"It is amazing how may drivers, even at the Formula One Level, think that the brakes are for slowing the car down." - Mario Andretti
This is a famous quote that brings attention to the critical aspect of "dynamic weight transfer" in the process of making the race car handle.
The art and science of getting a race car to go through turns at maximum speed is greatly related to using throttle and brakes to move weight from the rear to the front tires and vice versa.
Reducing throttle or "lifting" causes weight to transfer from the rear tires to the front. The same weight transfer occurs when applying brakes. Adjusting shock damping rates will affect the speed at which the weight transfer occurs.
Similarly, releasing the brakes will allow weight to move back to the rear. Applying throttle will move weight from the front to the rear.
All this weight transferring is for the purpose of helping the car to turn (rotate) with the least amount of lost speed.
There is no place where this process is more critical than where a track has a "diving turn". One example of a high speed "diving turn" is T2 at Mosport. Another is T1 at Interlagos. Another, but less obvious one is the T4-T5 Esses at Road Atlanta. A slower speed "diving turn" is the Corkscrew at Laguna Seca.
A diving turn presents a special challenge. As the front tires crests and begins to "fall" down the hill, the weight on the front tires and hence the grip is substantially reduced. This is followed rapidly by the rear tires cresting the hill where grip is reduced further. Often the driver will introduce steering to compensate for understeer on the lighter front and is surprised by a sudden oversteer just after the rear tires crest the hill.
On a car with wings, one can increase grip by creating more downforce, but still the effect of the diving is to reduce grip from its maximum "pre-dive" level.
So, the "trick" is to use throttle and/or brake to cause downward momentum of the front, forcing the tires to better follow the terrain, just at the moment the front tires crest the hill. This is quickly followed by throttle application to counteract the loss of weight on the rear as those tires crest the hill and the car begins it's turn. This is more complicated if the turn is part of a braking zone, like Interlagos and Laguna where it is a matter of modulating brake input to adjust the weight transfer from rear to front, and then followed by modulation of throttle.
Get the timing of this process right, and the speed through the corner is remarkably increased.
So, as alluded to by Mario, brakes and throttle are tools not just for slowing down and speeding up--they are tools to be used to make the car turn--just as important as the steering wheel.
For those like me that really are fascinated by the complexity of vehicle dynamics--here is a link to an interesting presentation...pay attention to the "polar moment of inertia" concept:
Load Transfer Dynamics
