Passenger Tire Service Description

Most tires today have a service description branded on the sidewall after the tire size. This service description consists of two parts: The load index and the speed symbol. The load index is a number usually between 75 and 115, which defines the tire's load capacity at maximum inflation. Higher numbers mean greater load capacity.

The speed symbol is a letter usually between P and Z. which defines 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 speeds for all load indexes and speed symbols that make up the tire service description.