Vehicle skid tests: the effect of tire inflation pressure on the coefficient of friction

The coefficient of friction for a vehicle's tires sliding on a road surface is a critical parameter in calculating the speed of a vehicle involved in a motor vehicle collision. Theoretically, the amount of air pressure in the vehicle's tires and tread wear should not have a significant effect on the coefficient of friction between the tires of a skidding vehicle and the road surface. Skid tests were conducted to determine the effect of different tire pressures and tread wear on the coefficient of friction on an asphalt road surface. Each of the four tires on the vehicle were set to the same tire pressure for each skid test and were set from 45 to 5 pound per square inch (310.26 to 34.47 kilopascals). Various tire brands with varying age and tread wear were used for the tests. Average friction coefficient ranges for both wet and dry asphalt were measured. These values were compared to a hypothetical infinitely large data sample and no substantial difference was found regardless of the tire tread wear and tire pressure.