:  500# rear springs = Inner Tire Temp Avg  167° / Outer Tire Temp Average 180°
Session #3:  400# rear springs = Inner Tire Temp Avg  147° / Outer Tire Temp Average 168°
Session #4:  350# rear springs = Inner Tire Temp Avg  151° / Outer Tire Temp Average 177°
Session #5:  300# rear springs = Inner Tire Temp Avg  135° / Outer Tire Temp Average 183°
Session #6:  275# rear springs = Inner Tire Temp Avg  124° / Outer Tire Temp Average 191°
Session #7:  600# rear springs = Inner Tire Temp Avg  177° / Outer Tire Temp Average 184°

Again, do your best to visualize what is actually happening in the car "dynamically" mid-corner & exit ... and your understanding can move to a higher level. When the car had 275# rear springs the outside rear tire was loaded just enough for good grip throughout the corner ... and no more. The inside rear tire was, for all intents & purposes, loaded very little during the roll through zone of the corner ... and loaded more on corner exit under throttle. Combined, the grip of both tires was good.

When the crew put 600# rear springs on the car ... the outside rear tire was loaded less (but only a little bit) than it had been & the inside rear tire was loaded a LOT more than it had been ... but combined, they provided a HIGHER amount of total grip through the corner.

Here's the bonus. The outside rear spring (being 600#) helped keep the inside front tire PINNED & LOADED throughout the corner. No matter what direction, the inside tires were loaded more (shown by increased tire temps). This is how the car had more total grip, not just more rear grip. Frankly, had it had ONLY more rear grip, the car would have gotten tight/pushy & slowed down. When, in fact, it got quicker lap times. As the driver said, the total grip improved with the stiffer rear springs.

Now, I left something out of the conversation so far, that we'll address now. Rear roll center height. As you probably know I like panhard bars because I can load them left or right to favor tracks with corners predominantly one direction. We adjusted the rear roll center evenly every session.

Session #1:  600# rear springs = 8.00", 8.25" & 8.50" > 8.25" Best
Session #2:  500# rear springs = Tried 8.25", 7.50" & 9.00" > Not Happy Anywhere > 8.25" Best
Session #3:  400# rear springs = Tried 9.00", 8.00" & 10.00" > Crazy Loose in All 3 Settings
Session #4:  350# rear springs = 10.00", 9.25" & 10.75" > Pretty Loose in all 3 > 10.00" Best
Session #5:  300# rear springs = 10.75", 10.25" & 11.25" > 10.75" Best
Session #6:  275# rear springs = 11.25", 11.50", 11.00" & 10.75" > 11.00" Best
Session #7:  600# rear springs = 9.50", 9.00" & 8.50" > 8.50" Best

Conclusion 1: Even though the soft rear spring with high rear roll center is "Close" in performance to the stiff rear spring & lower rear roll center ... the stiff spring/low roll center combination is faster. I have had it proven to me & others many times in ABA tests. I've seen it on other cars I had nothing to do with in both oval track & road racing.

In 20+/- years I have utilized this "Stiff Spring Strategy" on hundreds of race cars. There are two sweet spots or ranges for rear spring rate & a dead zone. One ... the lower "soft spring" range ... is based on working the outside rear tire primarily. The second higher range ... is based on working both rear tires closer to even. When we combine this with a big sway bar set-up in the front ... that works both front tires more evenly that conventional set-ups ... we have a package that works ALL 4 tires better.

Conclusion 2: There are two sweet spot ranges for rear spring rates & a "dead zone" in between. It is affected by the car's weight, but it's more or less 200# in-between the two sweet spots. From experience I find for cars in the 2500#-2800# range, the soft spring sweet spot is 175# to 275# ... the dead zone is 300# to 475# ... the stiff spring sweet spot range is 500# to 650#. For cars in the 3000#-3500# zone, the soft spring sweet spot is 225# to 350# ... the dead zone is 375# to 575# ... the stiff spring sweet spot range is 650# to 800#. Treat this just as a guideline & do your own testing.

The car has more total grip, is faster through the corners, easier to drive, way more consistent on long runs. All modern race cars in top professional series run a low roll strategy today. No teams are on a high roll set-up. They wouldn't qualify for the field at the top levels of racing. At the grassroots level of sportsman racing & competitions like autocross & track events, high roll set-ups are still the norm, but low roll set-ups are "trickling down" from the pro level to grassroots level.

Reminder: With low travel/high roll setups, utilizing stiff front springs, running the stiff spring strategy is not a great option. The stiff rear springs reduce the roll. If all four springs are stiff the car doesn't want to roll or pitch. So, it kind of skates on the top. This works better if we're lower to the ground, with low CG. But not so great with a significant ride height & higher CG.

With high travel/low roll setups, you have the option of running either soft rear springs with a higher rear roll center ... or the stiff rear spring strategy with the lower rear roll center. The stiff spring strategy is faster, but not without disadvantages. With stiff rear springs, drivers need to crack the throttle softer & then can roll it on relatively aggressively. We do not want to "shock" the rear tires with stiff springs, as they will break loose. Once that happens & they heat up, it's hard to get back to good rear grip.

Softer rear springs absorb some of the shock of a driver aggressive at jumping on the throttle. So, know yourself or your driver & use that in the decision. Another disadvantage is the stiff rear spring strategy does not like rough tracks. Slightly bumpy is fine. Undulations in the track surface are fine. It will still be faster. But I've seen autocross courses where the competitors are driving across a drainage ditch. That's not a good environment for the stiff rear spring strategy.





23. Spring Preloader Strategy
The preloader spring strategy in the rear is pretty simple to do. But it is complex if you didn't read about spring rates, spring load/force earlier & the stiff rear spring strategy just above. If you haven't read those & you find yourself here. Stop & read sections 11, 12 & 22.

Having read section #22, you know how the stiff rear spring strategy produces more front grip AND more rear grip. But what if we could get even more grip on corner exit ... without giving up any grip or speed on corner entry & mid-corner?  This spring preloader in the rear achieves that. Proven on track with many road racers in classes all the way up to Trans Am. Here's how it works.

If we would run a 2.5" ID x 10" 600# rear spring rate ... for our stiff rear spring strategy ... and compress it 1-1/4" ... that's 750# of spring load/force ... to hold up the rear of the car at ride height. On corner entry, as the race car starts to roll & compress the outside spring more, the 600# rate spring is effectively adding 600# per inch.

We're not going to roll a full inch (I hope not anyway). For conversation, in this example, let's say we see 1/2" of compression on that outside spring at max g-load, mid-corner. That 1/2" of compression of the 600# rate spring is effectively adding 300# of load/force, at max g-load, mid-corner.

That plus the 750# load/force we had at ride height tells us we have 1050# of total rear load force, at max g-load, mid-corner. This is a realistic number, as we always see less in the rear from roll, than we do from the front with dive & roll combined. This stiff total load/force helps pin down the inside rear tire & inside front tire, creating more total grip.

Now on corner exit, under acceleration, the rear wants to squat more. But we still have an ultra-stiff 600# per inch spring rate, slowing & reducing that needed pitch angle change. So, grip exit grip is "pretty good", but it could be better. Enter the Preloader device. It has an ID that simulates a 2.5" ID coil-over spring. It fits over the coil-over in place of the 2.5" ID spring. The preloader utilizes 3.0" ID coil-over springs.

