Mid-Turn Performance
First Always evaluate and correct the mid-turn performance first. Balancing the car at this steady state on the track will also help to balance it on entry and exit. Steady state is defined as a condition in which the car is neither accelerating nor decelerating. The dynamic affects of longitudinal weight transfer from braking or motoring off the corner are not affecting the evaluation at this point in the test.
The balance of the car can be predicted by using computer software beforehand or by using the tire temperatures. The easiest way to make a car handle neutral is to adjust the crossweight percentage. Crossweight is the percentage of the total weight of the car that is supported by the right-front (RF) and left-rear (LR) tires as read on the scales. Lowering the RF and LR corners will reduce the crossweight percentage and loosen the car. Raising the left-front (LF) and right-rear (RR) corners will have the same effect. Change all four corners to effect a change in the crossweight.
After the car is made neutral in handling, make a couple of hard runs and note the tire temperatures. A car that is balanced in terms of the dynamics related to how the front and rear suspensions are working with or against each other will show balance in the tire temperatures. The LF tire will be near the same temperature and working as hard as the LR tire in a balanced setup.
If the LF tire is the coolest tire on the car (by far the most common condition), make changes to the setup to help heat up that tire, making it work harder. Here are a few changes that will give you these results: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.
With each change, you will need to change the crossweight percentage to maintain the neutral handling. The crossweight will have to increase. As the LF tire begins to have more grip and work harder, the car will turn better and it will need to be tightened up using a higher percentage of crossweight.
Ackermann Danger
If your team has always used Ackermann to help the car to turn in conjunction with an unbalanced setup (the LF tire runs cooler than the LR tire), the Ackermann will have to be reduced as you make changes to load the LF tire. A tire that is not working much (less vertical load) will gain traction by using Ackermann. If that tire is loaded, 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 will be trying to go in different directions, and both will give up their grip on the track.
Finding the dynamic balance for the car is not the end goal but the foundation of a good setup. It is the first and most important step in the overall setup for the purpose of getting ready to race. The driver will now feel small changes to the setup. The setup can be further fine-tuned for improved entry and exit performance.
Entry Tuning
Entry problems are almost always caused by rear alignment issues or by incorrect shock rates, mostly in the RF and LR corners of the car. Make sure the rearend is properly aligned and square to the centerline of the car. You could struggle long and hard to overcome a poorly aligned rearend to no avail. No setup change can effectively overcome an alignment problem.
If tuning entry performance with shocks, 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 that results in excess camber change, causing the RF tire to lose grip.