Stopping distances could be more significantly affected by worn tyres than drunk driving, according to a new study.

Tyres with a tread depth at the legal limit of 1.6mm had the potential to increase braking distance by over a third compared to tyres in good condition. For the first time the research compared the impact on stopping distances of worn tyres in wet, winter conditions with alcohol consumption. The report was commissioned by Halfords and conducted by the Centre for Automotive Research at Cardiff University.  

Professor Peter Wells was the lead researcher on the report and he found that drinking alcohol increases reaction time by 18%, which at 70 mph would lead to an increased braking distance of 12.4 feet. Stopping distances were compared between tyres with a tread of 4mm and those at 1.6mm, and the difference in reaction time was 36%, equating to a further 89 feet. So worn tyres affected stopping distances over seven times more than a driver being the influence of alcohol – an alarming and perhaps surprising conclusion.

“Braking distances are an indicator of general levels of grip”, said Prof. Wells. “So, if worn tyres increase braking distances by a third, we can reasonably assume that general levels of grip in the tyres are reduced by this amount too. Therefore, worn tyres will also have a significant impact on car control on the road in other situations, such as cornering. This means it is more likely that you’ll lose control of the car in the first place if you have worn tyres,” Wells said.

Other information contained in the study was equally concerning. Halfords revealed that over 100,000 drivers who had received an MOT advisory note about the tread depth of their tyres did nothing about it immediately. Advisory notes are given when tyres are close to the legal limit but still above it. However, they are likely to be below the legal limit by the time of the car’s next MOT.

Graham Stapleton, the CEO of Halfords, said: “Every year we advise huge numbers of UK motorists that their tyres are dangerously low on tread, but unfortunately many drive away assuming that, if they’re legal, they must be fine. But the reality is that their safety is already significantly compromised, and this will only increase as they experience more wear. Any tyres that receive a warning are likely to be illegal with just a few thousand more miles of motoring.”

Stapleton believes that the legal limit of 1.6mm is too low, having been unchanged for more than 36 years.

There is a simple check drivers can do to test their tyre tread depth. Take a 20p coin and place it in a groove of your tyre. If the rim of the coin is visible then the tread depth is below the legal limit.