With this preloader device, we take a 3.0" ID x 12" 250# spring .... And compressed it 4.2" in the preloader ... to create that same 1050# load/force. The preloader & spring assembly then fits over our coil-over shock, just like a 2.5" ID coil-over spring does. You simply turn the 2.5" coil-over adjuster nuts on the rear shocks until this preloader & spring assembly are snug. Then adjust the race car to the same ride height.

Now, on corner entry & mid-corner, we have that same 1050# of total rear load force. This same stiff total load/force helps pin down the inside rear tire & inside front tire, creating more total grip. In fact, it may be too much. If you find it is too much rear grip, you can raise the rear roll center or utilize less preload. Regardless, when it's time to pick the throttle up, you now have a 250# spring rate in the preloader versus the 600# spring rate in the regular stiff spring strategy. The race car will have SIGNIFICANTLY MORE REAR GRIP on acceleration out of the corner. Combine this with a decoupled 3-Link & really good shocks for the ultimate acceleration rate.



RSRT offers complete 3.0" Spring Preloader Package with Travel Indicators, Spring Retainer Spacers & Upgrade to 3.00" ID Draco Springs. The Travel indicator helps you two ways. One is to confirm how far you are traveling both shocks & springs for calculations sake. The second is to establish a travel baseline like I do. I ALWAYS MEASURE the travel of all four shocks. If it's a coil-over, we know the springs are compressing & extending the exact same. And if the race car has separate shocks & springs, shock travel & math will still tell you how much the springs are compressing & extending.

The second way indicators help you, is if you know how much travel the race car has when it's "happy" ... when the car is unhappy ... you'll know if the car is diving of rolling too much. In the front, if you're on bump stops, indicators can tell you if you are getting on & into the bump stops ... and how far. If you're not on bumps or coil-bind, the indicators will tell you your actual dive travel.

Either way, if the car is unhappy on corner entry, you'll know if you're diving the front end too much or too little. Similar in the rear. If the car is unhappy on corner exit, you can tell if the race car is rolling too much or too little. Frankly, you have to be diligent & disciplined at taking these measurements when handling is good, ok or crap. You'll learn a pattern about your car and your race tracks. You'll find yourself at Whatsamatteru speedway & the car is unhappy. Sure enough, if you check the dive & roll numbers, you'll find you're off from the race car's sweet spot. With this information, you can make an informed tuning decision to get your race car back happy and hauling ass.

24. Modern Shocks & Special Valving



Let's talk shocks:
There are few places we never want to cut corners on with performance & race cars. Along with safety & brakes, shocks are right up there at the top. No other single component can have such a positive impact or negative impact as the shock absorber, aka "Dampers" as they are called in Europe. What a good shock can with the right valving can do for the handling of your race or track car is mind boggling. Check out the story later in the catalog about what we achieved with a GT Endurance Road Racing Team with the right shock and valving changes.

There are a lot of things that affect the total performance of the shock:
Materials & Manufacturing        Diameter of Piston        Quality Control
Piston Design & Weight        Internal Shock Design    Bleed Circuit   
Seals & Surfaces inside        Shock Oils/Fluids        Valving Strategy

As complex as that sounds ... it's really quite simple from my perspective:
  * If the Internal Shock Design is inferior, it doesn't matter what else we do.
  * We can make an inferior shock better or worse than it was, but was not make it a superior shock design.
  * Old Twin Tube design shocks respond in 25-30 milliseconds. That sounds fast, but it's quite slow.
  * Well-designed Monotube Shocks respond in about 5-6 milliseconds. That's FAST.

And we need the shock to be fast responding, because the asphalt surfaces we run on are NOT flat. No track is flat. If you & I grabbed a flashlight & a 10' straight edge & went to the middle of any corner of any race track ... we'd see 4-7 undulations in that 10'. At autocross cornering speeds of only 34 mph, we'd need the suspension ... and the shock CONTROLLING the suspension to respond 4-7 in 2/10 of a second. If not ... your tire is simply skipping from top to top of the undulations.

No issues when the car is straight. But when you're cornering ... as hard & fast as you can ... the instant the tire loses grip, that end of the car takes off toward the outside of the track. On a road course, with a 68 MPH corner, we're asking the shocks to respond twice as quick ... 4-7 times in 1/10 of a second.

In short ... the responsiveness of the shock is critical for grip. For that reason, I do NOT work with, sell or revalve Twin tube shocks. Life is too short to drink cheap beer & race with cheap shocks. Ridetech, Fox, JRI, Ohlins & certain Penske & ARS models are the only shocks I work with currently. Everything else is a waste of time & making your car slower for no good reason.


 
You don't have to spend a fortune on shocks. Stay within your budget. But pass on buying the chrome, double polished, whiz bang unobtanium valve ... and get yourself some good shocks. The difference in grip is night & day. Regardless of talent or experience, you will be amazed at the additional grip. Grip is your friend. Grip is safe speed.

As far as my trick valving goes, I have done it in twin tube shocks when we raced in cost controlled series that didn't allow monotube shocks. But we cannot get anywhere near as aggressive with the valving, because twin tube shocks will lock up & skip over the undulations in the asphalt surface. (No asphalt is flat. Nada. None. All asphalt tracks have undulations)

For example, the meanest I can get with what we call "zero number" in a typical twin tube ... and keep the shock on the ground ... is about 150#. Where in a monotube, we run from 400# to 1200# often. Ridetech, Fox, Ohlin, Penske & JRI shocks with my valving are only available through RSRT & my dealers.



Single adjustable monotube shocks are the great "grip" bang for your buck. Adding a base valve to the shock internals reduces the shaft pressure, decreases response time & increases grip for a modest cost. Great value. Going to double or triple adjustable shocks with a canister does the same thing as the base valve, but a smidge better. Cost is more.

The extra adjustments don't add grip by themselves. They just make it easier to dial your car in to varying track conditions. Worth it?  Depends on your goals versus your budget. We run the triples when we have the budget. They are a little better responding & performing (5.5ms vs 6.0ms) but is that worth more than double?  Not unless every lit bit of performance is valuable to you. That last little gain of grip is small, but it's expensive.

With all our shocks, we include:
  * The dyno sheet showing your shocks valving front & rear
  * A quick 5-Point Guide on how to understand the dyno sheet
  * A baseline setup ... a tuning guide ... and my cell number to call me from the track for tuning advice

Shocks are the final frontier to making cars have more grip to brake, corner & accelerate better & faster. One of the most important measurements of a shock ... and the least talked about by average car guys ... is its response time from input to control.

From small inputs, like minor track surface irregularities to larger inputs, like bumps, how quick a shock responds IS the most important key. It does not matter what your shock valving is ... or that it is adjustable ... if the tire isn't loaded on the track surface! For this reason, any design technology that makes a shock respond quicker, is valuable ... and slow responding shock designs are not acceptable for winning track performance.

The first important choice you'll make is between "Hydraulic Twin Tube" or "Gas Charged Monotube". It's not really a debate. Twin tube shocks respond in the 20-30 millisecond range & monotube shocks respond in the 5-6 millisecond range. That is a HUGE difference!

