How to Accurately Measure Trailer Leaf Springs

Written by: Beth B

Updated on: 7/25/2024

Est. time to read: 5 mins

Measuring trailer leaf springs requires facing the raw underbelly of your trailer, a dark place you may have never had the pleasure of exploring until now. Fortunately, it’s a surprisingly simple bit of maintenance, and also the first step in replacing leaf springs when you find they are seriously corroded, sagging, or have cracks in the leaves. To learn how to find the right springs for your trailer, read on.

Before you start measuring, it will be necessary to jack up your trailer using jack stands: this will allow the axle to hang freely. It is also necessary to measure your trailer while it is unloaded, as the weight of the load may cause inaccurate measurements.

It’s also a good idea to acquaint yourself with each part of the springs so you’ll know what you’re looking at.

Note: Leaf springs should always be installed in pairs so you ensure you are using the same springs on each side of the axle. This will also ensure they ride and wear the same way on each side.

Parts of a Trailer Leaf Spring

Center Pin

The center pin slides into the middle of the leaf spring and holds the leaves together.

Eyes/Slippers

The loops or tails at the end of the springs that attach to the axle with bolts or shackles to keep it in place.

Springs/Leaves

The individual leaves sit over or under the axle and provide a smoother ride by absorbing bumps in the road. They support the weight of your trailer.

How to Measure Leaf Springs

Measuring Leaf Spring Flat Length

The flat length method will help you obtain a measurement that reflects the length of the springs if they were flat instead of curved. This method is the most accurate way to measure leaf springs because it will work no matter how worn your springs have become over time.

A soft tape - or tailor’s measuring tape - may come in handy for easier measuring along the springs’ curve.

For double-eye leaf springs, measurements are usually taken from the middle of the center bolt to the middle of one eye (the measurement should be the same from either side of the bolt).

For slipper springs, you’ll need to measure from the middle of the center bolt to the middle of the eye, then from the middle of the center bolt to the tip of the slipper.

Flat Length Diagram for Double Eye Springs

Measuring Flat Length for Double-Eye Springs

Measuring Flat Length for Slipper Springs

Measuring Eye-to-Eye / Eye-to-Slipper

While the flat length method works regardless of how flat your springs have become from time or use, this second approach is faster than the flat length method and still produces results that will help you obtain the correct springs. (It can also easily be done with a traditional tape measure.)

The Eye-to-Eye Method

The eye-to-eye method is as straightforward as it sounds.

All it entails is measuring from the center of one eye straight across the spring to the center of the other eye for the final result.

The Eye-to-Slipper Method

The eye-to-slipper method is similar to eye-to-eye: begin at the center of the eye and measure straight across the spring to the tip of the slipper for your final measurement.

Measuring Leaf Spring Width

Sometimes you might also want to get a measurement of your springs’ width. Simply measure across the top of the top leaf to obtain this measurement. (For reference, most trailer springs measure out from 1-¾ to 2 inches wide.)

Measuring Leaf Spring Height

The height of the spring can be found simply by measuring from the middle of the center pin straight up to the top of the eye/slipper. You can alternatively place the leaf spring upside down on a flat surface and measure from the floor up to the center pin for an easier experience.

Where to Go from Here

The final component you will need before selecting the right leaf springs for your trailer is your axle capacity. If you’re unsure of your axle capacity, you can reference the manufacturer’s sticker/plate located on your trailer or check out our article, How to Tell the Weight Rating of a Trailer Axle.

Armed with your axle capacity and measurements, you're now ready to purchase your new leaf springs, which can be found here.

In no time, your trailer will have the support it needs to haul your heavy loads, whether you’re traveling across town or lugging cargo over rugged terrain. Wherever you decide to go, you and your springs will be prepared for the adventure.

About Beth B.

When I explain my position at etrailer to the folks back at home, I usually preface with, “Writing is about 15% of my job. The other 85% is research, hands-on product testing, and putting myself in the shoes of our customers (whom we call neighbors).” At etrailer, I have the opportunity to explore the products I write about in person every day, a privilege many writers don’t have. On a Tuesday morning, for instance, you may find me outside of a 5th wheel collecting pictures of its scissor jacks for an article. On Wednesday, I might switch gears to measure leaf springs in our warehouse, while Thursday is when I’ll finally get behind the keyboard (that is, in between driving off-site to film how-to videos with the team). If you have a question, it’s my mission to not only provide you with an answer, but to equip you with the knowledge and resources you need to face real-world challenges like a pro.

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