How to Measure a Trailer Axle

Identify Your Axle with These Simple Clues

Whether you need to replace an old trailer axle or you just want the peace of mind of knowing what's under your trailer, there comes a time when you need to identify your axles. And when you're squatting on the ground halfway under your trailer, it can be hard to know exactly what to look for.

If you're lucky, you'll still have a readable sticker on your axle with your weight rating and serial number. However, if this sticker isn't available, you can look at the axle's dimensions to identify it instead. The different measurements work like puzzle pieces, coming together to give you a clear and accurate picture of what size axle you're working with.

Below, we'll show you exactly what to measure, how to measure it, and how to use those measurements to choose the right replacement axle. (We'll even show you what to do if your axle is broken!)

Here are the main measurements that can help you identify your trailer axle and choose the right replacement:

Hub Face Measurement
Spring Center Measurement
End-to-End Spindle Measurement
Axle Tube Diameter

Bonus: Measuring a Broken Trailer Axle

Tip: Don't be shy about removing your trailer's tires and wheels if necessary to get the measurements we talk about below. This can make the process a lot easier!

1. Hub Face Measurement

The hub face measurement (also referred to as the axle track) is one of the most important measurements you’ll need to find when replacing your axle. The hub face (where your axle contacts the wheel and tire) is measured from the outer edge of one hub face to the outer edge of the opposite hub face.

Hub face measurement to outer edge of hub (side one)

Left side - measure to the outside trailer hub face

Hub face measurement to outer edge of hub (side two)

Right side - measure to the outside trailer hub face

Missing your axle hub? Try measuring brake-flange-to-brake-flange instead.

This method isn't quite as accurate as the hub face measurement, but if your axle's hubs are missing, you can use what's called a brake flange measurement instead. Measure from the outside face of one brake flange to the outside face of the opposite brake flange.

Most axles have a standard amount of space between the brake flanges and hubs, depending on the axle size. If you know what capacity your axle is and you know your brake flange measurement, just add the standard flange-to-hub dimension to your brake flange length to obtain your hub face measurement.

So what's the standard distance between brake flanges and hubs? it depends on the axle's weight capacity. For instance, 3,500-lb axles generally have 3" between each flange and hub. So if we add 6" (3" for each side) to our brake flange measurement, we get our hub face number. (See our chart below for the correct number of inches to add to your brake flange measurement.)

Brake Flange to Brake Flange Measurement

Measure to the outside of each brake flange

Using Flange Measurement to Find Hub Face Measurement

2. Spring Center Measurement

The spring center measurement might be the most important to get right. You want to make sure your new axle's springs are located in the same place as the old ones so they don't obstruct the wheels, tires, or other components on your trailer.

While holding your tape measure in the center of your spring, measure to the center of the opposite spring. (You'll use the same method regardless of whether your trailer’s springs are mounted above or below the axle.)

Tip: If you don't have a friend nearby to hold the end of the tape measure, you can still get this measurement solo. By hooking your tape measure on the outside edge of one spring, you can then measure to the inside edge of the other spring. This measurement will be identical to a center-to-center measurement.

Trailer Axle Spring Center Measurement - Left Side

Trailer Axle Spring Center Measurement - Right Side

3. End-to-End Spindle Measurement

With both wheels removed, hook your tape measure on the end of one spindle and run it to the end of the opposite spindle. Then, make sure the new axle you're shopping for has the same end-to-end measurement. This isn't as accurate as measuring for the hub face and spring center, but it can help narrow down your options or double-check that you're selecting the right axle.

Spindle to Spindle Trailer Axle Measurement

Measuring a trailer axle spindle-to-spindle

4. Axle Tube Diameter

When in doubt, you can always double check your axle tube diameter.

Generally speaking, axles of certain capacities have axle tubes of specific diameters. Make sure your new axle has the same tube diameter as your old one.

Other Identifying Axle Features

The measurements above will generally get you to the right axle. But if you need to narrow it down a bit further, there are a few other identifying features and measurements you can look for.

Axle Capacity / Tube Diameter: Choose a new axle with the same capacity as your current axle. You can usually find your capacity on a sticker or stamp on the axle (or sometimes on the trailer itself, if your axles came OEM). If you can't find your capacity this way, you can narrow it down by measuring the tube diameter. Learn more about finding your axle capacity here.

Wheel Bolt/Lug Pattern: Your trailer's wheel bolt pattern is another feature you can use to find the axle you need. Specific bolt patterns are commonly seen on specific axle sizes. Learn how to find your wheel bolt pattern here.

What Does Your Bolt Pattern Say About Your Trailer Axle?

How to Measure a Broken Trailer Axle

If your trailer axle has been through it and is bent or damaged in some way, you may not be able to use the traditional measurements. In this case, here are a few other options.

For Dual-Axle or Triple-Axle Trailers:

If your trailer has more than one axle, you can get the measurements on the remaining good axle(s). Those measurements will be the same as your broken axle’s measurements.

For Single-Axle Trailers:

If you’ve only got one axle to work with, you might still be able to find your hub face measurement, even if your axle doesn't have brake flanges. If your axle has brake flanges, use the brake flange to brake flange measurement we discussed above.

If your axle doesn't have brake flanges, and one of your hubs is missing or your axle is broken from the outer edge of the leaf spring, you can use the method below to find your measurement. (You cannot use this method if your axle has broken anywhere between the two leaf springs. This will prevent you from measuring accurately, leading to an incorrect hub face measurement.)

Measure the distance from the center of one leaf spring to the outside edge of the hub face (measurement A)
Double the value
Add the value to your spring center measurement

This new value should be equivalent to your hub face measurement.

How to Measure for a Broken Trailer Axle Diagram

Example:

Measurement A = 7.5"

Measurement B = 74"

(7.5 * 2) = 15

15 + 74 = 89

Hub Face Measurement = 89"

About Eric H.

Everything vehicle related, I want to know about it. I always enjoy learning new things, and here at etrailer, we are never short on learning opportunities. I know you're not supposed to take your work home with you, but I do. There is something very special about having your hobbies and career coincide with one another.

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