The angle of the rear trailing...
The angle of the rear trailing arms is critical in determining the degree of rear steer your car will have. If the car squats excessively as power is applied, it is possible that the amount of rear steer will increase to make the car too loose or too tight off the corners.
3. Rear Steer - The car could develop a loose condition if the rear suspension is designed to steer to the right as the car squats on exit under full acceleration. The suspension links may produce zero steer under normal cornering attitudes associated with rolling and diving. That may change as the car squats after weight has transferred under acceleration so that the new arm angles now produce rear steer to the right.
Adjust the angles of the rear control arms so that you will have near zero rear steer when the car is at the exit attitude. An increase in the amount of anti-squat also serves to limit the amount of rear suspension movement while the car is accelerating, which reduces the effect of rear steer.
4. Traction Control - If the car is good through the middle and initial exit, but loose off the corner as we get into the gas, then the problem might be that of power-induced wheel spin. In this case, we need to further develop our traction-enhancing program. The primary goal is to eliminate the "shock" that reaches the rear tires due to engine torque that comes from initial application of power. We can utilize systems that increase the crossweight percentage and that also produce rear steer to the left to help tighten a loose-off car.
5. Weight Distribution and Placement - If we feel comfortable with the balance of the car as well as the geometry of the front and rear ends, we might just be setup a little too loose with the crossweight percentage. The car might be able to handle more crossweight and still turn fine through the middle of the corner. A car that is more "free" feels really nice through the middle, turning with almost no effort, but we need a slight amount of "tight" to assist our exit performance.
One driver who had won several championships always drove faster, especially during the race, if the car was a little tight in the middle. He would say after a practice run, "She's pretty good, just a touch tight in the middle." When I would take that "touch" out of the car, he lost 2-3 tenths.
The pull-bar is just one device...
The pull-bar is just one device that racers use to reduce "shocking" the rear tires as the driver gets back into the throttle. The link is spring-loaded and allowed to extend against the pressure of the spring to absorb some of the force of initial acceleration. Other types of devices for this use are lift arms and even leaf springs. The leaf type of suspension has a limited amount of wrap-up from the torque of the engine and acts like a pull-bar to some extent.
A driver must feel that the rear of the car is under him/her so that they feel confident pushing the speeds in the turns and taking the car to the limits when passing other cars or holding off a challenge. That is exactly why we need the front geometry to be correct so that when we need to turn the car against a tighter setup, it goes where we point it.
6. Tight/Loose Syndrome - The limit to what was discussed above is when we set up the car to be too tight. We have learned that a tire will actually gain traction as we increase the angle of attack, or in simpler terms, when we increase steering wheel input. If we have a tight car in the middle of the turns, we can compensate by increasing the steering input and the front will gain traction to match the rear.
The problem with this is what we call the "tight/loose syndrome." When the car is set up too tight, we can still possibly overcome that with even more steering input, but at some point, and this happens very quickly, the balance is reversed and the front ends up with more traction than the rear.
This almost always occurs right around the time of getting back into the throttle. The car is already going loose and then, bam, we gas it and then the car really goes loose. The driver comes in and swears the car is loose, but if we can recognize the tightness in the middle evidenced by the amount of steering input, then we will be able to apply the correct fix-loosen the car for a more balanced mid-turn.
7. Sway Bar Preload - One effect that serves to tighten a car that is loose off the corner is sway bar preload. It has been demonstrated many times that we can help provide more traction off the corners by adding preload to the sway bar. A caution here is in order. If we know the correct crossweight the car needs for mid-turn performance, then we need to arrange weight on the car after we preload the sway bar. Adding preload, especially when using a larger diameter bar, really adds to the crossweight percentage.