Sealing is at the Origin of Rubber Slipping on Wet Roads

TL;DR

This paper proposes a novel mechanism where rubber sealing water-filled pools on wet roads reduces surface asperity effects, explaining the observed loss in tire-road friction at low speeds.

Contribution

It introduces a new physical explanation for wet-road slip involving sealing of water pools, supported by theoretical calculations and experimental data.

Findings

Water sealing reduces substrate roughness and friction.

Predicted friction loss matches observed 20-30% reduction.

The mechanism explains low-speed tire slip on wet roads.

Abstract

Loss of braking power and rubber skidding on a wet road is still an open physics problem, since neither the hydrodynamical effects nor the loss of surface adhesion that are sometimes blamed really manage to explain the 20-30% observed loss of low speed tire-road friction. Here we advance a novel mechanism based on sealing of water-filled substrate pools by the rubber. The sealed-in water effectively smoothens the substrate, thus reducing the viscoelastic dissipation in bulk rubber induced by surface asperities, well established as a major friction contribution. Starting with the measured spectrum of asperities one can calculate the water-smoothened spectrum and from that the predicted friction reduction, which is of the right magnitude. The theory is directly supported by fresh tire-asphalt friction data.