What Is Meant by Speed Rating?
The speed rating of a tire indicates the speed category (or range of speeds) at which the tire 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 tires at standardized speeds. A letter from A to Z symbolizes a tire’s certified speed rating, ranging from 5 km/h (3mph) to above 300 km/h (186 mph). This rating system, listed below, describes the top speed for which a tire is certified. It does not indicate the total performance capability of a tire.
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 tire could achieve.
As manufacturers made more tires 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 tire 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 tires. Speed rating is identified as a part of the tire’s sizing or service description.
In the latest attempt to standardize tire designations, all ratings except Unlimited ZR incorporate the speed symbol and load index as the tire’s service description. For example:
|205 = Section Width in Millimeters|
|60 = Aspect Ratio|
|R = Radial Construction|
|15 = Rim Diameter in Inches|
|91 = Load Index||(Service Description)|
|V = Speed Symbol|
When “ZR” appears in the size designation with the service description, the maximum speed is as indicated by the service description:
|Tire Designation||Maximum Speed|
|P275/40ZR17 93W||270 km/h (168 mph)|
|P275/40ZR17 93Y||300 km/h (186 mph)|
For tires having a maximum speed capability above 240 km/h (149 mph), a “ZR” may appear in the size designation. For tires having a maximum speed capability above 300 km/h (186 mph), a “ZR” must appear in the size designation. Consult the tire manufacturer for maximum speed when there is no service description.
|Speed Symbol||Speed (km/h)||Speed (mph)|