Tyred Out - For most drivers, a tyres life is over when the tread depth reaches the 1.6mm legal minimum. Thats great if you want to avoid a fine, but seriously flawed for preventing accidents.
Studies by the Motor Industry Research Association showed that in wet braking and cornering, the critical tread depth is around 3.5mm. From new until this point, a tyre has lost around 4mm of tread and less than 2% of it's wet braking ability. But for the next 2mm of wear they found that performance deteriorated by up to 35%.
In real terms, the 50mph to 0 stopping distance increased from 23.8m with the full 8mm of tread to 24.2m with only 4mm of tread. At the legal minimum of 1.6mm of tread it increased to 36.5m - a full 9m further than new tyres. That's two car lengths further - easily the difference between crashing or coming safely to a stop. The story is even more worrying on a concrete surface as you find on some motorways where the speeds are even higher than the 50mph brake test. With new tyres it took 5m further to stop than on tarmac and with barely legal tyres it took a massive 13m extra - about the length of a 40 tonne lorry!!
In order to test these results AutoExpress Magazine together with Roadsafe, took 4 Rover 75's and kitted them out with tyres with 8, 4, 3 and 1.6mm. The speed was set to 50mph and done on a soaked tarmac surface. They also did a test to see how cornering in the wet was affected by tyre wear.
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