Part 4 of 4

How do you increase the TRS number and reduce the car's average roll angle with setup?
• Bigger sway bars ... or stiffer springs ... or some combination of both.
• Remember, the suspension has to travel, so lean towards one of the proven strategies of low travel/high roll or high travel/low roll.

How do you tune the roll angles individually & therefore the diagonal roll angle?
* This is assuming you have achieved the desired target "Average Roll Angle" and just need to balance the car for neutral handling.

If the car is tight/pushy ... decrease the FLLD % (& increase the RLLD%) ... to loosen the car up:
• Decrease front spring rates
• Increase rear spring rates
• Decrease front sway bar rate*
• Increase rear sway bar rate*
• Narrow the front track width
• Widen the rear track width
• Lower the front roll center
• Raise the rear roll center
• Raise the front CG
• Lower the rear CG
• Combination of these tuning items

If the car is free/loose ... then do the opposite of the above to increase the FLLD % & decrease the RLLD% ... to tighten the car up.

These are not the only tuning options to tune the handling of the car on cornering. Far from it. These are the simple items to tune the front to rear percentage of roll resistance in your suspension to balance your car for neutral handling. Shock valving is a fine tuning tool also, but doesn't show up in TRS, FLLD or RLLD calculations.

There are many real world exceptions to the tuning guidelines above. Some of the biggies are:
• Anything that reduces the contact patch or effectiveness of the front tires
• Anything that reduces the working/loading of the inside front tire.
• Anytime you get a tuning setting outside of its happy window.
• In the advanced racing suspensions I deal with, there are also things we do with
extreme shock valving, bump stops, sway bars & roll centers, that the typical formulas
don't take into account.

*Examples of exceptions:
• If you increase the Diagonal Roll ... with the goal of turning better ... and don't adjust & correct the dynamic camber of the front tires to maintain the optimum contact patches, you may not free the car up. In fact, you may make it tighter/pushy midcorner.
• If you decrease the front sway bar rate too far ... in an attempt to achieve more Diagonal Roll onto the outside front tire ... and this change reduces grip of the inside front tire ... it will not turn better. In fact it may push.
• If you go too stiff with the rear sway bar rate ... outside its happy tuning window ... it can keep the inside rear tire "too engaged".
• If you go too stiff with the rear spring rate ... outside its happy tuning window ... it can keep the inside rear tire "too engaged".
• Stiffer rear springs or sway bars need a lower roll center keep the inside rear tire disengaging, to the proper degree, when turning.
• Tuning a race/track car is all about the total combination, not one change.

Rookie tuners often get themselves confused because the change they made ... that the book said will work ... didn't work or even made it worse. They don't understand why it didn't work ... because they didn't think about what else that change affected ... and "the book" didn't cover it. Veterans learn from lots of real world track time, testing and racing. I have seem lots of "experts" with book knowledge think all tuning changes are absolute. Tuners, Crew Chiefs & Race Engineers with real world experience ... who have been there & done that ... and know better

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Amount of front end travel combined with the degree of roll angle:
While the ideal degree of front-to-rear roll angle difference may be similar in the two suspension strategies ... the front & rear roll resistance (FLLD %) required to achieve this angle is not necessarily the same. Conventional low travel/high roll set-ups do not transfer as much load to the front ... so there is less load to control with roll resistance.

Modern high travel/low roll suspensions transfer more load to the front end ... so there is more load to control with roll resistance. There is not a huge difference, but a difference nonetheless.

So, a car with a 53% front weight bias and a FLLD of 58%
• May be on the free/loose side with a modern high travel/low set-up ... and need a FLLD of 58.5-59.5%
• May be on the tight/pushy side with a conventional low travel/high roll set-up ... and need a FLLD of 56.5-57.5%
• This is if all other factors were the same ... and they rarely are from car to car.

FLLD % is a great guideline, but only a guideline. We can not go to ten different cars (all with a 53% front weight) ... and simply say 58% is the optimum FLLD % for every one of those ten cars. There are too many other factors that affect the car's turning ability to say there is an optimum FLLD % that will absolutely work for every car.

Here are examples of other factors:
• If the front steering geometry is not optimum ... and the tires are not achieving optimum contact patch ... the car is going to be tight/pushy.
• If the car has a lot of jacking effect from a high caster & high scrub radius, that car will be looser.
• If the car has little jacking effect from low caster & low scrub radius, that car will be tighter.
• If the car is not aero balanced ... with too little rear downforce ... that car will be looser.
• If the car is not aero balanced ... with too much rear downforce ... that car will be tighter.
• If we run bump stops with super soft springs ... and allow the car to travel past its optimum point ... that car will be loose.
• If we run bump stops and shim them to reduce the travel too much ... that car will tight/pushy.

If you have these issues, you can band-aid the problem with different track widths, spring & sway bar rates to get the car neutral, but it's won't be as fast as the car is truly capable.

Reminder: FLLD % is calculated utilizing the front & rear spring rates, sway bar rates,
track widths, weight bias, CG height & roll center locations.

