What does 225-55R18 mean?

Tire sizes are easy to understand once you learn how to read them.  On this page you'll find a color-coded explanation of the 225-55R18 tire code.

225

This number indicates that your tire has a width of 225 millimeters.

55

This number means that your tire has an aspect ratio of 55%.  In other words, your tire's sidewall height (from the edge of the rim to the tire's tread) is 55% of the width.  In this case, the sidewall height works out to be 123 millimeters.

R

This letter denotes how your tire was constructed.  Radial is the standard construction method for about 99% of all tires sold today.

RRadial
BBias Belt
DDiagonal
18

The tire size was designed to fit rims or wheels that are 18 inches in diameter.