Project: Tyre Tread Depth - Wet Braking

Reference: S0711/V6

Last update: 19/12/2008 16:25:50


The project objectives are:

. Investigate the applicability of the published reports detailed above to other vehicles and wheel/tyre combinations by comparing wet grip braking performance at a range of tyre tread depths from new tyres down to 1.6mm on not less than three section width tyres per vehicle, fitted to three vehicles.

. Carry out an Impact Assessment (IA) considering the implications, both positive and negative, of a change in minimum tyre tread depth. In particular on the one hand the potential for reductions in accidents, injuries, congestion and on the other the potential costs to consumers in buying tyres more frequently, the raw material / energy cost of producing those tyres and the cost to dispose of the redundant tyre.


The legal minimum tyre tread depth across Europe for passenger car tyres has been set at 1.6mm across the central three-quarters of the tyre since the early 1990's. With modern safety systems such as Anti-lock Braking Systems (ABS) and Electronic Stability Control (ESC) becoming either standard fit on the majority of passenger cars in the case of ABS, or increasingly common on middle market models in the case of ESC, the tyre plays an integral role in systems in reducing the risk of loss of control accidents occurring.

This project is a collaborative research project between the DfT and the British Tyre Manufacturers Association (BTMA) which will investigate whether relative braking performance, for a range of passenger cars fitted with a range of available wheel and tyre combinations available from the factory, suggests that 3mm minimum tread depth is applicable across the broad spectrum of tyre footprints and tread designs in general use today and provide additional evidence.


Faber Maunsell
The Johnson Building, 77 Hatton Garden, London, EC1N 8JS

Contract details

Cost to the Department: £101,000.00

Actual start date: 01 May 2008

Actual completion date: 25 March 2010


Minimum Tyre Tread Depth for Passenger Cars Comparison of Wet Braking Performance
Author: MIRA
Publication date: 18/03/2010
Source: or MIRA Ltd Watling Street , Nuneaton, Warks. CV10 0TU. Tel. 02476 355000
More information:

Summary of results

  1. A series of objective tests were performed on MIRA's wet adhesion strailt line test surface to quantify the variation in tyre wet road grip with tread depth for a series of typical passenger car and tyre combinations. In addition, the effects of; an incorrectly fitted directional tyre, a deflated run-flat tyre, and reduced tyre pressures, on the wet braking performance have been determined.

    For the car and tyre combinations considered, the stopping distance performance at differing tread depths has been measured. The results illustrate that, generally statistically significant increases in stopping distance begin to manifest themselves at tread depths below approximately 3mm, although the magnitude of the increase is not consistent across all the car and tyre configurations.

    The stopping distances and the yaw stability of a vehicle fitted, firstly, with an incorrectly oriented directional tyre and, secondly, with a deflated run-flat tyre, were measured. In both cases no significant reductions in either braking performance or yaw stability were evident.

    The effects of tyre pressure reductions of 10% and 20% on the stopping distance and yaw stability of a vehicle have been measured. The results demonstrate that, whilst the yaw stability was unaffected, the stopping distance increased by between 5% and 11%.

    Statistical testing of the results has indicated a high degree of probability that the relative performance differences, where they exist, between the different tyre sets are 'real' and not due to 'chance'.