FLLD % can tell us when we should look at other areas for our handling problems. Using the same example of a car with 53% front weight and a baseline FLLD of 58% ... if we find we need a far different FLLD percentage to get the car to handle neutral ... we probably have problems somewhere other than spring & sway bar rate. Make sense?

If that car is pushing with a 58% FLLD ... and you fix it with a softer front sway bar that gets the FLLD to 52% ... The push is probably being caused by something else, like:
• Less than optimum front geometry & less than optimum contact patch under dynamic
conditions.
• Too little jacking effect.
• Too much rear downforce
• Etc, etc.

I did not go into every possible problem here, but I hope everyone has embraced that FLLD % is a good tool for working out your front & rear spring rates, sway bar rates, track widths, weight bias, CG height & roll center locations for a total handling package.

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Summary:

For Optimum Corner Handling ... You Need to Disengage the Inside Rear Tire ... To a Degree Diagonal Roll is the method to achieve this, utilizing the g-forces of braking & cornering.

The keys to controlling the amount of Diagonal Roll & therefore the degree the
inside rear tire disengages:
• Degree of jacking effect ... from KPI, caster & scrub radius ... and rear spring rate.
• Roll angle difference ... front to rear ... achieved with suspension tuning
• Remember the amount of front end travel combined with the degree of roll angle plays a role.
• Utilize FLLD percentages as a tuning guideline

I want to open up conversation for any questions or thoughts on diagonal roll, jacking effect, TRS, FLLD, etc.[/b]

Part 3 of 4

Diagonal Roll angle can not be measured statically with accuracy. If you put the car on scales & turn the wheels, the weights stay the same as the springs absorb the ride height changes. We have "tricked" the car by putting solid rods in place of the shocks, but all you're learning is the concept. No accurate numbers. We can simulate it on a pull down rig, but it requires the front suspension be on coil bind or bump stops. But to be accurate, you need suspension travel numbers from actual track testing.

You can accurately measure it on track with data acquisition & shock sensors on all four corners. As you increase the caster or scrub radius, the amount the outside front tire compresses ... and the amount he inside rear extends ... increases. Frankly, we don't pursue this line of data. We know the concept exists and accept it as a key element. We don't add caster, or reduce caster, to effect the jacking effect. We tune the caster to achieve optimum contact tire patch. Anything different than that will produce slower lap times because the degree of front tire grip goes down.

We also tune the dynamic toe-out (static toe, toe-out gain from bump steer & ackerman all combined) to optimize the slip angle of the inside front tire ... again to optimize the total grip both front tires have.
If you refer back to my earlier fundamental statements, I mentioned you need to get the inside rear tire to disengage ... to a degree ... to achieve optimum turning. As we have been discussing now ... we achieve that through the Diagonal Roll of the car ... with the inside rear lifting & unloading that tire to a degree ... while compressing the outside front tire & loading it more.

The jacking effect helps us achieve that, but in most production body shaped cars ... with 48-56% or more front weight bias ... we "usually" don't tune this with caster or scrub radius changes. Realize they will affect it, but the cons make this line of tuning less than ideal. So what changes can be made to affect the amount of Diagonal Roll ... and therefore to what degree the inside rear tire is being disengaged during cornering?

Anything that makes the front roll angle less than the rear roll angle. Or, said the other way, anything that makes the rear roll angle more the front roll angle. The key here is compressing the front suspension more, without any additional roll angle in the front. Or, in the rear, increase the extension of the rear suspension ... with a little additional roll angle ... coming from the extension of the inside corner, not from compression of the outside rear corner.

Specifically ...
•    Softer front springs with a bigger sway bar
•    Stiffer rear springs with a smaller (or no) sway bar
•    Lower CG's front & rear
•    Softer compression valving in the front shocks
•    Softer rebound valving in the rear shocks
•    Wider rear track width
•    Combination of these tuning items.

I only laid out tuning options above to "increase" diagonal roll. Obviously, going the opposite direction will decrease diagonal roll. Like anything in tuning, you can have too much or too little. The key is to tune these items to get the inside rear tire to disengage ... just enough ... to make the car turn easily through the corners. Too little ... and the car is tight or pushy. Too much and the car is loose.
Make sense?


Difference in front to rear roll angle:
Track cars NEED to travel the suspension ... to load certain tires more & others less when cornering ... and there are two proven approaches. At the start of this thread, you probably read about the two common suspension strategies. Conventional strategy utilizes stiffer front springs for less front suspension travel under braking & modest sway bars for a higher roll angle. Modern strategy utilizes softer front springs for higher front suspension travel under braking & very large sway bars for a very low roll angle.

Said simply, conventional rolls more & pitches less. Modern rolls less & pitches more. But regardless of the strategy chosen ... the rear roll angle needs to be slightly more the front angle ... to achieve proper Diagonal Roll and disengagement of the inside rear tire.

Here are two real suspension travel examples in similar cars, with numbers rounded off for easier discussion. (I used these same numbers in a previous discussion in a different forum thread.)

