By now, you should know like the back of your hand that when the tread depth of your tyre is inferior to 1.6mm, you should replace your tyres immediately in order to avoid a fine or worse, an accident.
But are there other criteria that justify replacing your tyres? Is the fact that you've had them for five years justify their replacement alone?
The life of a tyre depends largely on your driving style. When all the criteria are met, the life of the tyre can extend beyond 5 years and 40 000 miles. In order to get there you need:
Even when all the conditions are met, rubber ages with the passing of time. It gets progressively covered with weather checking, starting from deep inside the grooves.
Tyres lead a hard life. They are confronted with sharp temperature variations, the forces involved in rolling, pollution, brake dust... all of which eat away at the rubber. As a consequence, the rubber loses in elasticity and weather cracking appears. Using your tyres regularly prevents early appearance.
So long as its stays superficial, weahter checking doesn't affect your safety negatively. However, it is a clear sign that the rubber is massively worn out. The loss of rubber elasticity means lower overall performance for your vehicle. Replacement becomes necessary.