Running twin tube shocks in a race car makes no sense, unless the rules require it. The ARS, Fox, JRI & Penske race shocks we utilize are of the superior monotube design. Testing has shown our ARS valved shocks to be the absolute best for autocross, while our Penske valved shocks dominate on road courses. JRI shocks are the best dual purpose autocross & track shock, but expensive. Our Fox Racing Shocks are very close in grip for 1/3 less money.

Superior, faster responding, higher grip monotube coil-over shocks typically cost $200-300 more than the lower performing twin tube design shocks. Scrimp somewhere else. Buy the monotubes!  Remember: It does not matter what your shock valving is ... or that the valving is adjustable ... if the tire isn't loaded on the track surface!
Shocks are such a critical key to winning performance, the technology evolves very fast. In just 3 years, the technology leaders have changed significantly. The Fox/Ridetech shocks we built for years with digressive pistons & Secret Sauce valving, are still available. But the new Fox Racing Shox are significantly better, at similar great pricing to Ridetech.

As of 2026, JRI shocks have not progressed much the last few years, but still offers their same high grip technology & digressive valving. ARS & Penske have taken the lead in development with decoupled/digressive pistons that increase grip even further over irregular surfaces on all tracks. Penske now offers their patented "Regressive Valves" that allow the driver to literally drive over road course curbs at speed WITHOUT unsettling the car!

All four race shocks I use (ARS, Fox, JRI & Penske) are available with base valves or canisters to reduce rod pressure & increase grip. The highest grip, most adjustable, single adjustable is new from Fox Racing Shocks. Our testing & results have shown our ARS valved canister shocks to be the absolute best on autocross courses, while our 8300DA & 876TA Penske valved shocks dominate on road courses. JRI shocks are still the best dual purpose autocross & track shock.

As mentioned earlier, shock technologies advance very rapidly. And for good reason. Shocks play such a crucial role to race car handling, tuning, grip & lap times. There is a story in this catalog where I worked with a top GT race team on the West Coast. They were previously champions, but a little behind in their shock program. My newer technology shocks made their GT car 3.5 seconds faster at Button Willow Raceway in California. They went on to win WERC, USTTC & Trans Am championships with that car all on the same shocks.

Autocross has been called road racing in a closet. Everything is shorter straights, corners, chicanes, hairpins, etc. There is less time for the car to react. So, the fastest responding shock has an advantage & running slow reacting shocks is simply dumb. The 3200 series (small body) single adjustable monotube shocks, from Advanced Racing Suspension (ARS) ... react in 5.3 milliseconds (ms). These shocks were designed by Ex-Indy Car racer Corey Fillip, whose shocks are winning in open wheeled & full body race cars all over.

The ARS 3200 series (small body) double adjustable monotube shocks with external canister respond in 4.5 ms. For comparison, the quickest reacting shocks from Fox, JRI & Penske (also with canister) respond in 5.0 ms. Fox, JRI & Penske non-canister shocks respond in 5.5 ms.

So why don't we run these ARS 3200 series (small body) shocks in everything?  The small body & small piston help achieve the quick response. But the shock body, even with canister, doesn't carry enough oil volume for long usage, like road courses. Like everything in life, racing is about pros & cons, as well as finding the best balance for your usage & goals.

Currently, Penske shocks are the leading technology in road racing. The 5.0 ms response time combined with digressive/decoupled pistons make these Penskes the highest grip shocks in road racing. Their 8300 double adjustable & 8760 triple adjustable shocks are winning in everything from IMSA to Indy Car. I worked directly with Penske Engineers to develop our Secret Sauce valving that utilizes tie-down technology in the bleed circuit to create the highest grip valving possible for road race cars with a ride height above 1.5".



Hysteresis:
Hysteresis in shocks is bad. It's bad for grip. Even light hysteresis reduces grip over track undulations. When it's severe, the driver can feel it in the car. It's unnerving. I run all my canister shocks with double or triple adjustments at zero on compression to avoid it.  What is it? And why do we need to pressure balance our shocks? For grip of course!  Penske has a great article that explains it much better than I could. Read on:




 
Front shock valving:
Shock rebound adjustability takes priority over compression adjustability. Why?  Simple. On compression the spring rate & shock compression valving are working together. On rebound the spring rate & rebound vavling are opposing each other.

On compression the shock valving is providing hydraulic resistance that adds to the spring rate, slowing down the rate of compression on that corner of the car. For conversation sake, let's say we have two cars, one with 900# front springs expecting to dive 1 inch under hard braking.

The second car with 300# springs expecting to dive 3 inches under hard braking. If our front shock compression valing provides 50-100# hydraulic resistance, all we were doing is slowing down the rate of compression of that 900# spring over 1 inch or 300# spring over 3 inches.

But on rebound, the shock valving is the ONLY thing slowing the lift (rebound) of that corner of the car. Some racers describe it as the shock & spring are fighting each other in rebound. Again, for example sake, let's utilize those same two cars. Both have 900# of stored spring energy in full dive under hard braking ... just waiting for the driver to release the brakes.

Once the driver releases the brakes that 900# of stored energy from the compressed spring (on each side) wants to pop the front end of the car up instantly. 50-100# hydraulic resistance wouldn't do much to slow that spring "boing!"  LOL 

We need much more rebound resistance in the shocks to control higher rate springs, as well as the ability to adjust this rebound resistance. Now you should realize WHY the rebound valving of the shocks ... and having a wide adjustable range on the rebound valving ... is so important. The shock's rebound valving is the only thing controlling the spring rate coming back up. This is why shock rebound adjustability takes priority over compression adjustability.

Being able to adjust the compression valving over a wide range is valuable, but not as valuable as the rebound adjustability. For this reason, double adjustable shocks are not twice as good for tuning ... as long as our single adjustable shocks are rebound adjustable.

Another key thing to know is increasing the rebound valving is how we create more grip. The front rebound valving rate is how we create more front tire grip mid-corner ... the key to carrying more corner speed.

The goal of dialing in your camber, caster & toe is to achieve the largest tire contact patch possible dynamically, when the car is in pitch & roll, under hard braking & turning in the corner. Forget static settings. Dynamic tire contact patch is our focus. Use tire temps across the tire to guide you on how well you are utilizing the entire contact patch.

Plus, when the car is in dive, your front CG is lower AND more air flow is going over the car, instead of under it. Both of these benefits add front grip. Of course, the lower the car in dive, the lower the CG & the lower volume of airflow getting under the car ... the larger the gain.

But when the driver steps off the brakes, deep into the corner, the stored energy from the compressed front springs pushes the front end up in milliseconds. You instantly have less contact patch & a higher CG. In less than a second, you'll also have more airflow under the front end. All bad. This is why most cars go into a push condition, upon brake release.

Winning Racers learned they could modify the shock bleed circuit to keep the front end "tied down" for a short, controlled time. This allows the driver to get off the brakes earlier & carry much greater mid-corner speed. This time off the brakes & before throttle is called the "roll thru zone." The rest of the time, the shocks work normal. I utilize "tie down" in all of my Secret Sauce shocks for Autocross, Track & Road Racing.



