Decoding Metric Trailer Tire Sizes

This post was written by ghoj on January 27, 2015
Posted Under: Trailer Tires & Wheels

For someone who might not be familiar with the numbers and letters on a TRAILER TIRE, replacing one could prove frustrating. We will break down the metric size designation found on most trailer tires so that identifying your needs should be simple.  For an example we will be identifying the meaning of the numbers and letters on a


ST stands for “Special Trailer” and signifies its use for trailers only.

205 is the “Section Width” of the tire in millimeters when mounted on the specified rim and inflated to the maximum pressure. The Section Width is the measurement of the overall width of the tire not including any protruding letters or protective ribs around the outer sidewall. To convert this to inches simply divide the number by 25.4
205 divided by 25.4 = 8.07″

75 is the aspect ratio of section height to section width. Also known as the series number or profile of the tire, this number means that the height of the tire is 75% of the width. So since we know that the Section Width is 8.07″ then that means 75% of 8.07 is the section height. (8.07 x .75 = 6.05″)

R designates the tire as a Radial Ply as appose to a Bias Ply (D Designation). For a more technical look at the difference check this out.

14 is the rim size.  This is the diameter of the rim measured in inches from bead to bead.  The actual physical diameter will measure slightly larger then the listed size because the beads are inside the lip of the rim.

Another number set that you will find on a tire is the Birthday.  This will be represented by a 4 digit number inside of an oval. The first two digits are the Week # and the second two digits are the Year.  0214 Would mean they were manufactured in the 2nd week of 2014.

We hope this was helpful in identifying what the numbers and letters mean on your trailer tire.  Remember to always run your trailer tires at maximum PSI filled when cold.  To check out our full list of tires and more Tech info visit us at

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