Tire codes use a standardized system of numbers and letters to specify the type of tire, its size, how much weight it can carry, how it was made and its speed rating. Tires are also stamped with their tread patterns and dates of manufacture.
The first part of a tire code begins with one or two letters that indicate the type of tire it is. "P" indicates a passenger car tire, "LT" indicates a light truck tire, and "T" means the tire is for temporary use only.
The three numbers that follow indicate the tire's nominal or section size. This is a measurement from one of the tire's sidewalls to the other. It is followed by a slash and two more numbers that describe the tire's aspect ratio. A tire's aspect ratio is the height of each of its sidewalls.
Following the aspect ratio is another letter that indicates the construction methodology used in the tire. "R" indicates a radial tire, "D" a diagonal tire and "B" a tire with a bias belt. The number following the construction letter shows the tire's diameter in inches.
A space usually follows the diameter, after which the code shows the tire's load index, a number that describes how much weight the tire can carry. The final part of the code describes the vehicle's speed rating.