Dimension designation for tyre
The car has an approval for the complete vehicle with certain combinations of wheel rims and tyres.
Designation of dimensions
All tyres have a dimension designation, for example: 235/55 R18 100V.
235 | Tyre width (mm) |
55 | Ratio between tyre wall height and tyre width (%) |
| R | Radial ply |
18 | Rim diameter in inches |
100 | Codes for the maximum permitted tyre load, tyre load index (LI) |
V | Speed rating for maximum permitted speed, speed rating (SS). (In this case 240 km/h (149 mph).) |
Load index
Each tyre has a certain capacity to carry a load, a load index (LI). The car's weight determines the load capacity required of the tyres.
Speed rating
Each tyre can withstand a certain maximum speed. Tyre speed rating, SS (Speed Symbol), must at least correspond with the car's top speed. The table below shows the maximum permitted speed for each speed rating (SS). The only exception to these regulations is winter tyres1, where a lower speed rating may be used. If such a tyre is selected, the car must not be driven more quickly than the tyre is rated for. For example, cars with Q rating tyres must be driven at speeds not exceeding 160 km/h (100 mph). The road conditions and applicable road traffic rules determine how quickly the car can be driven, not the speed rating of the tyres.
Note
| Q | 160 km/h (100 mph) (used only on winter tyres) |
| T | 190 km/h (118 mph) |
| H | 210 km/h (130 mph) |
| V | 240 km/h (149 mph) |
| W | 270 km/h (168 mph) |
| Y | 300 km/h (186 mph) |