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How to Measure a Boat Trailer Axle? (w/ Images)

Written by J. Harvey / Fact checked by S. Numbers

how to measure a boat trailer axle

At some point, your boat trailer axle may need replacement due to damage. Knowing how to measure a boat trailer axle is critical to ensure the replacement is accurate.

The critical measures are the hub face, brake flange, spring center, and end-to-end spindle.

This article will provide you with the steps to measure these things accurately. Stick around to learn how to get trailer axle dimensions and see measurement diagrams.

Hub Face Measurement


Note: This image shows an illustration for measuring the hub face, brake flange and spring center.

Measuring trailer axles can be challenging, but there are key things you can measure to ensure that you will purchase the correct replacement. One of the key methods is to measure the hub face.

The hub face is the part where the axle contacts the wheel. Measuring the hub face is one method to measure axle length.

  1. Removing the tires and wheels can make your measurement more convenient. Having another person to help you hold the other side of your tape measure is also better.
  2. To start measuring, hook the measuring tape on the outside of the hub. Then, extend it across the axle to the other side at the same spot.

Brake Flange Measurement


Another part that is critical for trailer axle measurements is the brake flange. This is an alternative method if the axle hub is missing. Measuring the brake flange will allow you to get the hub face measurement.

To begin, hook the tape on the outside of one brake flange and extend it to the outside of the opposite brake flange.

Add the standard flange-to-hub dimension to the result to get the hub face measurement.  The standard distance between brake flanges and hubs depends on the axle’s weight capacity. Axles that can load 3,500 pounds generally have 3″ between the flange and the hub.

Spring Center Measurement


It is critical that this measurement is accurate to avoid damaging the axles.

  • It is best to have another person hold the other end of the tape measure to obtain the correct length from one side of the spring to the opposite side.
  • However, if you can’t get some help, you can hook the measuring tape on the outside of the spring and extend it through the opposite side.

End-to-End Spindle Measurement


Another method to measure an axle on a trailer and determine the correct axle for replacement is to measure trailer axle spindle. Experts say that this method may not be very accurate, but should help in narrowing down your options.

  1. You need to remove the wheels on both sides to do this. Taking the measurement is better with a friend to hold the other side of the tape measure.
  2. However, you can hook the tape measure to the outside of the spindle and measure through the same point on the opposite side.
  3. To get the hub face measurement, you need to subtract 5” if you have a 2,000 and 3,500 pound trailer.

Other Relevant Information and Tips When Measuring a Boat Trailer Axle


  • Know the  type of trailer axle do you have. Do you have a boat trailer torsion axle or a spring? The answer to this question is important for you to be guided properly when looking for a replacement. 
  • Aside from the key measurements discussed above, it is also important to measure axle width. You also need to measure trailer axle diameter.
  • Knowing what size of bearing you need for your axle is also critical. This resource shows a chart for bearings.
  • Trailer axles may also have different specifications. They may differ in suspension type, mounting position, load capacity, hub face distance, etc. Some trailer axles are with brakes, while some are without.
  • Some boat trailer axles may come with hubs, while some may not. Other trailer axles could use drums for the brake.
  • Experts say that there are no standard trailer axle lengths. There are common boat trailer axle sizes, but getting a build-to-order axle is highly recommended. 
  • For torsion axles, you can choose from 44″ to 80″. These different lengths also have different load capacities.
  • The formula for computing your axle length is Chasis Width + (Clearance x 2) + (BackSpace x 2). This trailer axle length formula can be useful in determining the length of your axle.

To further assist you with your axle replacement, I suggest you check the trailer axle size chart here. The chart will provide helpful information about the capacity of the axle depending on its size.


There are ways to determine the length of your boat trailer axle during replacements. The key method is to measure the hub face accurately. If the hub face is unavailable, you can consider measuring the brake flange, spring center, and spindle.

If you are confused about how to measure a boat trailer axle, you can contact any local trailer component store. The professionals at the store should be able to assist you in getting the correct replacement.

Read more: How wide is a boat trailer?

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