Most GM vehicles use P-metric sized tires. P-metric sized tires are available in two load ranges, standard load 242 kPa (35 psi) max and extra load 283 kPa (41 psi) max. Most passenger vehicle tires are standard load.

Most P-metric tire sizes do not have exact corresponding alpha-numeric tire sizes. For example, a P205/75R15 is not exactly equal in size and load carrying capacity to an FR78-15. For this reason, replacement tires should be of the same TPC number (same size, load range, construction) as those originally on the vehicle. If P-metric tires must be replaced with other sizes, a tire dealer should be consulted. Tire companies can best recommend the closest match of alpha-numeric to P-metric sizes within their own tire lines. Refer to Inflation Pressure Conversion Table in Tire and Wheel Specifications .

The metric term for tire inflation pressure is the kilopascal (kPa). Tire pressure may be printed in both kPa and psi. One psi equals 6.9 kPa.