Excess LR shock rebound may cause the car to be loose on entry as the weight is transferring to the front while braking. This LR shock should allow the LR tire to move in rebound to help it maintain contact with the racing surface during braking.
Spring split has an effect on entry performance. 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 like the rearend is not under the car and prevent the driver from going deep enough into the corner. Remember, spring changes also affect the dynamic balance of the car. You will need to re-evaluate the tire temperatures and make changes to the Panhard bar to re-balance the setup after a spring change.
Exit Tuning
Problems associated with corner exit involve either a tight-off or loose-off condition. If methods to gain bite off the corner are introduced, you might end up with a car that does not turn. The changes to improve exit performance must not affect mid-turn balance. So changes to spring rates, spring split, Panhard bar height, and crossweight will all affect and probably ruin mid-turn balance. So how do you tune exit performance?
The tracks where there are exit issues are mostly the flatter tracks with related 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. The amount of grip the rear tires have available on exit off the corners needs to be increased and not affect the mid-turn balance already established.
Experiments can be done with various designs of pull bars, pushrods, lift arms, and associated rear steer that occurs only on acceleration. The goal is to reduce the shock to the rear tires upon initial application of power while increasing total grip by introducing rear steer to the rearend (to the left). The more the rear tires are steered, the more traction they will have.
Always save your sticker tires for the last runs of the day. If the setup is good, make a qualifying run on fresh tires. After that run, do a 25- or 30-lap run on the 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 at the shop and learn from both the gains and losses. All of the results are valuable. The more you learn about the effects of changes, the better quick adjustments can be made during a racing event. The top teams make a point of knowing how each chassis adjustment affects all other parameters involved with their setups.