View Here : Tire Size Meaning
A system developed by the Department of Transportation, which helps consumers compare and rate tires on tread wear, traction, and temperature. Example: a tire with a UTQG of 400 AB. The 400 is tread wear which represents the tire's comparative wear when measured against the governments mandated tire, which is rated at 100.
Tire Width is the is the width of the tire, measured in inches, when the tire is mounted and inflated to the recommended pressure. Rim Size is the outside diameter of the rim, also called the wheel size, same as in the metric size.