What Is Meant by Speed Rating?
The speed rating of a tyre indicates the speed category (or range of speeds) at which the tyre can carry a load under specified service conditions. The speed rating system used today was developed in Europe in response to the need to control the safe performance of tyres at standardized speeds. A letter from A to Z symbolizes a tyre’s certified speed rating, ranging from 5 / (3) to above 300 km/h (186 mph). This rating system, listed below, describes the top speed for which a tyre is certified. It does not indicate the total performance capability of a tyre.
When this speed rating system was originally developed, the Unlimited V category of over 210 km/h (130 mph) was the top speed rating a tyre could achieve.
As manufacturers made more tyres that did not fit this category, it was necessary to better regulate performance at standardized speeds to ensure safety. The Limited V category of 250 km/h (149 mph) was then created, and the Z speed rating was added as the top speed rating that a tyre could achieve. W and Y limited speed symbols have been added as higher speed categories.
Always consult the manufacturer for the maximum speed of Unlimited Z tyres. Speed rating is identified as a part of the tyre’s sizing or service description.
In the latest attempt to standardize tyre designations, all ratings except Unlimited ZR incorporate the speed symbol and load index as the tyre’s service description. For example:
205/60R15 91V
205 = Section Width in Millimeters
60 = Aspect Ratio
R = Radial Construction
15 = Rim Diameter in Inches
91 = Load Index
V = Speed Symbol
When “ZR” appears in the size designation with the service description, the maximum speed is as indicated by the service description:
Tyre Designation Maximum P275/40ZR17 93W 270 km/h (168 ph)
P275/40ZR17 93Y 300 km/h (186 mph)
For tyres having a maximum speed capability above 240 km/h (149 mph), a “ZR” may appear in the size designation. For tyres having a maximum speed capability above 300 km/h (186 mph), a “ZR” must appear in the size designation. Consult the tyre manufacturer for maximum speed when there is no service description.
