Legal limit not safe says research
Independent research undertaken by MIRA -- the Motoring Industry Research Association -- reveals that braking performance deteriorates in wet conditions when tyre tread depth drops below 3mm.
Although the legal tread depth limit is 1.6mm, a threshold set by motoring experts some 13 years ago, industry-supported road safety group RoadSafe said there is now "compelling evidence" that motorists should check and change their tyres at 3mm. Road accidents where wet conditions are a contributory factor are on the increase, said the group.
It's only fair to point out, though, that members of Roadsafe stand to gain if motorists follow their advice.
The trend is already upwards according to Town and Country Assistance who said that road accidents where wet conditions are cited as a major cause have increased from 1 in 12 in 1998-99 to 1 in 4 in 2003-04.
“There has been a long-standing belief within the motoring industry that wet weather tyre performance deteriorates more rapidly as the tread depth wears away. A comprehensive test of different vehicles and tyre tread depths now scientifically confirms these claims,” says MIRA’s senior engineer, Simon Aldworth, who carried out the research into tyre wet grip performance at the organisation’s headquarters in Nuneaton.
MIRA’s research was carried out on four separate vehicles, a mid-range family hatchback, an MPV, executive saloon and a high performance saloon car, measuring stopping distances at 50 mph in conditions that represented moderately heavy rain (0.5mm to 1.5mm water depth). The research discovered that tyres with a 3mm tread had a 25 per cent better performance than those at 1.6mm.
In terms of stopping distance this represents an extra eight metres (25ft) in wet conditions. In one test, when a tyre with a tread depth of 8mm was compared to one with only 1.6mm, the stopping distance increased by 13 metres (42.25ft).
“No-one is suggesting that 1.6 mm tyre tread depth is not safe,” says Adrian Walsh. “However with 300,000 crashes every year and a climate which is now much more susceptible to heavy rain, particularly in the summer months, there is a need to take action now. If motorists replaced their tyres sooner stopping distances would improve, accidents would reduce and lives would be saved. With over 3,500 road deaths a year, what bigger incentive can there be to replace tyres more frequently?”
It’s also a view that several car manufacturers hold and they specify in their owner manuals that tyre performance and safety margins decrease once the tread depth reaches 3mm, owing to a reduction in grip and an increased rise of aquaplaning.
On the back of this research, RoadSafe is supporting an autumn campaign to educate motorists on tyre safety and encourage more frequent tyre replacement. RoSPA, which is also lending its support to the campaign, is advising motorists of a four point tyre health check to help increase driver safety:
Every two weeks check the pressure of your tyres when they are cold.
Check the tread depth of your tyres. Although the minimum legal UK tread depth is 1.6mm, RoSPA recommends that tyres should be replaced when the tread depth reaches 3mm. As the depth decreases stopping distance in wet weather will increase. This is more notable on cars with larger wheels and wider tyres.
Check tyres for damage. Look out for any cuts, cracks or bulges as these can lead to slow punctures and blowouts.
Finally, don’t forget to check the pressure and tread depth of your spare tyre.
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