The shock dyno sheet above shows a RSRT Autocross shock with a max of 450# of "Zero Number" which is the "Tie-Down" force. Each of those lines is a different Tie-Down setting ranging from 0# to 450#. All adjusted with the rebound knob on the shock. The shock force resistance tells us how long the front end will be tied down with spring rates we're used to running. Here are the pounds to time info:
o    150#-200# (0.15 to .20 sec) Works Best for Tight Autocross Courses
o    250#-400# (0.25 to .50 sec) Works Best for Fast Autocross Courses

The shock dyno sheet below shows a RSRT Track-Star shock with a max of 1000# of "Zero Number" which is the "Tie-Down" force. Each of those lines is a different Tie-Down setting ranging from 250# to 1000#. All adjusted with the rebound knob on the shock. The shock force resistance tells us how long the front end will be tied down with spring rates we're used to running. Here are the pounds to time info:
o    400-600# (0.50 - 0.90 sec) Works Best for Rough Road Courses
o    600-800# (0.90 - 1.30 sec) Works Best for Average Road Courses
o    800-1000# (1.30 - 1.70 Sec) Works Best for Smooth Road Courses



Rear shock valving:
Shock rebound adjustability takes priority over compression adjustability in the rear as well. I'm about to let a cat out of the bag that usually only top Crew Chiefs & Tuners know. Increased rear rebound valving rate, in the bleed circuit, also increases rear tire grip on corner entry under braking. It holds the rear of the car down longer ... keeping load on the rear tires ... even though the front end has dived under braking.

Stiffer low speed rebound valving in the rear shocks also increases rear tire traction on corner exit (and drag racing for that matter). The stiffer it is, the more it "holds" the load on the tires. The limits to how stiff you can go with this tuning strategy are limited by the corner entry.

The rear shocks extend on corner entry. Stiffening the low speed rebound valving of the rear shocks ... to a degree ... helps slow the load transfer from rear to front. This stiffer low speed rebound valving of the rear shocks helps keep the rear tires gripped up ... so the car is not loose in. this has very little effect on how far the front suspension compresses, because you're tuning the front suspension compression
separately.

BUT ... you can only go so stiff with the low speed rebound valving of the rear shocks ... before you start making the car loose on entry. What happens is the mass of the rear end lifting simply over powers the shocks trying to hold it down and the stiff rebound shocks actually "pull" on the rear tires. This reduces the load on the rear tires too much and the car gets loose on entry. Been there, done that, a zillion times, pushing the limits.

If we get "greedy" & dial in too much rear rebound valving rate, the rear tires will literally lift with the chassis/body as the driver brakes hard into a corner. This unloads the rear tires, making the car loose on entry. So the goal is to run all the rear rebound valving you can, without being loose on entry. It's not anywhere near as much as we can run in the front.



The shock dyno sheet above shows a RSRT Race-Star Rear shock with a max of 350# of "Zero Number" which is the "Tie-Down" force. Each of those lines is a different Tie-Down setting ranging from 0# to 350#. All adjusted with the rebound knob on the shock. The shock force resistance tells us how long the rear axle will be tied down with spring rates we're used to running.

Here are the pounds to time info:
o    0-160# (0.0 - 0.2 sec) Works Best for Autocross
o    80-240# (0.1 - 0.3 sec) Works Best for Road Courses
o    240-350# (0.3- 0.5 sec) Works Best for Road Courses with Aero

Oh ... if you have significant aero downforce in your car, you can run even stiffer valving on the low-speed rebound valving of the rear shocks. This will give you even greater grip & optimum forward bite on corner exit. The aero downforce from the rear wing will allow you to take this much further and not be loose on entry.

Contrary to old school belief, you don't want to run soft rebound valving in the front shocks. Because the corner exit ... is still a corner ... soft front rebound valving allows both shocks to lift easier. This is bad. The inside front shock unloads the inside front tire too soon and that tire loses grip. The car feels like it has more grip. But in reality losing grip in a front tire does not help the car exit better. In fact, it can hurt the exit ... because the inside front suspension lifting up de-wedges the car. Stiffer front shock
valving (not extreme) actually helps hold in the wedge effect.

How far the front suspension extension travels ... and the rate it happens ... is another key to tuning. You're already planning to run a high travel front suspension, so you have the advantage of substantially more front suspension extension travel on corner exit. You do not want that front suspension extension travel to happen all at once, or anywhere near it. If it does ... you have instant grip ... but not lasting grip as you drive out of the corner.

You want that front suspension extension travel to happen progressively ... starting from the time you start throttle roll on ... and topping out somewhere after you have the steering completely unwound and the car is driving completely straight. Too soft of front shock rebound hurts this strategy.

Avoid crutching exit with these:
• Soft rear springs and/or sway bar
• Soft rebound valving on front shocks

Soft rear springs and/or sway bars allow the car to roll more. This higher roll angle unloads the inside tires to a higher degree. Both of them. So, the inside front tire has less grip ... which hurts the car in the middle. And the inside rear tire has less grip on corner exit. We already covered why not to run soft rebound shocks above. Remember, we're not drag racing in a straight line. In road racing, we need to utilize the tuning tools that don't hurt our cornering capabilities.

My philosophy is, you have a lot of effective tuning tools to achieve optimum corner exit grip ... without resorting to soft rear springs & sway bars, nor soft rebound valving in the front shocks. Tune on the primary stuff first ... secondary stuff next ... and avoid the crutches.

The factors that matter most to handling are:
1. Piston design - defines the valving curves possible & responsiveness
2. Piston seal & friction - self explanatory
3. Bleed valving - controls the initial shock responsiveness control
4. Valving control – in most cases a stack of special shims that deflect & define the oil flow through the piston
5. Adjustability range - To tune or adjust for very different situations like track & street
6. Rebound & compression bleed over - how much does one adjustment affect the other valving
7. Body & overall shock design – affects how it manages the pressure, control & responsiveness
8. Stiction (from piston seal & shock bore surface) = pressure required to get the shock to initially respond
9. Internal rod/shaft pressure - affects initial shock responsiveness

I'm sure I left some things out, but you get the idea. Items 1, 2, 3, 4 play the biggest role in the valving curve. Items 5 & 6 define the range & accuracy of tuning. Items 7-9 help define how well the shock can keep the tire gripping the asphalt over irregular surfaces.

Other things matter too, like ...
• Is it rebuildable?
• Is it revalvable?
• Parts availability?
• Tech support?
• Customer service?
• Warranty?
• Return/repair policy?
• And lastly initial purchase price & TCO ... total cost of operation.

The challenge for shocks:
Keeping the tire contact patch on the asphalt ... irregular asphalt ... at speed ... while cornering. This is way more challenging than the average car guy thinks about. Let's say our car is cornering at 68 mph. That means we're covering 10' in just 1/10 of a second ... or 1 foot every 1/100 of a second. If you were to get a 10' straight edge and go lay it on a 10' stretch of asphalt ... any 10' stretch of asphalt ... and look at it from a side view ... you would be surprised at how many undulations there are on the asphalt in just 10'. I've done this in corners on track and counted 5-10 undulations many times. That means the tire needs to go down into the concave section of the asphalt ... and back up ... and back down ... from 5-10 times ... in 1/10 of a second.