Notes:
• These are shock travel numbers, measured in inches, during braking & turning
• The front shocks are 50" apart, which helps us calculate front roll angle
• The rear shocks are 58" apart, which helps us calculate rear roll angle
• + means the shock extended
• - means the shock compressed
• This is a RH corner, for a LH corner, the numbers simply reverse
• These roll angle degrees are "close" but don't account for outside tire squish.

A. Conventional Low Front Travel/High Roll Set-up
LF -1.500" ... RF +1.000" ... Difference 2.500" ... Front Roll Angle 2.86°
LR -1.875" ... RR +1.375" ... Difference 3.000" ... Rear Roll Angle 3.21°
Roll Angle difference: 0.35° (more in rear)
Average roll angle: 3.04°

B. Modern High Front Travel/Low Roll Set-up
LF -3.000" ... RF -2.000" ... Difference 1.000" ... Front Roll Angle 1.15°
LR -0.750" ... RR +0.500" ... Difference 1.250" ... Rear Roll Angle 1.48°
Roll Angle difference: 0.33° (more in rear)
Average roll angle: 1.32°

There is a LOT to learn from these notes about these two different strategies.

The major key differences to note are:
• With the conventional set-up, look at how much more the car rolls, measured in inches.
• On the conventional set-up, notice how both the inside front & rear suspensions "extend" & lift.
• In the modern set-up, see how both sides of the front suspension compress. The inside corner does not lift, it just doesn't compress as far.
• In a modern set-up, only one corner ... the inside rear ... actually extends while
cornering & braking. Everything else compresses.
• On a conventional setup, note how the rear suspension travels slightly more than the
front ... and a lot more than the modern set-up.
• On a modern low roll set-up, note that the front suspension travels significantly more
than the rear suspension.

The similarities are:
• Both set-ups have a higher rear roll angle compared to the front roll angle.
• Both set-ups achieve a similar difference in front to rear roll angles.

Regardless of suspension strategy chosen ... low roll, high roll, tweener ... you need the
rear roll angle slightly greater than the front roll angle.

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Tuning Roll Angle & Diagonal Roll


When designing a suspension or tuning a race car, I utilize calculations known
as:
• Total Roll Stiffness (TRS) measured in pounds per degree of roll angle
• Front Lateral Load Distribution (FLLD) expressed in a percentage of TRS
• Rear Lateral Load Distribution (RLLD) expressed in a percentage of TRS

I know some tuners utilize spring frequency and/or front & rear roll couple numbers. These numbers don't provide us as clear of a picture as TRS, FLLD & RLLD. Total Roll Stiffness (TRS) calculations provide us with an easily quantifiable measurement of roll resistance in the suspension. It takes into account spring rates & sway bar rates.

FLLD/RLLD calculations use this number ... plus front & rear track widths, front to rear weight bias, CG height, front & rear roll center locations ... to provide us the percentage of "Total Roll Stiffness" in the front suspension (FLLD %) and the rear suspension (RLLD %).

Don't get lost in the terms. TRS is simply a way to measure & refer to the stiffness of the spring & sway bar combination. FLLD is simply how much of that stiffness is in the front suspension. RLLD is how much of that stiffness is in the rear.
If we have an example car with springs & sway bars with 3000# of TRS, that means it takes 3000# of force to roll it one degree. If the car also weighed 3000# of total track ready weight it would take approximately 1.0g to roll the car to an average roll angle of 1.0°. By average roll angle, I mean averaging the front & rear roll angles. You still want more roll angle in the rear. In this same example, 1.5g would roll the car to about a 1.5° average roll angle.

If this same 3000# car only had 1500# of TRS
• 1.0g would roll the car to an average roll angle of 2.0°
• 1.5g would roll the car to about a 3.0° average roll angle.

If we had a 6000# truck with 1500# of TRS
• 1.0g would roll the car to an average roll angle of 4.0°
• 1.5g would roll the car to about a 6.0° average roll angle. *Assuming it could achieve
1.5g

Does this help clarify what Total Roll Stiffness (TRS) is?
Now let's move on to splitting this roll stiffness into the front end & rear end. One might incorrectly assume that FLLD 50% & RLLD 50% would mean the car will roll evenly ... front & rear ... on track. This is incorrect because it doesn't take into account front to rear weight bias ... or weight transfer under braking.

Before we go any further, embrace two major things about weight.
1. The end of the car with more weight bias will naturally roll more.
2. Weight transfer to the front, while braking, will make the front roll more when cornering.

So, a car with a 53% front weight bias (and 47% rear weight bias) is going to roll more in the front, unless we stiffen the front suspension to account for the additional weight we have to control. This is accounted for in the formulas. But weight transfer to the front while braking is not. So you need to. I typically target 5% higher FLLD% than front weight bias. With this 5% higher FLLD% ... the car will still achieve a slightly higher rear roll angle ... which is the goal.

If the car truly has a 50/50 weight bias, my target FLLD% would be 55%, and obviously the RLLD percentage would be 45% to make the total add up to 100%. If I have a car with 53% front weight bias, my target FLLD% would be 58%. Simply making the FLLD% higher is not the goal or your desired direction of tuning. This 5% stiffer front suspension, is only a baseline set-up to account for the weight/load transfer from braking hard into the corner. You will need to tune from there.

