How to Measure Trailer Leaf Springs
Why Correct Measurement Matters
Leaf springs are a primary structural component of a trailer’s suspension system. They support the trailer’s load, control axle position, and maintain proper ride height. Selecting the wrong spring can result in poor handling, uneven tire wear, axle misalignment, and reduced braking effectiveness.
Leaf springs are not measured universally. Measurement depends on spring end style, and incorrect measurement is one of the most common causes of replacement fitment issues.
What You Should Know Before Measuring
- Leaf springs must be measured unloaded
- Free length is not the same as installed length
- Different spring styles require different measurement points
- Spring width, leaf count, and capacity must also match
Common Trailer Leaf Spring Types
-
Double Eye Leaf Springs
Eyes on both ends, typically used with shackles on both mounting points. -
Open Eye Leaf Springs
One rolled (open) eye and one slipper-style end. -
Slipper / Hook / Flat / Radius End Springs
No rear eye. The rear of the spring slides or rests in a hanger.
Measurement Reference
| Spring Type | How to Measure | Key Dimensions |
|---|---|---|
| Double Eye | Measure from mounting point center to mounting point center | A = Free Length |
| Open Eye | Measure from mounting point to the furthest inside point of the open eye | A = Free Length B = Arch Height |
| Slipper / Hook / Flat / Radius | Measure from the front mounting bolt to the end of the spring | A = Free Length |
Leaf Spring Measurement Diagram
The diagram below illustrates proper measurement points for each leaf spring type. Dimension A represents free length. For open eye springs, B represents arch height.
Where Measurement Errors Commonly Occur
- Measuring eye-to-eye on slipper springs
- Measuring overall length instead of free length
- Ignoring arch height on open eye springs
- Replacing a single spring on a multi-axle trailer
- Assuming capacity alone determines compatibility
Who This Guide Applies To
This guide applies to most utility trailers, equipment trailers, dump trailers, and similar towable applications using leaf spring suspension systems. It is intended for trailer owners, technicians, and fleet operators performing maintenance or component replacement.
When Leaf Springs Should Be Replaced
- Visible cracks or broken leaves
- Uneven ride height side to side
- Axle contacting frame or bump stops
- Persistent tire wear after alignment
- Noticeable sag compared to original ride height
Accurate leaf spring measurement is the foundation of proper suspension repair. When measurements are uncertain or multiple spring styles appear similar, verify specifications before ordering to ensure correct fit, alignment, and long-term suspension performance.
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