Let that sink in. This is clear ... the suspension needs to respond QUICK. This is proven ... the suspension that responds quicker & keeps the tire's contact patches on the asphalt more ... has more grip ... making it easy & safe to go faster. While there are other factors that affect the suspension's ability to respond quickly, if not almost instantly ... the shock is the biggest factor. Shock design is in a constant state of development at all top racing shock companies & pro level race teams. It is a never ending process of getting the shocks to respond quicker & keep the tire contact patch connected over the pavement's irregular surfaces better. JRI is the leader at this point & has been for the last few years.

The solution: Quicker responding shocks (and suspension). What is involved in achieving this?

25. Suspension Stiction
The factors that affect shock response times in a nut shell are:
• Stiction
• Friction
• Weight of moving parts
• Oil Viscosity
• Gas Pressure

Let's take them one at time:
A. Stiction is the force required to get the shock (and/or suspension) to initially respond. I'm sure you've held factory OEM ball joints and felt how hard you have to push to get them to move. That is stiction. When you remove the springs out of your front suspension and push the spindle & control arm assembly to a point & let go ... and it stays there in place ... that is stiction. In oem cars it is caused by rubber or plastic bushings & tight ball joints. It requires a certain force to overcome stiction BEFORE the suspension moves. This stiction makes it harder for the suspension to respond to these 5-10 undulations in a 1/10 of a second. Less stiction ... more responsive suspension ... more grip.

B. Friction is something most everyone understands in a basic form. Friction ... whether it's in the shock, bushings or ball joints ... is drag ... and leads to pressure being required to keep the suspension moving. Less friction ... faster responding suspension ... more grip.

C. Weight is pretty easy to understand. The heavier something is ... the harder it is to accelerate, decelerate & change directions. Or said another way, when forces are applied to a suspension, the heavier suspension responds slower & the lighter suspension responds quicker. In real heavy suspensions ... the suspension can still be responding from one undulation ... while going over 3-5 more. This prevents the tire contact patch from staying connected to the track surface ... so you have an instant loss of grip. If it happens in the front first, the car pushes/understeers. If it happens in the rear first the car get loose/oversteers.

D. Viscosity of shock oil is pretty basic. Thicker oil viscosity in the shock makes the shock internals moves slower. Thinner oils allow the shock internals to move faster. Faster responding shock ... more grip ... more speed.

E. Gas pressure in the shock is your friend & your enemy. For the uninitiated, modern monotube "gas shocks" use nitrogen gas pressure internally. Gas pressurized shocks have a benefit and a challenge. The major benefit of a modern monotube gas charged shock over a conventional, twin tube non-pressurized shock is responsiveness. In twin tube shocks (with no gas pressure) the internal piston has to travel some before the shock fluid creates hydraulic resistance in the piston ... so there is a DELAY is responsiveness. Once the piston gets moving, it can have the same valving control as a monotube shock. But every time it stops ... there will be a delay in control ... and therefore LESS grip.

Gas pressurized shocks have almost instant valving control, because of the gas pressure in the system. How much pressure in the system is a key factor? It takes a certain amount of gas pressure to prevent shock fluid cavitation. The downside is this gas pressure also exerts force on the rod/shaft inside the shock & has to be overcome before the shock moves. This is called rod pressure & it contributes to stiction. Advanced shock designs have led to shocks that work with less gas pressure without experiencing any fluid cavitation. The lower the gas pressure that can be run ... without experiencing cavitation ... the more grip the shock will have. The challenge for shock designers is achieving that low rod pressure while preventing cavitation.

Stiction anywhere in the suspension is a grip killer. Want to increase your grip? Eliminate all stiction in the suspension front & rear. Where are the problems? Ball joints & bushings. How do you find stiction? Simply test the movement. OEM style ball joints are bad with stiction. Simply grab the base in one hand & the stud in your other hand. Now move it. You found the stud took a certain amount of force to break free, before it moved. That's stiction. How many pound did you have to push to get to move?

There are a handful of aftermarket, racing ball joint brands that offer zero stiction. I use Howe ball joints exclusively. They are modular, offer many stud heights & have zero stiction. I was talked into trying one brand of the China imports in our NASCAR Modifieds and broke 2. One cost us a race win. The other caused a nasty crash into the turn 3 concrete wall. Good thing I wasn't standing there. What? Oh, I was standing there. I literally had to run away from the wall as race car pieces flew through fence.

So, we threw that shit in the trash & put all Howe back on. I have NEVER had a Howe ball joint break, with the exception of head on impacts into the concrete wall. None of them ever broke and caused a wreck. Howe won't say what they're made of, but I know metallurgy pretty well. I am confident they are made from 300M steel & NOT heat treated. So, in most impacts, they bend but don't break.

China ball joints are made with stupid cheap steel & hardened a ton. Their hardness prevents wear, but makes them brittle. No thanks. I'm done. Stick with Howe & sleep peacefully.

Control arm bushings are the other killer area. Rubber OEM bushings can be the worst. The rubber grabs & twists before it allows the control arm to move. Changing to polyurethane bushings is like jumping from the frying pan & into the fire. Bad stiction. Stiction slows suspension response time. So, we spent big bucks to buy faster reacting shocks ... but suspension with cheap bushings ... can't follow the small undulations of the race track surface. To me getting the stiction out is a priority, not a let's get around to it.



If you take the wheels & brakes off your front end & the control arms & spindle combination just hang there, that is a clue. Stiction is holding it up. When you push on it, how much force is required to even get it moving. If it takes significant force to break the control arms free, that is lost grip. Fix it. Delrin bushings are "better", but monoball bushings or rod ends are almost the best. Roller bearings are the very best. (See image above)

At RSRT, I use rod ends in most new control arms we sell. Uppers & lowers. The rod end liner has about 1# of stiction new. The liner seats quickly & is zero stiction after just a few uses. At the high end, we have these triangulated long upper control arms that actually use roller bearings in each shaft. Talk about zero stiction!

The goal is to have your front suspension so free of stiction, you can move the control arm & spindle combination with one finger. Same in the rear if you have IRS. With straight axle & linkage suspension, make sure the housing can articulate ... rotate left & right ... then remove the rear axle housing. Make sure all the links move freely. If they are rod ends I suspect they will. If you have any form of bushings it's a crap shoot. But your ultimate goal is to get your front & rear suspensions free to move easily & do their job.

On steering box systems, we use roller bearings, monoballs & precision rod ends in the centerlink & idler shaft. Of course, the tie rods get swapped to tubular racing units with rod ends. All to reduce stiction & friction in the steering. OEM steering linkages basically use smaller ball joints in the Centerlink & both ends of the tie rods. They have a ton of stiction ... force required to make them move ... and high friction ... adding resistance to the steering. This resistance does not help steering feel ... it masks it. Roller bearings, monoballs & precision rod ends allow you to truly feel the tire on track activity, while making the car easier & more precise to steer.

Bonus Tip #1: Not Grip Related > But Increasing Rolling Speed

I'm a fan of bearing spacers & run them often in race car applications. These are adjustable for width & go in between two tapered roller bearings. They allow you to set the preload on the bearings without over torquing them. Frankly, the thrust load is already distributed to both bearings, regardless of running a bearing spacer. A spacer does not increase the thrust load capability of either bearing, so the small, weak outer bearing is still the weak link.



