Pontiac G8 manual Tire Size

9-42 Vehicle Service and Care

(E)Tire Inflation: The temporary use tire or compact spare tire should be inflated to 60 psi (420 kPa). For more information on tire pressure and inflation see Inflation - Tire Pressure on page 9-46.

(F)Tire Size : A combination of letters and numbers define a tire’s width, height, aspect ratio, construction type, and service description. The letter T as

the first character in the tire size means the tire is for temporary use only.

(G)TPC Spec (Tire Performance Criteria Specification): Original equipment tires designed to GM’s specific tire performance criteria have a TPC specification code molded onto the sidewall. GM’s TPC specifications

meet or exceed all federal safety guidelines.

Tire Size

The following illustration shows an example of a typical passenger vehicle 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 60, as shown in item C of the illustration, it would mean that the tire’s sidewall is 60 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 range and speed rating of the tire. The load index represents the load carry capacity a tire is certified to carry. The load index can range from 1 to 279. The speed rating is the maximum speed a tire is certified to carry a load. Speed ratings range from A to Z.