As a tuning guide only ... because there are exceptions ... TYPICALLY:
a. Decreasing the front roll resistance (FLLD) ... increases the front roll angle ... and loosens the car during corner entry & middle.
b. Increasing the rear roll resistance (RLLD) ... decreases the rear roll angle ... and loosens the car during corner entry & middle.
c. Increasing the front roll resistance (FLLD) ... decreases the front roll angle ... and tightens the car during corner entry & middle.
d. Decreasing the rear roll resistance (RLLD) ... increases the rear roll angle ... and tightens the car during corner entry & middle.

Within reasonable differences making the front track width wider than the rear ... or the
rear wider than the front can be a practical tuning tool. Making the front track width wider than
the rear = tightens the car ... too much makes it push. Wider rear track width than front track
width = frees the car ... too much makes it loose.

What happens if you space the tires in or out ... changing track width ... changes the load distribution on tires. For conversation sake, if we had a car we decided to tune on ... by adjusting track width ... the results would be:
A. Moving the front tires inward, narrowing the front track width, will load the outside front tire more & the inside rear tire less when cornering ... freeing or loosening the car up to a degree.
B. Moving the front tires outward, widening the front track width, will load the outside front tire less & the inside rear tire more when cornering ... tightening the car up to a degree.
C. Moving the rear tires inward, narrowing the rear track width, will load the outside rear tire more & the inside front tire less when cornering ... tightening the car up to a degree.
D. Moving the rear tires outward, widening the rear track width, will load the outside rear tire less & the inside front tire more when cornering ... freeing or loosening the car up to a degree.

Obviously ... how much effect these track width tuning changes make is dependent upon the degree of change. An average sport/club driver would for sure notice a 1/2" spacer reduction or addition. Highly developed drivers that I have worked with could tell if we changed
it 1/16".


*Note: Adding spacers to the front hubs, increases the Scrub Radius. So, when I can use ... either adjustable LCA's ... or simply replace the LCA's for the track width I want ... that is how I prefer to do it, versus adding wheel spacers to the front. I have used wheel spacers in the front many, many times. It's just not my preferred method. Sometimes class rules dictate the decision. Spacers are a no brainer tool for the rear.

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Ideally, you want a wide track width AND zero Scrub Radius. When you're in a situation
where you have to give up one for the other, the rule of thumb is ...

Slower tracks with tighter corners ... give up track width for lower Scrub Radius.
Faster tracks with bigger corners ... accept higher Scrub Radius to achieve wider track width.


Make sense?

Part 2 of 4

Jacking effect:
When the driver brakes & turns the steering wheel (corner entry) ... the outside front tire leans/tilts/cambers (pick a term) back at the top, toward the inside of the corner, as the suspension on that outside front corner compresses. This helps the outside front tire's contact patch optimize on the track surface. This affect also lets the outside front suspension compress a little farther.

At the same time, the inside front tire leans back at the top, toward the inside of the corner. This helps the inside front tire's contact patch be flatter on the track surface. But the inside front suspension does not compress from this action. The g-forces are not going that direction. In fact, this inside front corner lifts somewhat, loading the suspension the opposite corner (outside rear tire). This action, known as the jacking effect, is de-wedging the suspension & creating a rotational axis for the other two suspension corners.

What we end up with is:
• The outside rear tire & inside front tire acting as a rotational axis for the car.
• Diagonal Roll and load transfer from inside rear suspension & tire to the outside front suspension & tire ... "to a degree."
• De-wedged suspension ... "to a degree."

What really happens when we "de-wedge" the suspension with jacking effect in the corner?
• Dynamically ... the spring loads change.
• The inside front corner & outside rear corner see a dynamic spring force increase, helping to load these tires more.
• If the car was flat on all four tires ... which it is not ... the outside front tire and inside rear tire would see a dynamic spring force decrease.
• But because the g-forces are diagonally rolling the car off the inside rear suspension & tire ... and onto the outside front suspension & tire ... the outside front suspension & tire are loaded more than any corner (so lots of spring force) ... and the inside rear suspension becomes "relaxed" and extended, reducing the spring force & load on that tire.

This jacking effect & de-wedging is a critical process that happens in all race cars when turning. You need this jacking effect to disengage the inside rear tire ... to a degree ... and increase load on the outside front tire ... to assist the car to turn. This de-wedging process is key to any & every track car turning well. If you have too much jacking effect ... the inside rear tire gets disengaged too much ... and the car gets loose in the first 1/3 of the corner. If you have too little jacking effect ... the inside rear tire
does not disengage enough ... and the car pushes in the middle of the corner.

