Determining an Axle's Capacity

Published 09/14/2019

Question:

You said to measure the diameter of the axle. Now is that the outside tube we see or pulling the axle out to measure it?

asked by: Eric M

Helpful Expert Reply:

One of the many ways of determining the axle's capacity is to measure the diameter of the axle tube or beam (not the spindle that the hub slips onto). A trailer axle will consist of a tube which is basically a hollow pipe with the spindles welded into or onto the ends.

1,000-lb - 2,000-lb Axle are usually 1-1/2" - 1-3/4" diameter
3,500-lb Axles: 2-3/8" diameter, can also have a 3-1/2" diameter, but rarely
6,000-lb - 7,200-lb Axles: 3" diameter
8,000-lb Axles: 3-1/2" diameter
9,000-lb Axles: 4" diameter
10,000-lb Or more axles: 5" diameter

For example, the # 7461121 axle has an axle tube that's 3 inches in diameter, and it's a 6K axle.

Most folks don't have a caliper large enough to measure an axle beam, so you can get a piece of string and wrap it around the axle and mark the string where the ends meet. Measure that distance and divide it by 3.14 which will give you the diameter.

We can also usually determine the axle capacity from the reference numbers on the inner and outer wheel bearings and the wheel bolt pattern.

If you need further assistance in finding your axle's capacity, just reply with the bearing numbers and the wheel bolt patterns and I'd be happy to help figure it out for you.