Circle Of Traction Theory

Circle Of Traction Theory

What is circle of traction theory?
The circle of traction theory is a way to express how much traction is available for a given type of tire. The image above is a visual representation of the circle of traction. When you have a tire on the racing surface there is a certain contact patch that is generated between the tire and the surface depending on the load that the tire is asked to support. Tires have more traction available as vertical load increases, but this tapers off after a given point. Depending on the force applied, the components that the tire is constructed of – and the steering input applied generating slip angle your tires contact patch has a place in this circle of traction. The more force you apply with your accelerator pedal (represented as climbing higer on the acceleration force line in the circle (red line) ) the contact patch moves towards the total capability of the tire (outside of the circle). The more steering input (blue line) that is applied- the more the force travels along the force line for turning right. Where these two intersect is where your contact patch is on that circle of traction. If you go to extremes on any force applied like a full throttle acceleration or a up against the lock steering turn you can see how your contact patch travels outside that capability circle. When this occurs is typically when your butt muscles tighten up a little bit because your car has lost control.

How can I see or feel the circle of traction? 
    A very easy way to prove to yourself how this traction circle exists (if you have never lost it in a race car) is to take your car to an empty parking lot and go in a circle slowly applying more and more throttle until the tires just begin to squeal. Back off your throttle until just barely until the tires just quiet. Maintain this speed and then slowly apply your brake pedal while maintaining that speed. You will hear your tires begin to squeal again. The braking force added to the maxed acceleration force and turning force exceeds the traction circle quickly. This is why your very fastest laps are usually generated when your braking is done before the apex of the corner. If you have braked, let your car settle, negotiated the turn and then accelerated there is more traction available because of the lesser number of forces being applied at any given time.
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