All the evidence supports the fact that in the wet, the deeper the tread you have, the more grip you have. So why do we say 3mm? Why should the recommendation not be 4mm or 5mm of tread depth? Extensive testing has shown that 3mm is the depth at which the performance of the tyre begins to drop off significantly.

Data from Continental's tests at the MIRA October 2004.

MIRA is the Motor Industry Research Association 

Several police forces already change the tyres on their vehicles at 3mm, supporting our call for motorists to consider changing their tyres at 3mm, to make our roads safer for everyone.

Results of Auto Express 1.6mm vs 3.0mm tread depth tests

This study was undertaken at MIRA's proving ground near Nuneaton, Warwickshire. The facility has a wet-weather test track which is covered with asphalt and offers similar grip and drainage properties to a motorway surface. The accompanying video evidence can be viewed here.

Each car was fitted with sets of tyres ground down to exactly 3mm, and 1.6mm using a painstakingly accurate technique. Repeated brake tests were performed for each model, using Racelogic VBox timing equipment to measure stopping distances from 70mph under full ABS braking to the nearest cm.

Data from Auto Express tests at MIRA June 2006