If the rear end is positioned...
If the rear end is positioned so that it is aimed to the right of the centerline of the car, the rear tires will continually want to roll outside the front tires. This is obviously going to make the car very loose in all three of the turn phases. It is very important to align the rear end to point straight ahead and also to line up the right side tire contact patches.
A balanced car is evidenced by matching the tire temperatures. The front and rear averages should be close to the same (adding the front two tires and comparing to the rear two tires), as well as each of the side tires should be nearly the same temperature from front to rear. For example: LF + RF = LR + RR, LF = LR and RF = RR. Work to get these temperatures correct and then fine-tune with the crossweight percent.
A Loose Setup
A loose condition at the mid-turn phase is where the car turns well but the rear end is not gripping as well as the front. The feel of the car as well as the tire temperatures can tell a lot about what is causing the loose condition.
A loose car will usually have a right rear tire temperature that is hotter than the other three tires. A loose car will not have enough traction off the corners and will spin the rear tires, especially the right rear tire. Here are several probable causes for a loose car:
1. Rear Alignment
The rear control arms are...
The rear control arms are positioned so that as the chassis moves vertically in the turns, the right rear wheel is moved back, causing a significant amount of rear steer to the right, making the car loose.
The very first consideration is rear alignment. If the rear end is out of alignment with the right rear wheel farther back than the left rear wheel, the car will be loose at all three segments of the turns. This should have been checked in the shop long before the car rolled off the trailer.
2. High Rear Roll Center
The Panhard bar, or whatever represents the rear roll center, may be too high for the rest of the setup. If you have a J-bar setup or a Panhard bar, lower it to tighten the car.
The rear springs may be too stiff, resulting in the front wanting to roll more than the rear. While this is not a common occurrence, it is possible. Soften the rates of the rear springs. Soften only the right rear spring if running on a flat track. This has a large effect, so be careful. The car can change to being tight in a hurry.
If you are able to setup the car so that it is good through the middle of the corner, then we need to work on entry performance next.
A useful design tool is anti-dive...
A useful design tool is anti-dive (A-D), which keeps the front suspension from moving too quickly and too far. It only works while we are braking and that is exactly when we need it to work. A-D is accomplished by angling the control arms from a side view so that as the spindle tries to rotate under heavy braking, the motion of the ball joints is in the reverse direction and resists dive.
A car that is loose into the corner may have any one of, or a combination of, several problems. Let's look at the most common causes of a stock car being loose on entry.
1. Rear Alignment
A rear end that is out of alignment can cause a car to be very loose, especially on entry to the corner. If the rear end is set so that it points to the right of the centerline of the car, then the car will probably be loose into the corner as well as through the middle and off the corner. Nine times out of ten, a car that is loose into the corner has a rear alignment problem that needs to be addressed right away.
2. Improper Shock Rates
The left rear shock may be too stiff in rebound or the right front shock may be too soft in compression which lifts weight off of the left rear wheel on initial entry under hard braking. To fix this, reduce the rebound in the left rear shock and/or stiffen the compression on the right front shock.
3. Brake Bias Imbalance
Make sure your brake bias is tuned correctly. If too much of the bias is on the rear brakes, the car will be more loose under heavy braking than if you lightly brake into the corner. Install brake bias gauges and know the amount of pressure at each set of brakes. Usually a 60 percent front and 40 percent rear bias works for most tracks.