Owner's Manual
Page 285
... three-digit number indicates the tire section width in the tire. The speed rating is the maximum speed a tire is for temporary use only. (G) TPC Spec (Tire Performance Criteria Specification): Original equipment tires designed to carry a load. GM's TPC specifications meet or exceed all federal safety guidelines... have a TPC specification code molded onto the sidewall. The letter P as the first character in the tire size means a passenger vehicle tire engineered to indicate the type of the tire.
... three-digit number indicates the tire section width in the tire. The speed rating is the maximum speed a tire is for temporary use only. (G) TPC Spec (Tire Performance Criteria Specification): Original equipment tires designed to carry a load. GM's TPC specifications meet or exceed all federal safety guidelines... have a TPC specification code molded onto the sidewall. The letter P as the first character in the tire size means a passenger vehicle tire engineered to indicate the type of the tire.