What influences the amount or degree of jacking effect?
The two corners of the suspension that form the rotational axis affect it: The inside front & the outside rear. Most tuners only think about the inside front suspension & tire. The degree of caster & spindle KPI affect the jacking equation. But the KPI & caster only control the dynamic camber angle of the tire & wheel when turned. The scrub radius acts as an amplifier. Caster & KPI have a smaller effect. Scrub radius has a bigger effect. The bigger the scrub radius, the farther the tire & wheel are "out" from the spindle pivot axis ... and the more jacking & lifting occurs at the inside front tire, therefore increasing the dewedging effect and increasing the amount of Diagonal Roll travel.

In the simplest of terms ... more scrub radius disengages the inside rear tire ... to a higher degree. While less scrub radius disengages the inside rear tire ... to a lower degree. Tighter corners need MORE JACKING EFFECT. AutoX needs more jacking effect. Super high speed corners need less jacking effect.

The outside rear suspension plays an often forgotten roll. If the outside rear suspension is too soft ... then it simply compresses more as the inside front tire creates the jacking affect. It absorbs the jacking effect. Realize to have a rotational axis for jacking effect ... the inside front & outside rear need to act as a pivot for the other two corners.

• If the outside rear suspension is softer ... the jacking effect is reduced.
• If the outside rear suspension is stiffer ... the jacking effect is increased.

The combination of rear weight bias, springs, sway bar, roll center, track width & CG ... need to allow just enough rear roll angle to disengage the inside rear tire to a degree ... but high enough to prevent the outside rear suspension from compressing so much that the car loses jacking effect. If the rear is too soft, the car will have insufficient jacking effect, insufficient Diagonal Roll resulting in a tight handling condition. If the rear suspension is way too soft ... the car will actually roll diagonally more onto the
outside rear suspension ... and unload the inside front tire ... resulting in a tight or push condition.

It is the combination of the factors starting the jacking effect (KPI, caster & scrub radius) ... and the factors that influence rear suspension compression (spring, sway bar, RC, CG, track width & weight bias) ... together that ultimately determines how much jacking effect we have. If you have moderate to high scrub radius, you will unfortunately need to run less caster. If you have smaller scrub radius, not only can you run more caster, but you NEED to run more caster, to help the car turn.

Everything is a compromise, but you can achieve the optimum jacking effect with:
• Low caster ... by running a higher scrub radius
• High caster ... by running a lower scrub radius
• Low scrub radius ... by running higher caster
• High scrub radius ... by running lower caster

OK, now what?
• First, don't use KPI, caster & scrub radius as independent jacking effect tuning tools. They affect the tire contact patch.
• Don't simply increase jacking effect, without taking into account how the KPI, caster & scrub radius changes affect everything else.
• Do understand & embrace the jacking effect/de-wedging concept as a part of your total Diagonal Roll tuning approach.
• I recommend you set your KPI, caster & scrub radius for optimum tire contact patch.
• Then achieve the rest of your Diagonal Roll travel with front to rear roll angle difference.
• If you need to increase jacking effect, consider stiffening the rear spring rate.

The optimum set-up that performs best ... is zero scrub radius (dynamically) and high caster ...
typically more caster than the spindle KPI. It is optimum, not because it achieves more jacking effect. It is optimum because the "zero scrub radius" produces the least amount of tire tread squirm & scrub when turned ... and the higher degree of caster is utilized to achieve the optimum contact patch & moderate jacking effect.

This conversation is to help us tune the race car for handling balance. So, to be complete...

Let's talk corner exit ...
As you unwind the steering wheel on corner exit ... you are adding "wedge" back into the suspension to help grip the car for faster acceleration. Frankly, this is one part of why running a late apex line is often quicker in tight, low speed corners. It allows you to get the steering unwound quicker ... which adds more rear tire grip for corner exit.

Two key pieces of information:
1. The more compression travel your front suspension has on corner entry ... the more extension travel your front suspension will have on corner exit ... achieving higher levels of rear tire grip ... for a longer distance ... improving your corner exit acceleration.
2. The more jacking effect your front suspension has on corner entry to de-wedge the car ... the more effect the un-jacking effect has on corner exit ... adding back in a higher degree of wedge as you unwind the steering on corner exit ... achieving higher levels of rear tire grip ... improving your corner exit acceleration.

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Just FYI: The term "jacking" is also used in racing to describe:
The effect the control arms have on jacking the frame down and compressing the spring through additional leverage with high upper control arm angles. The effect shocks having in jacking the car down in ride height ... front, rear, or both ... when they have very soft compression valving & extreme rebound valving at 0" inches per second?

The next discussion is broken into 4 parts. This is part 1 of 4.

Diagonal Roll Travel Discussion & Explanation

From the master list above is the definition of Diagonal Roll. [/b]It is the combination of chassis pitch & chassis 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.

Diagonal Roll is normal physics with the braking & turning forces we're introducing to the car. Too much Diagonal Roll is bad ... causing a free or loose condition. Too little Diagonal Roll is bad ... causing a tight or push condition. Our job is managing the amount of Diagonal Roll to achieve neutral, balanced, handling, void of those negative conditions. When the Race Drivers says the car is very "drivable" ... I take that to mean they're not fighting the handling gremlins of loose or push.

To achieve the optimum Diagonal Roll for our desired neutral, balanced, handling, you need to get the inside rear tire to disengage ... to a degree. Restated from above ...

