When do I need to get new tyres for my car?
Metal rusts, bread becomes hard and mouldy, people get wrinkles and grey hair – the ageing process of these things catches the eye. But how do you recognise the age of a tyre? And how many years are the tyres allowed to go?
The DOT-Marking
All the data needed to determine its age can be found on the tyre itself. The so-called DOT marking (Department of Transportation – this marking of the American Ministry of Transport has established itself worldwide) can be found on the flank of every car tyre since 2000. A DOT number consists of four figures and is framed with a thin line. The first two digits indicate the production week; the third and fourth digits indicate the year of production. Examples :
If the DOT number is 1911, then the tyre was produced in the 19th week of the year 2011, therefore, sometime between 16 and 22 May 2011. If the DOT number is 0905, then this tyre comes from 2005, from late February or early March. This one would have been more than eleven years old. Tyres made before 2000 are marked with three figures and a special symbol. The first two digits here stand for a week of production, the same as in the four-digit number, and the third digit indicates the last number of the production year. A three-digit number without a symbol can be found on tyres produced in the 1980s. No one would ever use those tyres, though, even if they have not been used yet. Because the tyres do not get better with age as a good ham or wine do, for instance. Instead, the rubber becomes brittle, the grip isn't that strong anymore.
Signs of ageing
Apart from the mere date on them, tyres have various ways to age as the consequence of using them or even not using them at all. Of course, two-year-old tyres that rolled hundreds of thousands of kilometres make an impression of much older ones than the five-year-old tyres on the car of a retyree who drives weekly for a coffee party. Weather conditions, sunlight and ozone as well as mechanical stress leave their mark on tyres. Improper stocking also contributes to the ageing process, but with a different intensity.
Legal regulations
Anyone considering the purchase of a used tyre should be able to understand how stressed the selected tyre really is. And this knowledge also helps in deciding when to replace the tyres on your own car. There is a legal requirement for how old the tyres are allowed to be only for campers, trailers and carriages with speed limit of 100 km/h. The ADAC or the German Tyre Retailer and Vulcanization Trade Association (BRV) recommends an exchange for passenger cars not later than after ten years of use, but preferably after six years. But the wear limit is usually reached much earlier even with the regular driving intensity. Again, there are a few legal regulations, such as the prescribed minimum tread depth of 1.6 millimetres - which in turn is far too low according to ADAC and other organisations. Therefore, we can see that it is not enough to know all the legal requirements. When assessing the tyres, you will also need a bit of common sense.
So, what do I need to keep in mind?
The look at the DOT marking will do no harm. Thus, first of all, we find out the theoretical lifespan of the tyre. Now, it is still necessary to check its general condition. Is the tyre tread depth still sufficient? Summer tyres should have more than three millimetres of it, and it's four millimetres for winter tyres. For different tyres drive off differently, it is best to measure them several times and at different points. Are there visible notches or cuts? What about small age cracks? If the tyre is mounted onto a rim: Are there any rust marks or damage? There is almost no way to assess the storage conditions of the tyre. Eventually, the owner/seller can provide needed information.