After four winters it's time for a change - winter tyres should not be used for more than four winter seasons and should have at least four millimetres' tread depth at the start of the season. Tyres that are older lose the very suppleness they need in winter at low temperatures and insufficient tread depth reduces traction in snow and ice. Tyres age through the effects of the weather and storage - with time, the antioxidant agents in the tyre reach the tyre surface. This process is accelerated when tyres are stored during the warmer months, as the protective waxes which prevent this effect on brand new tyres get worn away as the tyre is used.

As a result, winter tyres gradually lose the suppleness they need for use at low temperatures. Braking distances get longer and lateral guidance deteriorates. That's why these dedicated winter tyres should be replaced after four winters at the latest. The tread depth also deserves some attention. If the tread depth on the tyres is less than four millimetres, it's time for a new set. Once winter tyres have gone below this depth, their winter characteristics - i.e. grip in snow and ice - deteriorate considerably. It's easy to check - once the gold edge of a 1 euro coin is only just covered or if it is actually visible, then the tread depth is less than four millimetres.