What Does the R Stand for In a Trailer Tire Size

Published 06/18/2015

Question:

ST20575R15 What does the R stand for?

asked by: Chris K

Expert Reply:

The R in the ST20575R15 stands for radial which is the way the tire is constructed. The main difference between a radial ply and a bias ply tire is how the tire is constructed. The cords inside a bias ply tire run at a 32 degree angle to the direction of travel, and the cords on a radial tire run at a 90 degree angle to the direction of travel, or across the tire from wheel lip to wheel lip.

A radial tire flexes more than a bias tire, giving it better ground contact, traction, stability, and tread wear.

A radial tire will normally run cooler than a bias ply tire, especially when the tire is under a load. A tire that runs cooler will last longer.

expert reply by: Jameson C