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Can Caravan Overlay Axles be inverted?

by | Jul 20, 2017 | Axles | 0 comments

Can I invert my Caravans Overlay Axle?

Bill asked me a great question on the Couplemate website yesterday. He asked “I want to invert my overlay axle, so my caravan gains extra height. Currently, it hits the top of the mudguard.”

So Bill here is our answer.

overlay axlesOverlay axles have changed over the years, so it is not possible for a straight-up and down answer.

Traditional Overlay axles had a 5mm camber so inverting these axles would have disastrous results. The image on the right is an overlay axle in its normal position.

The function of an overlay axle is to lower the car trailer or horse-float a little so that cars and horses have easier access. The centre of gravity will also drop.

The question of inverting an axle has advantages and risks. Here are our recommendations.


How much extra clearance do I gain by inverting my 45mm Square Axle?

The total gain by inverting a 45mm Square Axle is 90mm

Conditions allowing for inverting of the Overlay Axles

  • The stub axle has a weld within a position with zero camber.
  • The overlay is installed on top of the springs.
  • Axle spacer plates must be repositioned and welded to the axle.
  • Park brake to be relocated on top of the axle for 10” electrics.
  • Park brake to be relocated on the bottom of the axle for 9” mechanical brakes.
  • Stub axles to have a minimum of 50mm welded section.
  • Standard U-bolt are changed for heavy duty U-bolts.

inverted overlayTaboo issues are

  • Axles located under spring are a safety issue. In other words, a damaged U-bolt can easily detach and cause your axle to become separated.
  • Couplemate does not recommend under slinging axles except in exceptional circumstances. For example, where the keel on a boat trailer prevents axle installation. The manufacturer can invert or gull wing the axles.
  • Not welding in axle spacers in between spring and axle.
  • Stub axles welded on top of the hollow box section.
  • Welded section less than 50mm
  • 1/2″ u-bolt (higher centre of gravity required more clamping force to counteract the higher moving load forces)
  • You may require 5/8″ U-Bolts for inverted axles.

Furthermore, the higher centre of gravity you have installed by inverting your axle will require a change in driving habits.

As a result, the top-heavy rig will corner differently and behave differently on variation in road camber.

Long, wide overlays can create vibration fatigue.

There is a good article here about how to remove vibration and how to install shock absorbers to remove the effects of vibration.

Is it possible to invert straight beam axles?

Finally, you may need an engineering certificate when considering under-slinging your axle to raise the van, here are some considerations.


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