Why tread depth matters

[Satch]

Been posted up a number of times that people with newer summer tyres are doing OK, how some people here chop tyes at 3/4mm remaining tread depth and how winter tyres start giving up being fully effective at 4mm.

At work yesterday I had an exchange of views with someone who was moaning that they had skidded into tree despite having "loads of tread left" on tyres that he says have done 18,000 miles

This is why:

Contact area comparison with various groove depths of a summer tyre. Driving speed 75 km/h, 3 mm of water on the road.

"When the driving speed increases and the tyres wear out, the contact area between the tyre and the road is dramatically reduced. The figure shows the size of the contact area of a summer tyre with various groove depths, with a water thickness of three millimetres and driving speed of 75 km/h. The contact area of a vehicle with worn-out tyres, thread 1.6 mm, is only 16 per cent when compared to a stationary vehicle."

That applies in spades for snow/slush conditions



8mm Tread depth

4mm Tread depth

1.6mm Tread depth

Slush and aquaplaning