Tread Depth and Safety
A new car tyre begins life with approximately 8mm of tread. The the minimum legal tread depth is 1.6mm, however most motoring organisations recommend changing at 2mm and the majority of tyre manufacturers recommend changing at 3mm.
As the tread depth reduces, the tyre's ability to remove water from the road surface reduces, increasing the risk of aquaplaning because the tyre is unable to transmit traction and braking forces to the road as effectively. Therefore the vehicle's stopping distance increases.
Although the legal minimum tread depth is only 1.6mm, independent research at MIRA shows that tyres with 3mm of tread have an average 25% better performance than those at 1.6mm - which represents an extra 8 metres stopping distance in wet conditions.
You can check how close you are to the legal limit on all tyres by looking for the treadwear indicators:
These indicators are small raised areas at the bottom of the grooves. Once the surface of the tread rubber is level with these raised areas, the tyre tread depth is approaching the legal limit of 1.6mm and you should have your tyres checked and replaced.