The load range or ply rating branded on a tire's sidewall helps identify its strength and ability to contain air pressure. While specific load ranges are assigned to passenger tires, load ranges are identified in ascending alphabetical order for light truck tires. Common passenger, light truck and special trailer tire load ranges, equivalent ply ratings and load inflation pressures for radial ply tires are shown below:
Before load ranges were embraced, ply ratings were used to identify the strength of light truck tires with higher numerical values assigned to tires featuring heavier duty constructions.
Modern load range/ply ratings do not count the number of ply layers inside the tire. In fact, they indicate an equivalent strength based on early bias ply tires. Light truck tires, even those with heavy duty ratings (10-14 ply rated), actually have two or three fabric body plies, or one steel ply while many radial passenger tires have one or two body plies.