Why Do Some Trailer Tires have the Letter R in the Size and Others the Letter D

Published 12/07/2015

Question:

What is the difference between the R and D listed on the tires?

asked by: John R

Expert Reply:

The difference between the letters D and R on a trailer tire size is to show the different tire's construction. D stands for bias ply and R for radial.

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.

A bias ply tire has a stiffer sidewall than a radial, a feature that might be useful for off road applications like farm use.

At one time radials were more expensive than bias ply tires, but now they are closer in price. This makes radials a much better value.

expert reply by: Jameson C