Quantitative Measurement of Tire Flatspotting

Abstract Equipment was developed to measure the flatspotting of tires quantitatively on an indoor wheel. It provides close control over all of the important variables and has the virtue of simulating driving conditions for all seasons of the year. Good correlations between quantitative values from the indoor wheel and subjective jury tests on the road are obtained when wheel speeds are adjusted to give the same maximum tire temperature as in the road test for a given ambient temperature. The tire cord was of primary importance in controlling the depth of flatspot. Other variables exerted their influence via their effect on cord properties. For nylon 66 cord, flatspot depth was decreased by high ambient temperatures, high tire air pressure, low loads, and moderate run-in conditions. Change in the moisture content of the nylon cord improved or worsened flatspot depending on the ambient temperature of test. Factors such as cord processing conditions, cord twist, tire bias angle, number of plies, building dru...