- Optionally, tires with a maximum speed of over 149 mph (240 km/h) may have "ZR" in the size description depending on the manufacturer (e.g. 245/40 ZR 18).

The service specifications consist of load bearing index 5 and speed rating 6.

 - If the size description of your tire includes "ZR" and there are no service specifications, ask the tire manufacturer in order to find out the maximum speed.

If a service specification is available, the maximum speed is limited according to the speed rating in the service specification.

Example: 245/40 ZR 18 97 Y. In this example, "97 Y" is the service specification.

The letter "Y" represents the speed rating and the maximum speed of the tire is limited to 186 mph (300 km/h).

 - Every tire that has a maximum speed above 186 mph (300 km/h) must have "ZR" in the size description and the service specification must be given in brackets.

Example: 275/40 ZR 18 (99 Y). The speed rating "(Y)" shows that the maximum speed of the tire is above 186 mph (300 km/h).

Ask the tire manufacturer to find out the maximum speed.