GMC Sierra Owners Manual
Tire DesignationsVehicle Care / Wheels and Tires / Tire Designations
Tire Size
The examples show a typical passenger vehicle and light truck tire size.
(A) Passenger (P-Metric) Tire:
The United States version of a metric tire sizing system. The letter P as the first character in the tire size means a passenger vehicle tire engineered to standards set by the U.S. Tire and Rim Association.
(B) Tire Width: The three-digit number indicates the tire section width in millimeters from sidewall to sidewall.
(C) Aspect Ratio: A two-digit number that indicates the tire height-to-width measurements.
For example, if the tire size aspect ratio is 75, as shown in item C of the tire illustration, it would mean that the tire's sidewall is 75 percent as high as it is wide.
(D) Construction Code: A letter code is used to indicate the type of ply construction in the tire. The letter R means radial ply construction; the letter D means diagonal or bias ply construction; and the letter B means belted-bias ply construction.
(E) Rim Diameter: Diameter of the wheel in inches.
(F) Service Description: These characters represent the load index and speed rating of the tire. The load index represents the load carrying capacity a tire is certified to carry. The speed rating is the maximum speed a tire is certified to carry a load.
(A) Light Truck (LT-Metric) Tire: The United States version of a metric tire sizing system.
The letters LT as the first two characters in the tire size mean a light truck tire engineered to standards set by the U.S. Tire and Rim Association.
(B) Tire Width: The three-digit number indicates the tire section width in millimeters from sidewall to sidewall.
(C) Aspect Ratio: A two-digit number that indicates the tire height-to-width measurements.
For example, if the tire size aspect ratio is 75, as shown in item C of the light truck (LT-Metric) tire illustration, it would mean that the tire's sidewall is 75 percent as high as it is wide.
(D) Construction Code: A letter code is used to indicate the type of ply construction in the tire. The letter R means radial ply construction; the letter D means diagonal or bias ply construction; and the letter B means belted-bias ply construction.
(E) Rim Diameter: Diameter of the wheel in inches.
(F) Load Range : Load Range.
(G) Service Description: The service description indicates the load index and speed rating of a tire. If two numbers are given as in the example, 120/116, then this represents the load index for single versus dual wheel usage (single/dual). The speed rating is the maximum speed a tire is certified to carry a load.
