Track Testing - How To Go Testing

Here are a few changes that help us move toward a more balanced state.

To reduce the tendency for the rear to outroll the front:

1. Increase the RR spring rate or reduce the rear spring split if the RR is softer.
2. Raise the Panhard bar.
3. Soften the RF spring rate (only on lower-banked tracks).
4. Stiffen the LF spring rate.
5. Move the moment center to the left.

To reduce the tendency for the front to outroll the rear (as is often the case when teams try the BBSS setups):

1. Reduce the RR spring rate.
2. Raise the LR spring rate.
3. Lower the rear moment center or Panhard/J-bar.
4. Reduce the size of the front sway bar (2.000-inch diameter might be a bit much-try a 1.750-, 1.500-, or 1.375-inch diameter bar).
5. Stiffen the front spring rates.

The crossweight should be adjusted with each change in order to maintain the neutral handling. The crossweight has to increase in the first examples because the car turns better as the LF tire begins to have more grip and work harder. We need to tighten it using a higher percentage of crossweight.

In the second set of examples, where the front outrolls the rear, the crossweight needs to be reduced as the rear tires develop more grip.

If Ackermann has always been used by the team to help the car turn in conjunction with a tight and unbalanced setup (the LF tire runs cooler than the LR tire), then the Ackermann has to be reduced and/or eliminated as changes are made to load the LF tire. A tire that is not working much (less vertical load on it) gains traction by using Ackermann. If we load that tire, it will really take off in the steered direction and work against the RF tire. The end result will be a severe push as the two front tires try to go in different directions, ultimately giving up their grip on the track.

Finding the dynamic balance for the car is not the end of our goal. Rather, it is the very foundation of a good setup. It is the first and most important step in getting ready to race. Small changes to the setup can be felt by the driver as never before, and the setup can be further fine-tuned for improved entry and exit performance.

Entry problems are almost always caused by rear alignment issues or incorrect shock rates (mostly in the RF and LR corners of the car). The rear end must be aligned properly and square to the centerline of the car. Failure to do so results in a long and hard struggle to overcome a poorly aligned rear end ultimately to no avail. No setup change can effectively overcome an alignment problem.

If we decide to tune entry performance with shocks, we will work with compression rates in the RF and rebound rates in the LR. A RF shock that is too stiff on compression might cause a push on entry. If the RF shock is far too soft on compression, it may also develop a push due to sudden and excessive suspension movement. The result is excess camber change that causes the RF tire to lose grip.

Excess LR shock rebound may cause the car to be loose on entry as the weight is transferred to the front while braking. The LR shock should allow the LR tire to move in rebound to help it maintain contact with the racing surface as the car pitches forward and to the right on entry.

Spring split has an effect on entry performance, too. At flatter tracks, a stiffer LF spring over the RF spring helps entry stability in most cases. To the driver, a stiffer RR spring over the LR spring might feel like the rear end is not under the car and may prevent him or her from going into the corner deep enough on the banked tracks. Spring changes also affect the dynamic balance of the car, and we need to re-evaluate the tire temperatures and make changes to the Panhard bar to rebalance the setup after a spring change.

Problems associated with corner exit involve either a tight-off or loose-off condition. If we introduce methods to gain bite off the corner, we might end up with a car that does not turn. The changes we make to improve exit performance should not change the midturn balance. Changes to spring rates, spring split, Panhard bar height, and crossweight will affect and probably ruin midturn balance. So, how do we tune exit performance?

The tracks where we usually see exit issues are mostly the flatter tracks with associated lack of grip. The combination of lateral forces that come from turning the car and the torque associated with power application tend to overload the grip capability of the rear tires. So we need to develop ways to increase the amount of grip the rear tires have available on exit off the corners while not affecting the established midturn balance.

We can experiment with various designs of pull bars, pushrods, lift arms, and associated rear steer that happens only on acceleration. The goal is to reduce the shock to the rear tires upon initial application of power and increase the total rear grip level by introducing rear steer (to the left) to the rear geometry. The more the rear tires are steered, the more traction they will have, just as we have learned about the front tires associated with steering input.

There is a limit to how much rear steer we can use before the car becomes too tight on exit. Larger amounts are more tolerable on dirt than on asphalt. A few ten-thousandths of an inch of wheel movement fore and aft can be felt by the driver on asphalt, whereas an inch or more of wheel movement is not unheard of on dirt.

Sticker tires should be saved for the last runs of the day after the car is dialed in. If the setup is good, we can make a qualifying run on fresh tires. After that run, a 25- or 30-lap run is made using the newer tires to see if the lap times stay consistent. A truly balanced setup will provide lap times that fall off less than the competition's as more laps are run on a single set of tires.

Back at the shop, we review our notes and learn from the gains and losses. All of the results are valuable. The more we learn about the effects of changes, the better we become at making quick adjustments during a racing event. The top teams make a point of knowing how each chassis adjustment affects all of the other parameters involved with their setups.

Incorrect tire stagger, bent shocks, and suspension binding are some of the peculiarities that can ruin a test session. If radical setup changes do not seem to affect the expected result, then a mechanical problem must be sought and fixed. Stagger almost always closes; it doesn't open. Given the choice, we should use a slightly larger stagger than what we may need.

Test notes should be kept available for review. Testing should take place as often as we can afford and whenever the track is available. If goals are set, performance will improve and racing will be that much more enjoyable. Let us know how you do by sending an e-mail to bob.bolles@primedia.com. We promise not to share your secrets. Good luck.