The author reports on a MIRA demonstration to test the braking performance of tyres of differing tread depths in simulated, wet road conditions. Five sets of test cars with tyres of tread depths ranging from 1 to 8 mm were used to test the hypothesis that the greater the tread depth, the shorter the stopping distance. Tyres with a 3mm tread performed 25% more effectively in the wet than those of 1.6mm. In the UK, legislation defines a minimum tread depth of 1.6mm. RoadSafe, who laid on the demonstration, and the British Rubber Manufacturers' Association recommend that the minimum depth should be increased to 3mm. The stopping distances quoted in the Highway Code are out of step with modern braking technology. The relationship between skidding, insufficient tread and legislation is considered.
Abstract