Measurement of Water Film Thickness Due to Sipe Edges of Studless Tires

ABSTRACT Water on an icy surface is wiped by the rubber sipe edges of studless tires. However, it has been proposed that water on an icy surface forms a thin film rather than being removed completely. Nonetheless, there have been relatively few studies on the contact conditions of rubber sipe edges and the formation of a water film due to wiping. In this study, the frictional properties and contact areas of model sipes of studless tires were measured. In addition, the thickness of the water film formed on the tread surface was estimated by optical interferometry. Three types of styrene butadiene rubber with different levels of hardness were used as rubber specimens. The experiment was conducted by varying both the number of rubber edges and the slope angle between the rubber specimens and the vertical direction of a glass disk. The coefficient of friction tended to decrease with increasing sliding speed at all slope angles, and the value of the coefficient of friction was decreased as the slope angle became large. Moreover, the contact area between the rubber edges and a glass disk with a slope angle of 0° tended to increase as the sliding speed increased. The thickness of the water film formed after wiping ranged from 0.98 to 1.70 μm, and it increased as the slope angle increased.