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In dragracing a rear wheel drive (RWD) car, the total rear wheel loading, during launch, is of great importance since it...along with the effective friction coefficient of the rear tires...determines the maximum acceleration. This total loading consists of the sum of the static loading and that loading which is "transferred" from the front of the car (the "weight transfer"). Obviously, then, the total loading cannot exceed the total weight of the car.
(Actually, total loading CAN exceed the total weight of the car, but, since this occurs in such a short time period, it is only of academic interest. This effect is most pronounced when very low rate suspension springs are used at the front and the car squats excessively. The resulting inertial moment, as the car rotates, initially reduces weight transfer, but, as the car reaches its extreme position, there is a momentary rear tire loading which can exceed the total weight of the car. Again, this happens over an extremely short time period and should not be sought as a performance advantage.)
If you are relying on a static preloading to achieve equal rear tire loading on launch, it is essential that you know the weight transfer. Again, if BOTH front wheels are pulled on launch, you know that the weight tranfer is equal to the static loading of the front wheels. If this is not the case, however, static preloading cannot be accurately determined.
And, if you are trying to make sense of the output from traction dyno tests, it is again essential that you know the maximum weight transfer during launch.
The following spreadsheet allows calculation of the weight transfer. (See another page for calculation of the friction coefficient.):