Cars Simplified

Contact Patch

The area which the tire is in contact with the ground at any given moment is considered the contact patch. When in motion, the rotating tire is constantly changing the surface area location of its contact patch, and other forces and conditions shape it.

Tire pressure, for example, often changes the level of contact the center has, in relation to the sidewalls. Camber can change which side of the tire contacts the road more, which will also have an effect on which side will wear down faster. The vehicle's weight pushing down on the tires, as well as the downforce generated by the vehicle's body at a high enough speed can also change the contact patch. The suspension can alter the weight shifting characterists, trying to keep a large contact patch on all four tires as a turn is made at considerable speed.

Racing Applications

In racing, the contact patch characteristics are typically measured by checking the heat levels on the inside, middle, and outside of the tire's tread. Higher heat is a result of higher levels of friction, and uneven heat levels mean the contact patch is uneven. If the middle of the tread is the hottest, the tires are likely overinflated, causing the center to bulge. If the outside is hotter than the inside, that usually means there is not enough camber resisting the sideways roll effect of the tire through the turns.

Because the vehicle is not constantly turning the same amount and in the same direction (with the exception of drag racing), it is impossible to give the vehicle a perfect contact patch in every turn. The engineers on each team try to determine the best trade-off for all the turns on each particular track.