Trailer Wheels and Tires Technical Definitions Guide

Posted by Petra on 3/11/2013 to Trailer Tires FAQ

You may not think of your trailer wheels as being particularly specialized, but there are actually many specific measurements that must be just right. The wheel's size ensures that it flows smoothly with the others and that the cargo you are carrying on the trailer has a smooth, safe ride to your destination. When you're measuring your trailer wheel, you need to pay attention to several specific dimensions.

  • The wheel centerline is the exact center of the wheel, measured from front to back. The trailer tire needs to be balanced around the centerline for proper operation.

  • The wheel diameter is the distance across the trailer wheel at its longest, measured at the spots where the tire seals with the wheel.

  • The bolt diameter is the distance across the bolt hole where you will secure the wheel to the trailer.

  • The mounting pad is the part of the wheel in the center that touches the face of the hub on your trailer.

  • The drum side is the side of the wheel that faces your trailer and drum.

  • The street side is the side of the trailer wheel that faces the street.

  • The backspace is the distance between the mounting pad and the edge of the trailer wheel on the drum side.

  • The wheel offset is the space between the centerline of your trailer wheel and the mounting pad.

Depending on your trailer wheel's configuration, the wheel offset may be zero, positive or negative. It's very important to understand the difference between these because they affect how the weight of your trailer is distributed over your wheels.

Here's a brief description of each option:

  • Zero offset is when the mounting pad is exactly at the wheel centerline (this is the most common offset with Trailer Wheels).

  • Positive offset is when the mounting pad is closer to the street side than the drum side.

  • Negative offset is when the mounting pad is closer to the drum side than the street side.

Being able to understand and measure each of these components is very important. You'll need the information to choose the proper trailer wheels when it's time to replace them.