Bearing spacers allow the bearings to be fully tightened and yet have minimal preload & drag. So, they make the rolling friction less. Moreso on straights, because in corners, the bearings are still side loaded. Even with that side load, THE RACE CAR SLOWS DOWN LESS in the roll through zone with bearing spacers. Simply put, they "free up horsepower" by requiring less power to accelerate & achieve speed. We run them in between the rear floater hub bearings too.

This does reduce bearing temperature, which is a cause of a bearing failure. So, they also increase bearing life. it doesn't change the thrust load capacity of the hub bearings, so you still need to get the best ones that your budget allows. Would I suggest you run bearing spacers? Absolutely. They will "help" your bearing, by reducing the heat ... and they help your car by reducing rolling friction.

Bonus Tip #2: Not Grip Related > But Increasing Rolling Speed
I'm a fan of micro polishing gears & bearings. Why? So many key reasons:
1.    They reduce the rolling friction
2.    Therefore, they increase total speed possible
3.    The race car slows down less in the roll through zone
4.    Polished gears & bearings generate less heat & last longer
5.    Polished gears are quieter
6.    Polished gears do not require any "break-in" time or procedure



Bonus Tip #3: Not Grip Related > But Increasing Rolling Speed
I'm a fan of friction reducing coatings. Why? Lot of reasons:
1.    They reduce the rolling friction, similar to bearing spacers & polished gears
2.    Therefore, they increase total speed possible
3.    The race car slows down less in the roll through zone
4.    Friction Coated gears generate less heat & last longer
*The gears below are Moly Koted



Bonus Tip #4: Not Grip Related > But Increasing Rolling Speed
I'm a fan of ProBlend metal treatment. Why? A couple of reasons. If ... if ... if you don't spend the time & money to micro polish gears or have them coated for friction reduction, ProBlend metal treatment is the next best thing. ProBlend is an oil additive, but doesn't treat the oil. The oil is just the carrier of ProBlend to the metals. Once there, ProBlend treats the metal to have lower friction.

1.    ProBlend additives reduce the rolling friction, similar to coatings & polished gears
2.    ProBlend additives increase total speed possible
3.    The race car slows down less in the roll through zone
4.    Gears generate less heat & last longer with ProBlend additives

26. Suspension Bind
The most common mistake Racers make is not checking for suspension bind. Then the car handles bad at the track, usually in ways that don't make sense initially.

An autocross client had a professional shop install his new Speedtech front clip, front & rear suspension. It would drive "OK" at lower speeds, but when driven fast, all four tires would break away & drift. When he explained this, Ron told him the suspension is bound up. "No way. They were a Professional Shop" and other reasons were suggested. When he inspected it himself, all the suspension was bolted (impacted) into WAY too tight & bound up.

When he removed the coil-overs, the front control arm assemblies and the rear suspension would not move freely. This KILLS grip. Before your car leaves the shop, remove the wheels, coil-overs & one link on each sway bar. Each control arm assembly needs to freely move up & down throughout the useful travel range. The rear axle needs to go up & down, plus articulate freely. Then, with a helper, check it all with the sway bars attached.



Sway bars binding up is super common. We had a Racer run zero gap on each side of his splined sway bars front & rear. The car handled OK at lower speeds. But, at higher speeds & roll angle, the car lost total grip. News Flash:  Sway bars (and torsion bars) get shorter as they twist. His sway bars were binding & shooting the rates to infinity. He added gap on each side & the car handled great.

Another client built his tube chassis car from scratch, but didn't check for suspension bind. He had sway bar linkage binding against the lower control arms. With a Monster 1-3/4" GT/NASCAR sway bar ... it literally broke the lower control arms ... under hard braking. Another sway bar bind situation I ran into was the racer was using typical bronze lined pillowblock bushings.



As you can see from the photo above, the bronze bushings are made for rotation of the sway bar, but side-to-side articulation. These work "OK" if you have zero flex in the chassis. But if the chassis flexes, they will bind up. That is eaxactly what this racer did. The solution is to pillow block bushings with a monoball in it to rotate any direction. See our Delrin monoball bushings below. They will allow the sway bar to operate bind free, regardless of any frame flex.



27. Chassis Flex
When you think about it, all chassis are rigid or flexible to some degree. No chassis is 100% rigid with zero flex, and if it is, you built it waaaaaaay too heavy. Rigidity in a chassis makes the car more responsive to driver input & tuning changes & creates more grip. Flexibility in a chassis makes the car less responsive to driver input & tuning changes ... and has less grip.

The lower grip is due to energy loss from the chassis flexing too much. I use an electrical analogy. Think about if we plug in a super heavy gage wire extension cord, going only 10'. It will not see very much amperage loss, if any. Now make that extension cord 100' & the amperage loss is measurable. Now replace that extension cord with a very small gage wire. The amperage loss will be huge. This is energy loss due to an inferior structure.

Race cars are the same. Most production cars are limp noodles & flex way too much. Some race cars are over designed & too rigid for their application. I've had cars that were too flexible. It was hard to make them fast due to their lack of grip. The flexy chassis just gave up too much grip to be fast. I've had race cars that were too rigid.

When I got into USAC Midget racing, I bought a used race car. I could see it was a more rigid design than others. Man, that thing was fast!  For 10 laps. It was TOO SENSITIVE. As the track would rubber up on a 30-50 lap race, this car's handling would change significantly. We had to decide which 10 laps we wanted that car fastest. LOL

Our biggest competitor in the USAC Midget chassis business had a little trick up his sleeve. I could see the difference between his "House Car" & his customer cars. His cars had additional bracing to be more rigid. When I asked him about it, he grinned & said, "My customers are not constant tuners like you & I are. By making my customer cars softer, the car is less sensitive. It works OK at most tracks & track changes don't affect it as much. I make mine stiffer, which requires being more spot on the setup, but our car is faster."

Our 23 AutoX & Track-Warrior chassis vary in rigidity, depending upon how much power, tire, weight & g-force loads they're designed for ... and what is the priority ... a wide tuning widow -OR- every bit of lap time possible. It's not a one-size fits all. The same can be said for our 8 Race-Warrior chassis. They vary from each other based on power, tire, weight & g-force loads. All 4 of these chassis are designed for 700HP, but very different applications, different g-loads & different goals.

See the 4 chassis images below. The first one is called our AutoX-Ninja. Ninja because it's light & quick. It provides just enough rigidity for a 2600-2800# featherweight autocross car with 700HP. It has no place on a road course. It does NOT provide enough safety in my race car designer opinion. Nor does it have enough rigidity to handle road course g-forces.



The second image, right below here, is our AXT-Warrior, designed for double duty track days & autocross. Same frame. Much safer roll cage design for the higher speeds seen on road courses. This chassis is also designed for 700HP, but more rigid to handle road course level g-forces in the 1.7 range. Compare details.



Compare the AXT-Warrior above to a Track-Warrior chassis below, designed to a full time track car or budget road race car with up to 700HP. The additions in structure are to make the Track-Warrior both faster & safer at g-loads near 2.0g. If all things were equal, weight, aero, power, etc. ... the Track-Warrior chassis will run faster lap times, but have a narrower tuning range than the AXT-Warrior.



Now, below is a full blown Race-Warrior chassis, also meant for 700HP in top level road racing. Very different level of rigidity designed in. It is extremely stiff. Designed for loads well over 2g. This is meant for pro level road racing where every tenth of a second is precious. If all things were equal, weight, aero, power, etc. ... the Race-Warrior chassis will run faster lap times, but have a narrower tuning range than the Track-Warrior.



