If tuning entry performance with shocks, work with compression rates in the RF and rebound rates in the LR. A RF shock that's 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 that results in excess camber change causing the RF tire to lose grip.

Excess LR shock rebound may cause the car to be loose on entry as the weight is transferring 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. A stiffer RR spring over the LR spring might feel to the driver like the rearend isn't under the car and prevent him/her from going into the corner deep enough on the banked tracks. Remember that spring changes also affect the dynamic balance of the car and you'll need to re-evaluate the tire temperatures and make changes to the Panhard bar to rebalance the setup after a spring change.

Exit Tuning
Our 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 then end up with a car that doesn't turn well. The changes we make to improve exit performance shouldn't change the mid-turn balance. So, changes to spring rates, spring split, Panhard bar height, and crossweight will all affect and probably ruin our mid-turn 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 mid-turn balance we have established.

We can experiment with various designs of pull bars, push rods, lift arms, and associated rear steer that happen 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 like we've learned about the front tires associated with steering input.

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

At The End of The Test
Always save your sticker tires for the last runs of the day after the car is all dialed in. If the setup is good, make a qualifying run on fresh tires. After that run, do a 30- or 40-lap run on those newer tires and see if the lap times stay consistent. A truly balanced setup will provide lap times that fall off less than your competition as more and more laps are run on a single set of tires.

Review your notes when you get back to the shop and learn from both the gains and losses. All of the results are valuable and the more we learn about the effects of changes, the better we can make 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, suspension binding, and poor alignment are some of the peculiarities that can ruin a test session. If radical setup changes don't seem to affect the expected result, look for a mechanical problem and fix it. Keep your test notes available for review. Test as often as you can afford and whenever the track is available. If you can plan out your goals, your performance will get better and you'll then enjoy your racing experience that much more. Good luck.

Earls Performance
Firestorm Graphix
Five Star
North Minneapolis
Steve Leavitt Racing