Abstract Three road tests of tires for tread wear were statistically designed. The design of test equalized the treatment of tires, and included a study of some of the factors influencing the road wear of tires in addition to the primary object of the test. Among these factors were the effects of vehicle, wheel position, day of test, climatic conditions, and length of storage. A study was made also of two methods of measurement-depth of tread grooves and weight loss. The information on these factors was obtained at no increase in cost of test. It was found that atire loses weight at essentially a constant rate, whereas, the depth of the tread grooves decreases at a declining rate, which results in a bias in the tread wear ratings. The weight method was also found to be more sensitive than the depth method. The study of the effects of vehicle and wheel positions led to the conclusion that differences in the rate of wear on different wheels do not affect the tread wear comparisons, since the rate in slow wearing positions is proportional to that in fast wearing positions, and the coefficient of variation is about the same. These results led to the conclusion that geometric rather than arithmetic averages be used in evaluating tread wear. The study of the effect of day of testing and of climatic conditions indicated that the surface temperature of the road and tire has a pronounced effect on rate of wear. Natural rubber treads containing channel black wore faster as the temperature increased, whereas, synthetic rubber tread containing furnace blacks wore faster as the temperature decreased. Other treads wore at about the same rate as the temperature changed. The effect of temperature on tread wear was greater in many instances than the effect of a lower coefficient of friction on wet roadways. Storage of tires generally increased the rate of wear; however, some treads did not wear faster after one year of storage. The object of one test was to determine the effect of type of rubber and black on tread wear. It was found that the rubber and black are mutually independent in their effects. The behavior of natural and synthetic rubbers or of channel and furnace blacks with a change in temperature made it impossible to compare them without stating the conditions of test.