Summary: There is more detail & information on this area in the forum thread "suspension Strategies for Track & Racing." The key thing to know is if the chassis is too soft, too flexible, you will be giving up some grip. Conversely, if the chassis is too stiff, too rigid, it will have high grip, but in a narrow tuning range. Your goal is to have a race car chassis rigid enough to be fast & flexible enough to have a managable tuning sweet spot.

 
28. Aero Downforce
It feels kind of silly needing to talk about achieving grip with downforce in this section. So I'll keep it simple here & you can read in more depth & detail on how to do this in the "Designing & Tuning Aerodynamics" forum thread on this website.

Remember increasing front grip from aero downforce is just as important, if not more important, than the increasing rear grip with aero downforce. It's easier to get high amounts of additional grip on the rear tires by simply buying & installing a big ol wang or big spoiler. Easy peasy.



If you're not 100% clear on how spoilers work to create downforce, here it is. The spoiler itself is not where the downforce is. The spoiler just slows the airflow over the back of the race car to create a high pressure area in front of the spoiler. The trunk or decklid, as most call it. The flat area is where the downforce is created. The taller the spoiler and/or the steeper the angle of the spoiler defines how high the pressure area is.

The size of the usuable flat surface area plays a role in the rear downforce. The degree of high pressure & the amount of square inches of usuable surface area together define the actual rear downforce. So, a larger and/or flatter trunk or deck lid can create more downforce, if the high pressure created is the same.


 
The trunk/decklid needs to be strong enough to not flex away the downforce. Just like energy loss in chassis, springs & other areas, if the body panel the airflow is pushing on FLEXES, it is not going to be 100% efficient or effective. I've seen body panels flex up to 75 pounds before the chassis moved one iota. Nothing. That 75# of flex is 75# of downforce lost. So we need rigidity in the body panels we're creating downforce on.

Wings are different animals. The downforce is created on the top of the wing surface. So more surface area (of the same wing shape) creates more downforce. The shape of the wing itself plays a big role in both downforce & drag. The closer to flat the top of the wing is, the less downforce & less drag. The more the middle of the wing cord dips down, assuming the design is good, the more downforce & drag created.



AoA, Angle of Attack plays a a key part in how much downforce a wing can make. Basically, for most wings, if the top of the wing cord is level, that will be the lowest downforce & drag position. As you increase the angle of the wing (AoA) the downforce & drag will increase ... up to a point. Every wing shape has a specific stall angle. With each wing shape, there is an AoA in which the downforce stops increasing, but the drag increases continue.

The front is harder. Increasing front grip from aero downforce is a lot more work. Well, getting some downforce in the front is easy. Getting enough front downforce can be challenging. The easy part in the front is building an airdam, then adding a splitter. The height of the airdam/splitter combination needs to work with your suspension travel strategy. The longer the splitter is, going out & forward, the more surface area it has for high pressure to push down on it. You'll notice strut braces on splitters in the photo. Anytime the splitter is more than a couple inches, the downforce will bend them down, losing some of your downforce to energy loss & probably losing a splitter to the track.



Of course we have to create this high pressure zone. The best is an air dam that is either straight up or angled inward to "catch" the air flow in the front. We literally want to stall the airflow here to create a high pressure zone, to push down on the splitter. (See yellow car below) This is not the place to pull engine or brake cooling from, if you want maximum front downforce. (See white car below)



The harder part, but very important is creating downforce over the hood of the car. How well the airflow in the front area of the car flows over the hood is dependant on a few things. First is the smooth roundness of the top of the nose, where it meets the hood. If the top of the nose is not smooth & round, we will see less airflow at the front of the hood. This means we're only utilizing the rear portion of the hood, as airflow gets on it.

The hood surface area has similar needs to the deck lid in the rear. The flat area is where the downforce is created. What's different is the windsheild is our spoiler. The windsheild is what slows the airflow to create a high pressure zone on the hood of our race car. The taller the windshieild and/or the steeper the angle of the windsheild defines how high the pressure area is.



The size of the usuable flat or concave hood surface area plays a role in the front downforce. The degree of high pressure & the amount of square inches of usuable surface area together define the actual front downforce at the hood. So, a larger, flatter & cleaner hood can create more downforce, if the high pressure created is the same. Look at the shear size & surface area of the hood on the yellow Mustang above.

The hood needs to be supported enough to not flex away the downforce. Just like energy loss in chassis, springs & other areas, if the hood the airflow is pushing on FLEXES, it is not going to be 100% efficient or effective. I've seen hoods flex up to 120 pounds before the chassis moved one iota. Nothing. That 120# of flex is 120# of downforce lost. So we need rigidity in the body panels we're creating downforce on.

What hurts smooth airflow over the hood, & takes away downforce, are obstacles to airflow on the hood. Funky shaped hood scoops, Injectors or air filters & other odd obstructions all create trubulence & reduce downforce on the hood. Vents typically (not always) reduce downforce, but are sometimes necessary regardless. I am a fan of well designed vents over the tops of the front tires, if the car has a smooth belly pan. This helps get some of that turbulent air out of the wheelwell. If the car doesn't have a full belly pan, I haven't seen much gain form vents. Mainly downforce loss.

Radiator ducting through the hood may, or may not, reduce downforce. It is a gain/loss situation, where we're hoping to gain more than we lose. I see a lot of homemade radiator ducting coming out of hoods. I realize some do it for cool factor. Some do it better cool the engine. Some do it thinking they're increasing downforce, but most fail at this.

Yes, creating a clean pathway for the airflow to go through the radiator, up & out the hood DOES provide some downforce. The question of loss we have is how much of the downforce the hood makes, was lost from this disruption in the hood's airflow surface. IF, the airflow coming up & out of the hood ducts crashes into the over hood airflow, frankly we'll create more trubulence & a higher downforce loss than we gained from the radiator hood ducting.

My friend Joey Hand raced for BMW for awhile before going to Ford & winning the 24 Hours of Daytona, 12 Hours of Sebring, 24 Hours of Lemans & much, much more in Grand Am & IMSA. So I follow his racing somewhat. The BMW's he raced utlized radiator ducting through the hood. I was told the aero engineers spent days with several hood & duct models in the wind tunnel working it out. What they landed on blended the radiator ducted airflow onto the hood & windsheild very smoothly. It is my opinion, to do this well, and expect to see a downforce increase, requires some pretty smart people & a wind tunnel. Otherwise you just guessing.





Having said that, I prefer to incorporate well designed side vents into the front fenders to evacuate hot air out of the radiator, engine compartment & tire wheelwell. It requires a radical fender rework  to achieve this (see Callaway C7 be3low) but it leaves the full hood open as a downforce platform.



Canards on the leading edge of the front fenders are a nice addition to add some downforce. Most are small & offer small gains, but it still a measurable gain for the front. They help create some front downforce, & if effective, get the airflow out & away from the tires. (See red car below) There is a LOT more to learn in the Designing & Tuning Aerodynamics forum thread.



29. Aero Lift
Reducing lift under the bottom of the race car is just as effective as increasing downforce over the top. In most cases with full bodied race cars, there is NOT as much downforce to be found under the car, as over. But it all adds up.

