Factors Affecting the Friction of Tires on Wet Roads

The object of the investigations described in this paper is to put in perspective the relative roles of the “drainage” and “energy loss” properties of tires in providing good adhesion on wet roads. Different aspects of tread pattern design and tread material are considered in relation to factors external to the tire, the major ones being the influence of water depth over a range representative of conditions on the road, the interaction of road surface texture, and the effect of speed. The method of approach includes full-scale experiments on the British Road Research Laboratory's track using braked and rolling wheels under carefully controlled conditions, laboratory investigations of the viscoelastic properties of rubber together with rubber friction tests, and theoretical considerations linking the different aspects. This work should lead to a better understanding of the mechanism of tire/road adhesion on wet surfaces and in particular to draw the distinction between, and relative importance of, lubrication and aquaplaning.