Investigation of rubber friction on snow for tyres

Frictional behaviour of tyres on snow is important for vehicles. We made friction tests of rubber tread blocks, of different geometries and rubber formulations, on compacted artificial snow in a cold room using a linear tribometer. These tests show excellent agreement with outdoor vehicle tests. The friction coefficient (μ) for rubber decreases with increasing velocity because of a water layer formed by frictional heating. As glass transition temperature Tg of the rubber decreases μ increases, which correlates with the increased compliance of the rubber. At higher velocities siped tread-blocks show higher friction than blocks without sipes because of ploughing.