If we have too much Diagonal Roll, we're disengaging the inside rear tire TOO MUCH ... creating a free or loose condition. If we don't have enough Diagonal Roll, we're not disengaging the inside rear tire enough ... creating a tight or push condition.

The best, most confident chassis tuners embrace that ... at the track ... we're simply tuning the disengagement & reengagement of the inside rear tire to achieve handling balance. We are "managing" the Diagonal Roll. Understanding this & mastering this are the most important tuning things you need to know. It is so important, I restate or repeat certain concepts throughout this discussion. It is that important.

Let's take these areas one at a time, starting with ...

For Optimum Corner Handling ... You Need to Disengage the Inside Rear Tire
... To a Degree
"Disengage ... to a degree" means we are reducing the load on that inside rear tire. We may ... or may not ... need to reduce the tire's contact patch. But for optimum cornering ability, we need to reduce the grip of the inside rear tire. This is critical to a good handling car on grippy tires & tight corners.

"To a degree" means we are not lifting the tire off the ground completely. We may not even be close. It simply means we are reducing the load & potentially the contact patch on that inside rear tire. "To a degree" also implies ... correctly ... that we want to control how much. This is key. If we do not disengage the inside rear tire enough, we struggle with a tight/pushy car. If we disengage the inside rear tire too much, we now have a loose car to deal with. How much is right? The answer depends on many factors and varies by track, car, set-up & driver. Heck, it will vary throughout the day as track
conditions change.

"Re-engage" means we want to "plant" the inside rear tire hard on corner exit ... to regain & achieve a loaded, full contact patch ... so we have two full tire's worth of contact patch for accelerating. This happens as the driver unwinds the steering wheel. "How much" is determined by suspension geometry, shocks, springs, etc.

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How do we disengage the rear tire to a degree? ... by managing the AMOUNT of Diagonal Roll travel.
Again, Diagonal Roll travel is the combination of roll & pitch. Pitch happens under braking. How much body/chassis pitch we have (typically measured in inches) ... is created by braking g-forces & can be managed with CG height, ride heights, weight bias, spring rates, shock valving, bump stops, anti-dive & aero, as well as the Race Driver's degree of braking.

Roll happens during cornering. How much body/chassis roll we have (typically measured in degrees) is created by cornering g-forces & can be managed with CG height, ride heights, weight bias, spring rates, shock valving, bump stops, sway bar rates, roll centers & track widths, as well as the Race Driver's cornering speed.

Diagonal Roll travel happens during the combination of braking & cornering. Diagonal Roll travel is when the inside rear suspension extends, unloading the inside rear tire "to a degree" ... while compressing the outside front tire farther & loading it more.

Think about the car dynamically on track. When you come up to a corner, you brake first, and the front suspension compresses evenly. A lot of weight has transferred from rear to front. The rear tires have less load & less grip. The front tires have more load & more grip. Now ... you turn into the corner. This doesn't happen "all at once" ... it happens gradually. Let's say it's a right hand corner. When you first move the steering wheel to the right ... weight starts to shift to the left side tires.

Because you're still on the brakes while turning ... the left front tire is now getting more load than any other tire ... and the loading will increase as you turn the steering wheel more and the car turns harder into this right hand corner. If you're running a modern low roll set-up, the inside front tire is still an effective & vital part of the front suspension & grip equation. It's just not doing as much work, or providing as much grip, as the outside front tire.

Make sense so far? If not, please ask questions.

For optimum cornering ability, you need Diagonal Roll to disengage the inside rear tire "to a degree" and load the outside front tire more. The "to a degree" part is critical. As mentioned above, if you disengage the inside rear tire too much, the car is loose on corner entry & middle. If you don't disengage the inside rear tire "enough" the car is tight/pushy in the middle of the corner. (Entry also ... if extreme.)
Tip: You don't "make" Diagonal Roll happen. The natural g-forces caused by braking & turning make the car want to diagonally roll. You simply need to control "how much" with suspension tuning.

The keys to controlling the amount of Diagonal Roll & therefore the degree the inside rear tire disengages:
• Degree of jacking effect
• Difference in front to rear roll angle
• Amount of front end travel combined with the degree of roll angle

Let's take them one at a time

Where do I start tuning?

Separate tuning mechanical grip versus aero grip. First, we need to be clear on the difference. Mechanical grip is tire grip created by the chassis, geometry, suspension & steering... with no aerodynamic aids to create grip through downforce.

The chassis part is weight, distribution, center of gravity, track width, etc. The suspension part is springs, sway bars, shocks, control arms, stiction, etc. The geometry includes dynamic front & rear roll centers, camber & caster gain, anti-dive, anti-squat, etc. The steering part includes toe settings, bump steer, Ackerman, steering input, etc. All of these components contribute to the raw handling of the race car & the net result we call mechanical grip.

Aero grip, is additional grip we create by adding aerodynamic aids to create downforce on the car & therefore on the tires. Wings, spoilers, air dams, splitters, diffusers, smooth belly pans, canards, etc. all combine to create downforce in some quantifiable amounts, front, rear & total.

