If you are in the market for a new set of tires there has never been a better time to learn how to read tire sizes . Fortunately it is based on a standardized system developed by the Department of Transportation so every tire uses the same formula to identify the size and ratings.
The tire size can be located on the sidewall of the tire. If the tire is older and been well worn it may be harder to read but it should still be there. You should see a series of numbers and letters that look something like this: P225/55 R17 95H.
The first letter, P, indicates the type of vehicle the tires are rated for. “P” for passenger, “T” for temporary spare, “LT” for light truck, “C” for commercial, and “ST” for special trailer.
The first set of numbers, 225, represents the width of the tire in millimeters. This is from the widest point of the outer sidewall to the widest point of the inner sidewall when the tire is mounted on the rim.
The second set of numbers, 55, identifies the sidewall aspect ratio. This is the ratio of the sidewall height (tread to rim) compared to the section width. In this case the sidewall height is 55% of the total width.
The second letter, R, refers to the tire’s internal construction. “R” for radial is the most common; however some tires have a diagonal, “D”, construction and some have a belted, “B”, construction.
The third set of numbers, 17, indicates the tire and rim diameter that should be matched together. Most passenger vehicles have a diameter expressed in full inches, sometimes called “inch rims”, while larger trailers and trucks will sometimes have diameters expressed in “half inches”.
The final set, 95H, expresses the recommend load index and speed rating for the tires.