The Role of the Tread Pattern — A Blend of the Simple and Complex

Abstract

Dry traction and wet traction respond to tread design in opposite fashion. Traction coefficients obtained under dry conditions are lowered by the presence of a tire tread pattern, but are increased by a pattern under wet conditions. The lowering of the friction coefficient on dry surfaces is related to the amount of void area in the total contact patch. Under wet conditions, however, the vital role of the tread pattern is to facilitate the removal of water from between tread and road surface. This is accomplished by providing localized high pressure points and sharp edges for rapid contact and by providing channels for either water drainage or to serve as water reservoirs. The role of row number, row width, sipes, groove distribution and groove angle are reviewed. The complexity of the tread surface picture has so far defied detailed analytical dissection. However, a rudimentary view from a hydrodynamic approach is outlined.