The rear geometry needs to be arranged so that minimal rear steer takes place in order to keep the car going straight ahead, much like an asphalt car. With all four tires on the ground, a high amount of LR weight can be put in the car to provide improved traction off the corners. The car will turn in well and drive through the middle because of the balanced setup causing the LF tire to work to turn the car. Some racers have even been known to run a stiffer RR spring when conditions warrant less RR chassis travel.

Mid-Point Traction
As the track begins to dry out through the qualifying heat races, a team must observe the surface conditions during the heats just before they race. If the track is going black-slick, the setup may need to change as well as the tire selection. These slicker track conditions can cause excess heat buildup in the tires, and more siping is required to help cool the rubber.

The RR can be a little softer to promote traction off the corners, but that will produce more chassis roll at the rear and unload the LF tire. The LF is not going to hike up, but it will become less loaded. So the crossweight, or LR weight, will need to come down so that the balance of weight between the rear tires doesn't become uneven. This prevents a condition in which the LR (as well as the RF) ends up with a high weight while the RR supports very little weight. Less equally loaded rear tires mean less traction off the corners.

Dry, Slick Conditions
As the track dries out further and the surface becomes dry and slick, drastic measures must be taken. We need more weight transfer, a sideways attitude of the car relative to the direction of travel, and a rear geometry that will help overcome the tendency of the car to push on entry and through the middle.

We would soften the right-side springs to help the front turn and the rear to promote traction off the corners. The track bar must be mounted on the left side of the chassis and angled to a greater degree (left side higher) to help pin the RR tire. The greater angle of the bar also causes the chassis to hike up in the rear, which produces rear steer, the degree dependent on the angle of the linkage bars in the rear suspension.

While all of this is happening, we need to make sure that the LF doesn't lift too high off the ground. Recall the aero discussion about keeping the nose close to the ground to keep the downforce in effect. The LF tire can be floating somewhat, but if it is not well off the ground allowing air to get under the front end, the aero will still work.

A considerable amount of rear steer (steering to the right, usually utilizing the LR coming forward) may promote the aero effect, which helps keep the car down on the inside of the track in the corners. This comes from the flat sides of the car striking the air, similar to the effect of a wing on a Sprint Car. Once the car has moved through the middle and it is time to accelerate off the corner, we need the LR to squat and the tire to come back into a more straightforward position for better exit performance.

Most racers now agree that all rear steer should be accomplished through LR wheel movement. If the RR wheel moves excessively, the feel is inconsistent to the driver because the RR is normally the dominant driven wheel off the corners. The movement of the LR wheel is much less offensive in nature.

In a particular event, we may experience a wide variety of track surface conditions that require us to adjust our setup. A team that makes an educated guess about the changes to make has a better chance of winning than a team that makes very few changes. It takes a lot of work to make these changes, and we must think correctly in order to make the best changes.

In the long run, if we expect a fighting chance at winning, we must learn to react. After all, the top teams have definitely learned, they make the adjustments, and, best of all, they win often. Next month we will detail how to make those adjustments.

Billy Moyer Racing Steve Smith Autosports
P.O. Box 11631
Santa Ana
CA  92711
Brian Birkhofer Racing