Skid Resistance of Passenger Car Tires on Wet Surfaces

Abstract

Abstract This paper reports investigations into the effect of tread pattern, pattern modifications, tread material, and tire casing construction, on skid resistance of passenger-car tires at speeds between 25 and 80 mph on a range of wet road surfaces. The technique was to brake the front wheels of a car until they locked, and to record deceleration of the vehicle. From the deceleration record, both peak and locked-wheel values of braking force coefficients were obtained. The method is described and an assessment of the errors is given. The experiments showed the importance of adequate drainage of the region of contact between tire and road, particularly at higher speeds, in order to remove the lubricating film of water. Such drainage can be provided either by a tread pattern or a coarse road surface. The results indicate the importance of each and their inter-relation. Results of various modifications to a standard tread pattern are given; these show that on smooth surfaces worthwhile increases in wet road adhesion at high speeds can be obtained by suitable design of tire tread patterns. Magnitude of increases in friction due to changes in tread material are given for both peak and locked-wheel coefficients. Ratios of peak to locked-wheel coefficients have been calculated over a wide range of surface and tire combinations. They show the potential value of devices enabling a vehicle to make use of these high coefficients.