Learn How to Measure the Trailer Axle on a Flatbed Trailer

How to Measure a Flatbed Trailer Axle the Right Way

If you have ever stood in front of a parts counter trying to order a replacement axle, you already know how unforgiving the wrong number can be. Trailer axles are not one-size-fits-all, and a measurement that is even half an inch off can mean a part that does not fit, an extra trip to the supplier, and a flatbed sitting on jack stands while a job sits on hold. Whether you are repairing your own trailer or prepping to relist a flatbed on a peer-to-peer rental marketplace, getting these measurements right is fundamental.

This guide walks through every measurement you need to take when sizing or replacing a flatbed trailer axle, with pro tips for accuracy and a quick reference table you can use at the parts counter.

Why Accurate Axle Measurements Matter

Axle dimensions affect three things: fitment, capacity, and ride quality. The wrong hub face length can throw off wheel alignment. The wrong spring center can prevent the axle from bolting into your suspension. The wrong spindle diameter means none of your bearings will seat. Measure once on paper, twice in person, and you save hours and dollars.

Tools You Need Before You Measure

Gather a 25-foot tape measure, a steel ruler with imperial and metric markings, a pen and notebook, a flashlight, jack stands, and a torque wrench if you plan to remove the wheels. A second set of hands also helps when you are checking long measurements like hub face to hub face on a tandem trailer.

The Six Measurements to Take

Every flatbed axle replacement needs the same set of dimensions. Take them in this order to avoid forgetting one.

1. Hub Face to Hub Face

This is the total length of the axle, measured from the outer face of one hub to the outer face of the other. Stretch the tape measure straight across, parallel to the ground, with both wheels pointed straight ahead. Most trailer axles fall between 71 and 95 inches hub face to hub face, with 89 inches being one of the most common sizes for tandem flatbeds.

2. Spring Center to Spring Center

Measure the distance between the centers of the two spring perches welded to the axle. This is what determines whether the axle will bolt into your existing suspension. Common spring center distances are 71, 74, and 84 inches, depending on trailer width.

3. Axle Tube Diameter

Wrap your tape around the bare axle tube and divide by pi to get the diameter, or use a caliper if you have one. Standard tube diameters are 1.75, 2.375, 3.0, and 3.5 inches. Heavier-rated axles use larger tubes to handle the load.

4. Spindle Type and Bearing Numbers

Pop a wheel off and look at the spindle. The bearings will have part numbers stamped on the inner race, like L44649 (inner) and L68149 (outer). Match these numbers exactly when you order replacement bearings. The spindle taper also tells you the axle's load class.

5. Bolt Pattern

Count the lug bolts and measure the bolt circle diameter. Common bolt patterns include 5 on 4.5, 6 on 5.5, and 8 on 6.5. Get this measurement wrong and your existing wheels will not fit the new axle.

6. Brake Type and Drum Size

Note whether the axle has electric brakes, hydraulic brakes, or no brakes. Measure the brake drum diameter (typical sizes: 7, 10, and 12 inches). The brake size confirms axle capacity and tells the supplier which brake assembly your trailer uses.

Quick Reference Measurement Sheet

Use this table at the parts counter to confirm every dimension you collected before placing an order.

Typical Hub Face to Hub Face Lengths

The chart below shows the most common axle lengths sold for flatbed trailer applications.

NeighborsTrailer.com

Pro Tips for Accuracy

Measure on level ground with the trailer unloaded so the suspension sits at its natural ride height. Take each measurement twice and write it down both times. If the numbers do not match, take a third reading. For long measurements like hub face to hub face, run the tape just under the axle, not over the springs, to keep it level. Photograph the spindle, brake assembly, and bearing numbers for a parts catalog reference later.

For owners getting their flatbeds road-ready in the spring, run through the trailer axle alignment guide after replacing an axle. Before any new haul, the leaf spring vs torsion axle suspension guide can help you understand how your suspension setup affects measurement choices.

When to Replace vs Rebuild

Bent axles, cracked welds, and worn spindles call for full replacement. If only the bearings, brakes, or seals are worn, you can rebuild instead and save several hundred dollars. Inspect the axle tube with a straightedge to confirm it is not bowed, then decide which path makes sense.

Frequently Asked Questions

What is the difference between hub face and hub flange measurements?

The hub face is the very outermost surface of the wheel hub, which is what you measure across when sizing an axle. The hub flange refers to the mounting surface where the wheel bolts on. Manufacturers use hub face length as the standard axle length specification.

Can I install a longer axle than the original?

You can, but only if your trailer fenders, wheel wells, and bolt patterns accommodate the wider stance. Always check with the trailer manufacturer or a qualified shop before changing axle dimensions.

How do I know if my axle is bent?

Roll the trailer slowly and look for tire wobble. Set a straightedge along the axle tube and check for gaps. Uneven tire wear after only a few hundred miles is another classic sign of a bent axle.

Are torsion axles measured the same way?

Mostly. Hub face and bolt pattern measurements stay the same, but torsion axles use a mounting bracket spacing instead of spring centers. Note the bracket-to-bracket dimension when ordering a torsion replacement.

Conclusion

Measuring a flatbed trailer axle the right way protects your investment, your cargo, and your schedule. Take the six measurements in order, double-check each one, and you will be ready to order the exact replacement parts on the first try. When the trailer is back together, you can confidently rent it out on Neighbors Trailer and put it back to work.

Related Articles

• The Importance of Trailer Axle Alignment
• Leaf Spring vs Torsion Axle Suspension Systems
• Flatbed Trailer Tire Bolt Guide
• Trailer Towing Capacity Explained

Content updated May 2026