Driving with worn tyres in winter could be more dangerous than drink driving.

That’s the conclusion of a new study by the Centre for Automotive Industry Research at Cardiff University.

Driving a car with tyres that are at the legal limit of 1.6mm of tread can increase braking distance by over a third. That’s compared to tyres in good condition with 4mm or more of tread.

Slippery slope

The new research is a first in comparing the impact of both worn tyres in wet, winter weather conditions and alcohol consumption on stopping distance. It has found that driving with worn tyres increases additional stopping distance seven times, as much as being over the drink drive limit.

Professor Peter Wells of the Centre for Automotive Industry Research at Cardiff University led the research, which was commissioned by Halfords.

It raises the question as to whether the legal minimum limit for tyre treads is too low. Current regulations on tyre tread have not been updated since 1986. Most road safety practitioners have long believed the limit should be set at 3mm as opposed to 1.6mm.

One for the road

Professor Wells found that on average, consuming alcohol increases reaction time by 18% or 120 milliseconds. At 70mph, this would lead to an increased stopping distance of 12.4 feet.

However, the difference in stopping distance between tyres in ‘good’ condition (4mm of tread) and  and those with just 1.6mm tread is 36%. This equates to an additional 89ft.

“Braking distances are an indicator of general levels of grip. 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.

Worrying attitudes to safety

Graham Stapleton, CEO of Halfords believes that the study demonstrates that the current legal limit on tread is too low.

Last year Halfords saw over 100,000 motorists who’d received a warning for the state of their tyres decide to leave them unchanged. Generally the advice came in the form of tread depth advisory note – technically they passed the MoT, but would likely need changing before the next MOT.  Worryingly, many were unlikely replace them until their next MOT.

“Every year we advise huge numbers of UK motorists,” says Stapleton. “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.

“A tyre with just 1.6mm of tread could be one small lock up or pothole away from being illegal and this could even happen on the way back from the test centre,” he adds. “This study clearly demonstrates that current tread limits are just too low given how much grip is reduced, even when within legal limits. ”