2004 Pontiac Bonneville Owner's Manual - Page 339

(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 5-67. (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) Tire Performance Criteria Specification (TPC Spec): 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 car tire size. (A) 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. 5-63