On the first page of this site, in the "Getting Started" section, I present this picture of the forces acting on a car as it accelerates, pointing out that the product of forward thrust and center of gravity height equals the product of weight transfer and wheelbase. In addition, there is a balance of horizontal and vertical forces.
Actually, I say it is not a car, but a steel plate cut out in the shape of a car. I did this because I wanted to avoid a discussion of transients. At this point, however, I feel it necessary to "open this can of worms."
Transients, in this case, refer to the force and moment conditions which exist as actual vehicle components "move" during the first few milliseconds of launch.
Consider, for instance, a case in which the thrust vector at the rear tire patch has no vertical component. In other words, the instant center is at ground level. Since there is no net vertical force in the suspension links and...at time zero... there is no change in the spring loads, moment and force balance is achieved as indicated:
That first picture is still correct, of course. We will have to wait, however, until the car has "taken a set" before it becomes reality.
In the meantime, this zero percent antisquat car experiences NO weight transfer at time zero. That clockwise inertial moment indicates that the car is being rotated counter-clockwise, meaning that the rear springs are going to be eventually compressed. Remember: At zero percent antisquat, ALL of the weight transfer is carried through the springs.
If, instead, the car has 100% antisquat, all of the weight transfer is carried through the suspension links. This would be a situation approaching that represented by the steel plate I used in the "Getting Started" section. Though the front of the car would be moving up as the front springs extend, the rear of the car would be essentially solid, with the full weight transfer carried through the links. But, we still have the rear tires to consider. They must, at time zero, take the full weight transfer load.
And, it is in the manner in which the load is applied to the rear tires that we might find a difference in launch performance. At 100% antisquat, the full weight transfer is taken by tires at essentially time zero. At zero percent antisquat, the weight transfer to the tires starts at zero at time zero and increases to full value as the rear springs are compressed. With an antisquat value of, say, 40%, 40% of the weight transfer would go to the tires at time zero with the rest applied during the time required for the springs to be compressed.
Is it possible, then, that optimum launch performance requires an antisquat compromise? 100% antisquat minimizes oscillatory loading, but, if the tire performance is adversely affected by the sudden load application, it is conceivable that it might be necessary to accept some oscillatory loading. It is reported that antisquat values over 100% are commonly used by street/strip cars, but the very high horsepower pro mod cars stay well below 100%. The question, of course, is whether this is the result of controlled experimentation or simply a case of "running what the winner runs." Perhaps, if the instant center "out" can be placed far enough forward, these perceived problems (with high antisquat percentages) will suddenly disappear.
Is there a reason for compromise? I remain very cautiously open to the possibility.