Important: When replacing tires, never install a tire that is a smaller size or a lesser speed rating than that used as original equipment. The speed ratings only apply at the tire's full pressure. An under-inflated tire will not meet its speed rating capability.

Most tires today have a service description branded on the wall after the tire size. This service description consists of the following two parts:

The load index is a number usually between 75 and 115. The load index defines the tires load capacity at maximum inflation. The higher the number, the greater the load capacity. The speed symbol is a letter usually between P and Z. The speed symbol defines the speed capability of the tire. In the past, this letter might have been part of the tire size; this continues to be the case with some V and Z rated tires. The higher the letter, the greater the speed capability. Tire companies have charts which define equivalent loads and speed for all load indexes and speed symbols that make up the tire service description.

Refer to the Common Speed Ratings Table in Tire and Wheel Specifications .