How to Select the Right Trailer Axle

Selecting the best trailer axle for your setup starts with identifying the correct axle capacity and measurements for your trailer. Most trailer owners can find this information on the manufacturer tag located on the trailer frame or tongue. If the tag is missing, measuring the hub face and spring center distances will help ensure the replacement axle fits correctly and supports the trailer’s load. Choosing the proper axle ensures safe towing, proper weight distribution, and long-term trailer performance. This guide explains how to identify the correct trailer axle using manufacturer tags, key measurements, and trailer specifications.

There are numerous things to consider when purchasing a replacement axle for your utility trailer or RV. Do you know the weight capacity of the trailer? Do you know how to measure for a replacement trailer axle and the different styles and orientations you can choose from? Are you in need of new hangers or leaf springs for the axle beam? Choosing the right axle can seem like a daunting task, but after reading the helpful tips outlined in this post, you will be able to purchase your trailer axle with confidence.

• Trailer axle basics
• How to measure a trailer axle
• Trailer axle capacity
• Axle styles & orientation
• Axle FAQs

The main parts of a trailer axle include the axle beam, leaf springs, U-bolts, shackles, and equalizers. These components work together to support the trailer’s weight, absorb road shock, and connect the axle to the suspension system. To start, understanding the parts of a cargo trailer axle will help you during the buying process. Refer to the following diagram and definitions when purchasing axles and axle components.

• Axle beam: A rigid piece of steel that connects a set of wheels; the foundation of your trailer suspension system
• Lugs: The nuts that are used in conjunction with bolts to secure the wheel to the trailer axle
• Attaching parts: Used to bolt leaf springs to onto the hangers
• Hangers: Used to mount the leaf springs onto the trailer
• Leaf springs: Made of several layers of metal that are curved upward and clamped together to form an integral part of the trailer’s suspension system by helping to support the weight
• U-bolts: Used to keep the leaf springs on a trailer’s suspension system together
• Shackles: Allow the leaf spring to change lengths as the trailer travels over different types of terrain
• Equalizers: Connect to the leaf springs; they rock to absorb road shock and smooth out your ride

When people think about trailer axles, they often picture just the axle beam and hubs. In reality, a trailer axle is a complete assembly made up of multiple critical components working together — like spindles, brakes, springs, bearings, and mounting hardware. Understanding the full axle system is key to choosing the right setup for safe towing, proper load support, and long-term performance.

To measure a trailer axle, first check the trailer manufacturer tag for axle specifications and weight capacity. If the tag is missing, measure the hub face distance between the wheel mounting surfaces and the spring center distance between the leaf spring mounts.

Knowing your axle measurements and understanding the different spring axle options will help you choose the right fit for your utility trailer. The easiest place to find the right replacement axle for your trailer is on the tag from the trailer manufacturer that can be found on the tongue or neck of the trailer. This tag should have the VIN number of the trailer and will also include weight capacities needed to make a replacement axle purchase. The axle itself should also have a tag that indicates all the necessary replacement purchase information.

If you didn’t purchase your trailer from a company or can’t find the tag, there are a few other ways to correctly measure for your axle replacement, which we've detailed below.

Whether you have a single-axle, double-axle, or tri-axle trailer, each requires precise measurements to guarantee a smooth and safe ride. In the following videos, we break down the process for each type of application, guiding you step-by-step through measuring. These videos will help you confidently gather the necessary measurements to find the perfect fit for your trailer's axles.

To measure a single-axle trailer, record the hub face measurement and the spring center measurement on the existing axle. The hub face determines wheel spacing, while the spring center ensures the axle aligns with the suspension mounting points.

When measuring a double-axle trailer, measure each axle’s hub face and spring center distances individually. Both axles must match the trailer’s suspension mounting points and spacing between axles.

To measure a tri-axle trailer, measure the hub face and spring center distances for each axle and confirm the spacing between all three axles.

The hub face is the distance from the outside of one hub to the outside of the hub on the opposite side of the axle. Spring center is measured from the center of the spring seat on one side of axle to the center of the spring seat on the other side of the axle. Axle lengths are notated using the hub face distance, a forward slash and the spring center distance. For example, an axle with a 58-inch hub face distance and a 46-inch spring center would be written as 58/46.

The number of bolts or lugs per wheel and the diameter of the circle the bolts are arranged in make up a trailer wheel hub bolt pattern. To measure a 5-lug bolt pattern, pick a bolt and measure from the outside of the bolt. Then, skip a bolt and measure to the center of the next bolt. To measure a 4, 6 or 8-lug bolt pattern, measure center to center of two bolts directly across from one another. The bolt pattern is notated by the number of bolts on a wheel and the diameter of the circle they form. For example, a wheel with 5 bolt holes that forms a circle with a 4.5-inch diameter would have a 5 on 4.5" bolt pattern.

Trailer axle capacity refers to the maximum weight an axle is designed to support. To select the correct axle capacity, match the axle rating to the trailer’s Gross Vehicle Weight Rating (GVWR) and intended load.

Knowing your trailer weight capacity helps you understand your towing limitations. A single axle is just that — an axle with one set of wheels. A tandem axle has two sets of wheels and is basically two single axles put together, assuming the capacities are the same on each axle.

There are a handful of standard axle capacities, ranging from 2,000 pounds up to 10,000 pounds and making it easier to find the right one to replace your existing axle. Here are some of the most common trailer axle capacities:

Refer to the trailer axle capacity chart below or download the printable PDF to see the different weight capacities between spring axles.

The most common trailer axle types are leaf spring axles and torsion axles. Leaf spring axles use metal springs and suspension hardware to absorb road shock, while torsion axles use rubber cords inside the axle tube to provide independent wheel movement and smoother ride performance.

On the above trailer weight capacity chart, you may have noticed a few other axle options that are available, including spindle style, spring orientation and hub style. These are all a part of the buying decision, so we’ve defined each option below.

Spindles provide a surface for your wheel bearings and wheel hub to rotate around. A straight axle has a completely straight design, while a drop axle makes the wheel hub higher than the axle tube, allowing the trailer to sit lower to the ground.

Overslung and underslung describe the ways in which the trailer leaf springs attach to the axle beam. Overslung leaf springs sit on top, or “over” the axle, while underslung leaf springs sit beneath, or “under” the axle. Trailer height, clearance from the axle to the frame and driving stability are all affected by overslung versus underslung leaf springs.

A brake hub allows for electric, hydraulic drum or disc brakes, while an idler hub has no provision for trailer brakes.

Spring axles include the purchase of an axle beam and can be configured with leaf spring, hanger and attaching parts kits.

Leaf spring kits come with leaf springs and U-bolts, but not the hardware to mount the springs onto the trailer frame.

AP suspension kits help you bolt the axle leaf springs to your hangers.

A hanger kit is used to mount the leaf springs on the trailer, but it doesn't include the attaching parts.  

Now that you know the various considerations you should keep in mind while selecting your replacement axle, you should be able to buy with confidence! At Lippert, we build a full line of reliable 2-12K spring axles to meet unique specifications for a wide range of utility trailers, including open and closed cargo, teardrop and travel trailers.