Article: Tires are manufactured with the tire size printed on the sidewall. The sidewall is the outer wall of the tire, rather than the tread that contacts the road. The size should be printed underneath the tire manufacturer name, just above the rim of the tire. For instance, the series may look like this: P 225 / 50 R 17 98 H On some tires, the series of numbers begins with a letter. "P" stands for "P-metric" and denotes a passenger vehicle. "LT" stands for light truck, "T" means temporary spare, and "C" stands for commercial. If you're purchasing a spare or new tire, you'll need to choose the same service type as the rest of the tires. The 3-digit number before the slash denotes the tire width, which is measured from sidewall to sidewall and corresponds to the tread that contacts the road. The measurement is given in millimeters, and all 4 tires must have the same width. For instance, if the first number is 225, the tire tread is 225 mm wide. The numbers after the slash indicate the aspect ratio, which compares the tire's section height with the tire's section width. If you're replacing only 1 tire, make sure it has the same aspect ratio as the others. For example, if there is a "50" after the slash it means the tire's section height is 50% of the tire's section width.

What is a summary?
Find the series of numbers on the sidewall. Recognize that the first letter denotes the service type. Note that the first 3-digit number identifies the tire width. Understand that the following 2-digit number is the aspect ratio.