Difference Between Trailer Tire Size that Has a Letter D and Letter R

Updated 10/21/2015 | Published 10/20/2015

Question:

I went to Walmart to buy a tire for my trailer. My trailer tires are ST205 75D15 and they put me a ST205 75R15. Does it matter?

asked by: Roel

Expert Reply:

The difference between the two trailer tire sizes is that the letter D in the first size you listed ST205/75D15 stands for bias ply and the letter R in the tire size that they put on your vehicle stands for radial.

Radial tires are preferred over bias ply, but if the rest of your tires are bias ply and now you have a single radial you would want to strongly consider having all tires match.

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.

I attached a link to a page that has all of the 205/75-15 tires we offer. You will be able to select radial or bias ply from the filters depending on which style you prefer.

expert reply by: Jameson C