- David Hort
Should tyres be changed at 3mm?
The current legal limit for tread depths on UK tyres is dangerous and UK motorists are being urged to change their tyres at three millimetres rather than the prescribed 1.6mm, says a leading tyre manufacturer.
Continental Tyres says that the current legal tread depth of 1.6mm means that tyres will perform at just 55 per cent efficiency when compared to cars with a full tread of eight millimetres – with serious consequences for UK in the event of heavy braking or emergency manoeuvring, particularly on wet roads.
At 50mph a car with a road-legal tread depth of 1.6mm will take an additional 13 metres to stop in wet conditions compared to eight millimetres, says Continental.
The same car – with 1.6mm tread - at 70mph would take an additional 37.5 metres to stop in wet conditions.
Continental tyres is urging UK road users to change their before reaching the legal limit of 1.6 millimetres because of the safety repercussions of lower tread depths.
Despite the legal limit for tyre tread depths standing at 1.6mm, government and emergency service vehicles change their tyres at three millimetres because of safety concerns.
Whilst dry handling is still a concern for tyres with reduced tread, it is in the wet where the additional stopping distance becomes more concerning.
A tyre’s tread pattern is designed to displace standing water when driving in the wet, meaning at eight millimetres the tyre is able to disperse the maximum volume of water from the road without using up all of its tread capacity.
However, as the tread is worn down its capacity decreases, which means less water can be displaced, leading to a build up of water in front of the tyre.
As that water builds up, so does the pressure acting on the front of the wheel and, in some cases, the pressure can be great enough to lift the tyre off the road; commonly known as aquaplaning.
According to Continental, 80 per cent of motorists admitted that they were aware that their tyres had deteriorated to a state where stopping distances and braking had been affected, but still hadn’t changed them.
It’s a point that was flagged up by the AA seven years ago when its foundation advised motorists of the problems associated with reduced tread depth.
“When the tread depth reaches 3mm, take care to monitor the tread depth that remains since tyre grip on wet roads is markedly reduced below this depth.
"Ideally replace your tyres soon after the tread depth reaches 3mm," said the AA.