We can use the engine torque...
We can use the engine torque to our advantage by mounting the rear control arms in a certain way. As the driveshaft rotates, the pinion gear (attached to the driveshaft through the Universal joints) engages the ring gear (attached to the axles through the differential) and tries to climb it. This applies a force that will try to rotate the rearend in a counter-clockwise direction when viewed from the right side. If the upper link, on a three link rear suspension, is angled with the front end lower than the rearend, the force that tries to rotate the rearend will try to make the third link more horizontal. This applies an upward vertical force to the front of the link when accelerating that tries to lift the rear of the car. When decelerating, the opposite occurs and the braking forces try to lift the rearend causing the car to be loose. Antisquat should be used in limited amounts.
To a lesser extent, splitting the rear shocks' compression rates will accomplish a similar effect while the shocks are in motion and adjusting to the transfer of weight upon initial acceleration. This effect is very short lived, but can help to compensate for the shock to the tires that comes from the initial application of power. We would increase the compression rate in the LR shock and lessen the compression rate of the RR shock to accomplish this effect.
Sticker "Shock"
We have learned that traction can be better maintained if we can decrease the amount of torque that reaches the rear tire contact patches that comes from the initial application of power. Doing this helps the tires adjust to the transition of forces from lateral to longitudinal.
When we're at mid-turn, the lateral forces will be resisted by the tires at the contact patch and all four tire contact patches will be at the limit of lateral adhesion if we're going as fast as we can go without sliding. In more simple terms, the tires at that point are about to give up and slide. If we can reduce the initial shock that is transferred to the rear tires through the driveline at that same time, we can help the rear tires maintain their attachment to the racing surface.
We do this using devices such as a pullbar or a lift arm. These items momentarily transfer the torque to themselves instantly and effectively at the very moment the throttle is applied.
Traction Circles
The Traction Circle theory of tire technology tells us that there is only so much traction available from a particular tire and its contact patch, no matter what direction the forces are directed. The actual number in pounds of resistance is based on the size of the tire contact patch, the adhesion properties of the compound itself as well as that of the track surface, the amount of load on the tire, and the tire slip angle, or angle of attack relative to the direction of travel of the car.
The tire needs to be able to transition from the one direction of resistance (lateral, which is the resisting of the centrifugal forces which are at right angles to the direction of travel) to the other (longitudinal or inline acceleration associated with application of power) over a longer period of time in order to maintain grip with the surface of the track.
We can cause the car to produce...
We can cause the car to produce rear steer to the left to tighten the car while accelerating off the corners for more forward bite by staggering the heights of the trailing links. If the right trailing arm is mounted higher than the left-side arm, then as the rearend rotates, the LR tire will move to the rear more so than the RR tire resulting in rear steer to the left.
If this transition happens too quickly, the tire is "shocked" and will most likely break loose. This is very detrimental to performance because in order to recover the grip in the rear tires, we must back off the throttle and allow the tires to reattach themselves to the track surface. This takes a lot of time and we lose a lot of ground in the process.
The pullbar or lift arm can absorb some of the torque going to the tires during initial application of power. By being able to move, these devices will absorb of some of the torque of the motor for a short period of time, usually long enough to allow the tire to adjust to the new direction of force.
We can experiment with different rates of springs and shocks in these systems to adjust to and perfect the traction enhancement for different conditions. Higher amounts of grip in the track surface mean more spring rate is needed in the devices. Slicker track conditions require less spring rate and more travel for increased torque absorption.