First, and most important is a full belly pan under the car. Without it, you have a mess under there. Visualize this. In your mind, flip the non belly pan race car over and ask yourself how smooth the airflow will be over that mess? Hell there are crossmembers running perpendicular to the race car centeline. Ok, flip the car rightside up.



All of the obstacles under your race car are slowing down airflow, creating a high pressure zone. This high pressure is pushing UP on the , hood, floorboard & truck area of your race car, creating lift. Obviously, lift is the opposite of downforce. Not good. If you can, if your rules allow, you will see a nice lift reduction, or downforce increase, based on your point of view, from running a full, smooth belly pan.

Next would be building & running an effective rear diffuser. The diffuser's role is to speed up the airflow as it exits the back of the car AND to help this airflow BLEND into the airflow over the race car. In my experience there will be turbulence & drag were the airflow under the car meets the airflow over the car. We're not going to eliminate it. But we can reduce it.

Most diffusers ... I said most, LOL ... on OEM cars are for looks. They don't work for shit. The most effective diffusers are long, wide & arch up in a GENTLE curve like the image below on the left. The one on the right with a flat surface you angle up will be effective. Just not as much as the gentle curved unit. But I'd much rather have a long, straight diffuser than a short one with an aggressive curve. The airflow won't follow an aggressive curve, so that type of diffuser is barely effective if at all.


 
A smooth belly pan, leading into a well designed rear diffuser will reduce the turbulence at the back of the car. This reduction in turbulence is also a reduction in aero drag. So the race car also picks up straight away speed. Bonus.



If you are going to do the full Monty with a full, smooth belly pan & well designed rear diffuser, you should modify your front splitter design. It needs to step up in the middle. (See image below) It needs to have a short, but wide, opening right in the middle, to force a small amount of ariflow through it, to the belly pan. This creates a venturi tunnel of sorts, and will make the belly pan & diffuser MORE EFFECTIVE, than simply running a regular splitter that blocks off air.



On the other hand, if you're NOT running a diffuser, even with a belly pan, a straight splitter that blocks off the airflow works better. You may like the look of the newer "Stepped" splitter. But it only adds downforce when paired with a full belly pan & diffuser.

A key area to reduce lift was mentioned above in the Aero Downforce section. That is venting out the hot, high airflow coming into the engine compartment & through the radiator. If not vented, this will literally create a high pressure are pushing up on the hood, taking away front downforce. Not good. Radiator extractors ducting through the hood can be challenging to get aero effective. I am more a fan of side airflow extractors, that blend into the side airflow, which we're not using much, if at all.

Another great tool to reduce lift are "Ground Effects" we started seeing in the 1980's or side splitters, we often see on modern sports cars like Corvettes. Both have the same goal, to solve a problem. The problem is the curved body panels on the sides of production cars. This is really prominent in cars from the 60's to the 90's, where you see the beltline of the car is the widest point.



Look at your door. If you look down the side of the car, it's clear the body curves under, at the beltline. What this means to us is the airflow going down both sides of the car is ROLLING UNDER the car, from the beltline down. Ground effects we're designed to attach to the rolled under doors & fenders to stop this. Most, if well designed, actually rolled out at the bottom edge. This was to give the airflow a "lane" to flow down the side of the car & not under.

More modern cars are built with much less rolled doors & fenders. Many incorporate what would be considered smaller ground effects. They are basically a lip to prevent the side airflow from rolling under. C5 through C7 Corvettes have a small roll under area. But many of the performance packges include side skirts. They basically a short panel that stick out a bit, stopping that airflow rolling under. All to stop lift. Aftermarket "side skirt" kits exist for many newer cars. But if you're building a track or race car, you can make this. Wider is better.

30. Aero Sideforce
Sideforce is something you rarely hear about outside professional racing circles. But in all of pro racing, the aerodynamicists pay attention to sideforce as well as lift & downforce. What is it? Well ... it's aero force generated on the side of the race car, near the rear quarter panel. It is airflow pushing on a flat-ish surface, when the driver turns the race car into the corner at speed. The car is in yaw, relative to airflow, so there is more outflow on the outside of the car in this instance.

What does it do? This airflow pushing on the rear quarter panel is helping the race car to not pin out. It is like a hand providing a small amount of push on the rear quarter panel, at corner turn in. It was big in NASCAR back when they hand built bodies. They would make & massage the right side of the race car & specifically the rear quarter panel (fender) to catch airflow. They would do the opposite on the left side. See image of Cup car below. These were called "Twisted Sister" cars. Think of it as a small billboard out in the wind. They want it to catch side airflow as the car turns into the corner.



They would finess the door & lower rocker sheetmetal to help increase airflow onto the rear quarter. None of generated a ton of sideforce. But it mattered. If you didn't have it & your competitors did, they were beating you on corner entry & middle. Middle? Yes. Because if we can use 60-100# of sideforce to help the car not be loose on turn-in ... then we can mechanically free up the car to turn better in the middle.



I did the same thing with my NASCAR Modiifeds (see photo above). Al the Modifieds run flat side bodies, so nothing new. We just braced the right rear quarter so it didn't flex & lose the sideforce. We alos added a 4th spill plate runner in the middle of the spoiler. All those things add to help the race car have grip on corner entry. Again, there is a LOT more to learn in the Designing & Tuning Aerodynamics forum thread.

Bonus Tip: Grip Creates Harmonics
Grip creates harmonics. Period. Anytime we create more grip in a race car, we will have more harmonics. Higher spring rates?  More harmonics. Higher sway bar rates?  More harmonics. Stiffer valving to control the springs & bars? More harmonics. Shorter sidewall tires? More harmonics. Wider wheels & more tire pressure? More harmonics. Big aero creating downforce and load on those springs & tires? More harmonics.

Heck, extreme grip can be violent. Seriously. Ever watch a rear tire launch on a top fuel dragster? It is violent. Even in Pro/Stock & Pro/Mod doorslammers with 1000-3000HP, the launch can be violent. So much so it creates violent tire shake. I've personally seen drivers knocked unconscious from extreme tire shake. This is super high harmonics.

We get a high enough harmonics in road racing cars to experience tire chatter. I've seen it ... and felt it ... in front tires & rear tires. Where the tire is gripping ... letting go ... re-gripping ... letting go ... many times in a fraction of a second. That's road racing's version of tire shake. It is from grip harmonics. All grip create harmonics.

Ok. Ok. There are exceptions to the rule. Eliminating chassis bind reduces harmonics. So does eliminating stiction throughout the suspension. But, for the most part, creating race car with a high level of grip, brings a high level of harmonics with it.

This is not comfortable in the car. In fact, it is downright uncomfortable & will wear out the average driver in a shorter time. If the goal is to build a winning race car, the driver & crew need to embrace harmonics as a side effect of going faster. The driver needs to be in better shape & not complain about the harmonics to the crew. Because the only cure is to reduce grip & slow the car down.

Now, if you have a track car, and driving is all about fun, you need to decide what level of harmonics are you willing to live with in the car, to outrun all of your friends. Thank goodness track days only run 5-15 laps, then you get a break. But endurance racers, you need to decide how much grip do I need to win over my competitors, without wearing out the driver(s).

I'll close out this section & open it to questions on creating grip with a 4-page grip summary.