What do the three sets of numbers on tire size?

Answer 1

Say you have a tire size 205/60HR16:

205 is the section width of the tire in millimeters. Section width is the overall width from sidewall to sidewall. Tread width is typically 90% of the section width. In the above size, the section width is 205mm.

The second number is the aspect ratio. This is the percentage ratio of the sidewall height to section width. In the above example, the sidewall height is 60% of the section width.

The last number is the wheel diameter in inches. So in the above example, the wheel diameter is 16 inches.

The R in the size designation means the tire is a radial tire, as almost all car tires are. The letter in front of the R (H in the above example) is the speed rating of the tire. The speed rating is the maximum speed the manufacturer recommends for the tire.