Dimension designation for tyre

Updated 06/08/2023

Designations for tyre dimension, load index and speed rating.

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, such as: 255/40 R19 100 W.

255	Tyre width (mm)
40	Ratio between tyre wall height and tyre width (%)
R	Radial ply
19	Rim diameter in inches
100	Codes for the maximum permitted tyre load, tyre load index (LI)
W	Speed rating for maximum permitted speed, speed rating (SS). (In this case 270 km/h (168 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 chosen, the car must not be driven faster than the speed rating of the tyre (for example, class Q can be driven at a maximum of 160 km/h (100 mph).) The top speed at which the car can be driven depends on road conditions, not the speed rating of the tyres.

Note

The maximum permitted speed is specified in the table.

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)

Warning

The lowest permitted load index (LI) and speed rating (SS) for the tyres for each respective engine variant are shown in the car's registration document. If a tyre with too low a load index or speed rating is used, it may overheat and be damaged.