What does 275-40R20 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 275-40R20 tire code.

275

This number indicates that your tire has a width of 275 millimeters.

40

This number means that your tire has an aspect ratio of 40%.  In other words, your tire's sidewall height (from the edge of the rim to the tire's tread) is 40% of the width.  In this case, the sidewall height works out to be 110 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
20

The tire size was designed to fit rims or wheels that are 20 inches in diameter.