<Ul> <Li> The larger the load on the tire, the larger the contact patch . </Li> <Li> The larger the inflation pressure, the smaller the contact patch . </Li> </Ul> <Li> The larger the load on the tire, the larger the contact patch . </Li> <Li> The larger the inflation pressure, the smaller the contact patch . </Li> <P> These two properties are not linearly proportional to the area of the contact . For example, a 10% change in load or inflation pressure usually does not result in a 10% change in the contact patch area because the load or pressure on a tire can be altered freely, and the contact patch area is affected by the tire geometry and stiffness . Further, the size of the contact patch cannot be simply calculated as load divided by inflation pressure, and the average contact pressure a tire has with the road surface is not equal to the inflation pressure . </P>

How much of a car tyre is in contact with the road at 30mph