31/05/2011

What exactly do the figures and letters on tyres mean?

“175/55 R 13 87 T”, for example, reveals that the tyre is 175 millimetres wide. The number 55 after the slash says that the side of the tyre is only 55 per cent of its width. The letter R stands for radial, i.e. the design of the tyre. The number after the design letter, i.e. after the letter R in this case, is the rim diameter. Here it is 13 inches. The number 87 stands for the load-bearing index; this indicates the maximum load the tyre can bear. There is a table with these figures. 87, for example, stands for 545 kilograms. The letter T at the end stands for the maximum permissible speed. In our example, this is 190 km/h.

The letters M+S may also appear. They stand for mud and snow and can be found on car tyres that are suitable for use in winter.
Car tyres have other letters and numbers on them in addition to this mandatory information. TL indicates that the tyre is tubeless. TT means that the tyres have a tube. If there is a T before the tyre width, this means “temporary use” and indicates an emergency tyre. The top speed needs to be observed here! DOT ... 2510 provides information about the date when the tyre was manufactured; it is shown in the last four figures of the DOT number. In this case, the 25th week of 2010. Retread tyres are identified by the capital letter R (retread) on the side. If the vehicle licence includes XL or Reinforced after the tyre size, reinforced tyres with a particularly high load-bearing capacity are required.