Which do we tune first?  This answer should make it clear. Think of the grip in layers. The mechanical grip is the bottom layer & the aero is the top layer. In running your race car, you ALWAYS have the mechanical grip, but you don't always (at lower speeds) have aero grip. So mechanical grip is your FOUNDATION. Aero grip adds a LAYER of GRIP on top of the mechanical grip in the higher speed corners, where you need it, to create more TOTAL GRIP.

Design your car's front aerodynamic aids to create maximum downforce in the front & leave it alone. We don't "tune" to reduce the front downforce in full bodied, front engine cars. We want all we can get up front. Then we balance the aero at the rear of the car. Design & adjust your car's rear aerodynamic aids to create a measure more downforce than you'll ever need.

While driving & tuning for the slower corners of the course, we don't want to crash the car in the faster corners. So, to be safe, we always adjust the rear aero in the shop for more rear downforce than we need. This way, if we start to over drive the fast corners, the car will push & let us know to back off, instead of the rear end stepping out at high speed & ruining our day.

Plan your tuning sessions this way. Start in the slower corners, 40-70 mph, to dial in the suspension to make the race car handle optimum here. We need the mechanical grip ... front & rear ... to be both maximized & balanced ... to be fastest in these slower corners. Ignore total lap times. Utilizing segment timers, as well as driver feedback, is the best method here.

Then we move on to trimming out the rear aero to achieve the most BALANCED total grip we can get in the fastest corners. "Trimming out" means to take out rear downforce a step at a time. All wise racers & teams that run aero, set the rear aero to create a slight "aero push" in the high speed turns. Then they trim it out a step at a time. This is the safe way.

Starting with the car "aero loose" is fu@#ing dumb & a great way to crash the car. When testing a brand new car, always start with max rear downforce & trim it out when tuning.

Lastly, and this is KEY, aero downforce is not an absolute. Airflow is a variable. If we have a headwind, we'll have more downforce. Tail wind? Less downforce. Crosswind? Who knows!  Hang on!  A wheel jerking Driver can make downforce disappear long enough to crash. With significant aero, the Driver HAS TO BE SMOOTH as glass ... or bad stuff will happen.

To start, I recopied these handling conditions & their definitions, from the master list above.

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.

Let's define "Overall Handling Balance." "Balance," "Good Grip" or "Neutral Handling" all are terms that mean both the front & rear tires have good traction, neither end is over powering the other & the car is turning well. Both the car & driver are happy.

What we not going to cover here in this thread is how to increase overall grip. That is a different forum thread. Nor are we discussing how to increase grip on one end of the car. We are talking about managing the grip the car has on all 4 tires, to make it brake, turn & accelerate well. Or at least to the best the compromise of those 3 are possible.

We will be talking about shifting grip fore & aft ... from front to rear, & rear to front ... to achieve handling balance. We will also be talking about shifting grip diagonally from corner to corner, to achieve handling balance. In most cases, the tuning changes we make do not increase or decrease total grip. We are just shifting it around. There are a few exceptions, where tuning changes actually decrease grip on one end of the car or one corner of the car. And while this may achieve handling balance, it is not good. We don't want to tune ourselves to less total grip. I will outline the items that can do that, so as to avoid them.

Before we get into handling problems & solutions
... I want to share with everyone a viewpoint to make tuning easier ... then outline terms & critical tuning concepts ... so we're on the same page.

Competition cars are COMPLEX. There are literally over 200 AREAS of things to TUNE in the suspension alone. What helps a Tuner/Crew Chief to become more confident is ... knowledge (of course) ... experience (of course) ... knowing what a mechanical change actually effects on track ... and how each tuning change of affects other areas.

But also, as a Tuner/Crew Chief, having a viewpoint that makes all this complexity ...
simpler to understand ... provides clarity & builds confidence.
I have developed many crew chiefs over the years to work with me on my race teams. Teaching them everything they need to master is a long term commitment on my part & theirs. It takes years. But simplifying things help them grasp concepts quicker ... and develops confidence in their tuning decisions.

Let's simplify things first. Remember this little corny phrase: 4x4x2+2
It is short (like an acronym, but using numbers) for ALL the things that competition car Designers, Tuners & Crew Chiefs deal with. There are 4 key areas with 4 major ingredients, operating in 2 worlds ... plus 2 wild cards. 4x4x2+2 is just a simple way to remind us what we're dealing with.

The 4 key areas are: power, braking, handling & aerodynamics (in no particular order.) Obviously these all play a role in the performance of the car ... and in many cases affect each other.

Each Key area has 4 major ingredients that define it & of course affect it.


