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What Are Overslung and Underslung Springs?
Overslung springs are mounted on top of the axle. The spring’s arch sits above the axle, which raises the chassis higher off the ground.
Underslung springs are mounted beneath the axle. This lowers the trailer’s deck height, bringing the load closer to the ground and making loading easier.
Both configurations use the same core components (leaf springs, U‑bolts, hangers and slippers), but the mounting position changes ride height, handling and suitability for different jobs.
Benefits of Overslung Springs
Increased ground clearance
A higher chassis helps avoid scraping on rutted tracks, farm entrances and work sites.
Better for heavier loads
Additional suspension travel under load can improve control and reduce bottoming out.
Improved tyre and guard clearance
Extra room between tyres, guards and chassis components reduces rubbing risks.
If your trailer regularly carries machinery or operates off‑road, an overslung setup is often the safer, more durable choice.
Benefits of Underslung Springs
Lower deck height
Bringing the load closer to the ground makes ramps easier and loading safer.
Stable towing for certain builds
A lower centre of gravity can help reduce sway at highway speeds.
Gentler approach angles
Ideal for car transporters, low loaders and trailers that need frequent loading and unloading.
Key Factors to Consider When Choosing
Load capacity
Match your spring kit to the trailer’s GVM. Avoid over specifying, which can create a harsh, skittish ride when lightly loaded.
Application
Flat deck, tipper, boat or specialist builds have different ground‑clearance and loading needs.
Road and terrain
Rough or off‑road conditions typically favour overslung. Sealed urban routes often suit underslung.
Clearance and height
Measure guard, fender and tyre clearance before changing configurations to avoid interference.
Common Mistakes When Switching Setups
Incorrect U‑bolt length
Changing the mounting position usually requires different U‑bolt lengths and plates.
Overlooking brake lines and wiring
Re‑route and secure lines to prevent chafing once ride height changes.
Choosing springs that are too stiff
Overspec springs can worsen handling and reduce traction when unladen.
Where to Buy Overslung & Underslung Spring Kits
Explore our full range of trailer spring sets engineered for New Zealand conditions.
Build the right setup with single axle spring kits, tandem axle kits and tri‑axle kits, plus suspension hardware and accessories to finish the job.
Not sure which way to go? Start with our range of leaf springs and match the rating to your GVM and terrain.