What do the Numbers and Letters on Trailer Tires Mean?

What do the Numbers and Letters on Trailer Tires Mean?

The Tire and Rim Association, Inc. has established interchangeable standards for tires, rims, the associated parts for the guidance of the tire, and rim manufacturing industry. This set of uniform standards helps you, the consumer, be confident when buying new rims and tires for your trailer. Below we have provided illustrations and will outline what the trailer tire sidewall markings mean so you know which new trailer tires to buy.

  1. In this example, let’s say we have a trailer tire labeled ST175/80D13C.


  1. The “ST” indicates that these are tires specifically for trailer use. The ST stands for “Specialty Tires.” ST tires should never be used on anything other than trailers.
  2. After the ST, we see the number 175. This means the maximum width of the trailer tire is approximately 175 millimeters at its widest point.
    1. After the “/” we see the number 80. This indicates the height of the sidewall on the tire is 80 percent of the width.


  1. The letter “D” after the 80 shows that this is a bias ply tire as opposed to a radial (R). Bias tires have their plies running diagonal from one bead to the other bead at about a 30 degree angle.

Degree Angle

  1. The second to last character is a “13” and indicates the rim that the tire will fit on. This tire will fit on a 13 inch diameter rim.

Tire Diameter

  1. Finally, the letter “C” indicates the load range of the tire.

Buy Trailer Tires Today

Now that you know what the numbers on your trailer tires mean you can confidently buy them. Buying your trailer tires online from us allows you to save money, time and gives you the peace of mind that you are getting the best prices in the industry.

Contact us today for more help on buying tires for your trailer.