For power, the 4 major ingredients are:
Airflow
Fuel management
Spark control
Structure Design

For braking, the 4 major ingredients are:
Hydraulics
Leverage
CoF
Structure Design

For handling, the 4 major ingredients are:
Tires
Weight transfer ... to and from tires
Geometry affecting ... the tires
Structure Design

For aerodynamics, the 4 major ingredients are:
Force
Drag
Turbulence
Structure Design


When I said competition cars operate in two worlds, what I really mean is we do a lot of design, set up & tuning to the car in a "static state" ... then go drive it HARD ... and everything is affected & different when the car is in a "dynamic state" on track.
No pun intended, but the 2 wild cards are the track & the driver. The track environment is constantly changing, and good Tuners/Crew Chiefs tune to the changing conditions.

As long as we use human drivers, this will be a variable. Some drivers are more consistent & some less, but none of them are robots, so there will be inconsistencies. Some drivers are learning & improving, some not & even some declining in their abilities, but again, they are not static. Some drivers are more of a wild card than others.

As long as we simply embrace these 4 key areas, understand the 4 major ingredients that define & affect them, remember the car is acting in a dynamic state on track & account for the 2 wild cards ... the job of Tuner/Crew Chief gets more clear, less daunting and making tuning decisions becomes easier, quicker & more confidently.[/b][/color]

Is anyone running a residual valve on their brake systems? I'm having some pedal bleed down. Have to pump pedal after a bit. Thinking I might need a residual valves.  7/8 Willwood master cylinder was stoptech brakes.

Quote from: Ron Sutton on Apr 12, 2026, 01:46 PMI am a fan of the both the Fuel Lab brand & Radium Engineering brand of Top Plate systems with Fuel Cell Surge Tanks.  They only cost a little bit more money than running the square collector in the bottom of the tank.  They pickup more fuel, increasing how far we can run on the same number of gallons.

FuelSafe told me the Radium Engineering brand is hard to get sometimes. So they use the Fuel Lab brand more.

Deatschwerks also did their own version with a fabricated aluminum surge tank that serves as a top hat for the cell as well, so there's definitely options for keep it all contained in the cell. External surge tanks are also an option.

I helped a friend make an external version for his car since he was having starvation issues. It incorporated a box style in the cell to an external surge tank the fed the primary pump. The fuel return from the rail ran to the surge tank and then the surge tank had an overflow back to the cell into the box style internal surge tank. Extra component or two, but he really liked his hat and primary pump setup and didn't want to change it. We were able to make the external surge tank to a size and shape that worked best for the space available. Worked great! Solved the starvation issue. Didn't do anything more for using every drop of fuel in the cell, but doing time trials with short sessions on track, it wasn't an issue.

Quote from: Ron Sutton on Apr 12, 2026, 01:34 PMThat seat is awesome. One thing Oval track racers do better is prepare to protect them selves WHEN they crash. Too many "Track Car" guys think it won't happen to them, because they're not planning to push the car 102%. Which is rubbish. A crash at 100mph is a a 100mph crash, regardless of intentions.

I caught myself saying something like this. Had to give myself a little pep talk about it basically as soon as I said it. Noone ever "plans" on crashing. It always happens fast and you have no control over it, hence, "lost control". Someone told me to buy the best safety equipment you can afford, and I've tried to make sure I do that.

A carbon HANS would be nice, but a fiberglass HANS will still save your life - you need one even if its not the best of the best. Make sure and install harnesses correctly. Fire suits are expensive anyway you buy them, so buy the best one you can. Fire extinguisher is better than no fire extinguisher, but you can't really use a handheld extinguisher effectively between the moment you realize you're on fire and the moment you're able to do something about it. I'll do a post on my fire system and harnesses. I think I did them as well as I could have, but its a good topic for discussion.

Quote from: Ryan Kennedy on Apr 06, 2026, 01:28 PMFuel system!

So a note on functionality between the two systems. I didn't have a lot of drive time on the ATL surge tank setup, but it functioned well for the time I did have on it. However...I used the fuel pump in the ATL surge tank to empty the cell before converting to the Radium setup. This left about a half inch of fuel in the bottom of the cell. Once the new setup was completed (minus the shield), the Radium setup was able to fill its surge tank, which is about 2-liters, and prime all the way to the rails with 45psi on the pressure sensor. All accomplished with the fuel leftover that the ATL setup wasn't able to pick up and pump out of the cell. Food for thought.

I have recently added a second hellcat pump into the Radium surge tank to convert to E85, and it was a cinch. The system is already set up for up the 3 pumps and its easy accessing the additional circuits to add pumps. The new Radium FCST's are even easier, making the pump module come out separate form the cell hat itself. Only switching to E85 in effort to bring the operating cost down. I added a Flex Feul sensor so I can run pump E85. Despite the higher consumption, my fuel costs will be cut roughly in half over the 50/50 leaded race gas/non-ethanol pump gas mix I was previously running. Yes, there are extra steps with E85, but as always - I have more time than money. Pumping the fuel system out to save $250/day running the car? Worthit.

I am a fan of the both the Fuel Lab brand & Radium Engineering brand of Top Plate systems with Fuel Cell Surge Tanks.  They only cost a little bit more money than running the square collector in the bottom of the tank.  They pickup more fuel, increasing how far we can run on the same number of gallons.

FuelSafe told me the Radium Engineering brand is hard to get sometimes. So they use the Fuel Lab brand more.