The numbers and letters on tires explain type of tire and the characteristics of its expected performance. This code begins with a P, T, LT, C or ST. The P signifies a passenger car while the T means a temporary tire.
LT is shore for light truck metric, and the C stands for commercial. The ST is a special trailer service tire. After the first letter and before the slash mark, the numbers indicate the width of the tire in millimeters. The numbers following the slash measures the height of the tire as in a percentage with the width.
The second letter indicates the construction of the tire. This is typically an R for radial tires, but might be a D for bias ply construction or B for belted tires. After the second letter, the next set of numbers shows in inches the size of the wheel. The next set of numbers is the tire performance information. The last letter indicates the speed rating of the tire.