A measure of the strength of tires based upon the strength of a single ply of designated construction. An eight-ply rating does not necessarily mean the tire has eight plies, but rather that the tires has the strength of eight standard plies.

Index of strength of a tire, originally but not any longer the number of plies.

A measure of tire strength based on the strength of a single ply of specified construction. An 8 ply rating does not necessarily mean that the tire has 8 plies but that the tire has the strength of 8 standard plies. Rating can be specified by alpha designator, as Load Range F (PR12).