The contact area between a tire and the road is called the tire footprint and is shown by Ap. At any point of a tire footprint , the normal and friction forces are transmitted between the road and tire. The effect of the contact force can be described by a resulting force system including force and torque vectors applied at the center of the tire footprint. The area of the tire footprint is inversely proportional to the tire pressure. Lowering the tire pressure is a technique used for off-road vehicle in sandy, muddy. or snowy areas, and for drag racing. Decreasing the tire pressure causes the tire to slump so more of the tire is in contact with the surface, giving better traction in low friction conditions. It also helps the tire grip small obstacles as the tire conform more to the shape of the obstacle, and makes contact with the object in more places. Low tire pressure increase fuel consumption, tire wear, and tire temperature. In most vehicles, the front and rear tires will wear at different rates. So, it is advised to swap the front and rear tires as they wear down to even out the wear patterns. This is called rotating the tires. Front tire, especially on front-wheel drive vehicles, wear out more quickly than rear tires.
Figure1 Tire footprint**
** Figure Ref. http://www.aircti.com
Thanks for the information about tire pressure on roads and tire footprint. Tire footprint calculation is based upon the soil and the tyre. The formula for calculating tire footprint is Footprint = (Vehicle & load weight/# of tires) / Tire Pressure in PSI. This formula gives the result in square inches. The tire pressure decides everything and its based on the rotations of the tires on roads. read more
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