A version of this article originally appeared in NASA SpeedNews in May of 2016
A wise man once said, “When driving at the limit, you steer with the pedals and control speed with the steering wheel.” At first this seems absurd but diving deeper into the mechanics of performance driving and vehicle dynamics will clarify its meaning. Consider that when cornering at the limit, any additional steering input will cause the car to understeer, which may or may not affect its turning radius but will certainly scrub speed. Additionally, when the steering is held fixed and additional throttle is applied the car will also understeer and track a wider arc. Alternately, when throttle is reduced the car tracks a tighter arc. This is the first and most important consideration when developing footwork skills: when the corning capabilities of the tire have reached their limit the throttle is the only tool left to change the direction of the car.
Ultimately, good footwork is all about controlling front-to-rear weight balance to maximize available grip. It is weight transfer combined with a change in speed that causes a car to track wider or tighter with throttle variation. Tires produce more grip as load increases so any forward weight transfer will give the front more bite and more steering and braking forces. Similarly, rear weight transfer reduces steering force but improves power traction forces.
Now let’s think about artificially reducing a tire’s capabilities; also known as “shocking” the tire. This happens when a tire is tasked with more force than it can support before allowing weight transfer to increase its grip. For example, trail braking into a corner and steering abruptly before allowing for weight transfer will overload the rear tires. Done properly, this initiates rotation. The same is true when powering out of a corner. Smooth, progressive throttle application causes the car to track wider and allows the rear tires to deliver maximum power. Abrupt throttle application can cause the rear tires to break loose under the same power if delivered before weight transfer occurs mid-corner. This can help the car steer out of the corner but may sacrifice power delivery.
Shocking the front tires occurs when the brakes are applied faster than the time required for weight to transfer to the front. Similarly, the front tires will lose grip abruptly if the brakes are released too quickly, resulting in rapid weight transfer off the front and to the rear.
In summary, proper footwork is all about weight transfer and balancing the forces on all four contact patches. Generally speaking, the driver’s feet should move as quickly as the suspension is able to move: street cars require slower, smoother inputs, while formula cars benefit from quicker inputs.