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Trailer Tire Size Guide

Posted by Pete's Tire Barns on 2/9/2012 to Trailer

Trailer Tire Size Guide

Reading a Trailer Tire

Reading a Trailer Tire

Trailer tire sizes are broken into main groups 12 inch and smaller and 13 inch and larger. Sizes 12 inch and smaller are generally listed by a two number size, such as 4.80-8 or 5.70-12. The first number in this size is the width of the tread, the second number is the size of the rim that it mounts on. Large size trailer tires are made up of three numbers. For example, a common trailer tire size is ST225/75R15.  ST stands for special trailer and indicates that this tire is designed to be used on a trailer. 225 is the width of the tread in millimeters. 75 is the height of the sidewall represented as a percentage of the tread width. 15 is the size of the rim this tire mounts on. In the case of a 225/75R15, the tire is roughly 9 inches wide, 28 inches tall and mounts on a 15 inch rim.

Trailer Tire Size Conversion Guide

Old Size Current Size
B78-13ST ST175/80R13
C78-13ST ST185/80R13
F78-14ST ST205/75R14
G78-14ST ST215/75R14
F78-15ST ST205/75R15
H78-15ST ST225/75R15


Load Range Ply Pressure
B 4 35 psi
C 6 50 psi
D 8 65 psi

Need more information, try one of our other informative trailer tire articles:

How to Measure your Trailer Wheels Bolt Pattern

Bias Trailer Tire versus Radial Trailer Tires

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