How Incorrect Caravan Axle Triangulation Destroys Tyres

Announcement posted by Couplemate Trailer Parts 08 Jul 2022

Caravan axle triangulation determines whether wheels are correctly set to run straight without the tyre scrubbing inside or outside.

Tyre scrub is different and can be either toe-in or toe-out. The latter occurs when the caravan components are overloaded, thereby causing tyres to tow out. This action causes wear on the inside of the tyre.

Unless the box section is welded square with the coupling, types will not run square or true.

Triangulation can also become out of proportion due to damage done to axles and/or chassis during a journey.

This article will consider two types of caravan wheel alignment:

Single Axle or beam
Independent Suspension

Further, in the case of a beam axle, misalignment could be caused by a bent axle. If the axle is bent less than 5mm, twist the axle until the bend points up on each end by 2.5mm. The entire caravan load should reduce this bend to less than 1mm.

Caravan Beam Axles

Caravan wheels that are misaligned in the case of beam axles are relatively easy to correct.

Refer to figure 1. Measure distances L and M to obtain the distance from the centre of the coupling to the tip of the axle or drum. This measurement must be accurate – ensure no sag in the tape measure and do not use elastic string. Maneuver the axle so that the size between M and L is equal. (slide the axle on top of the axle pad)
If the axle is poorly aligned, replace the axle pad with a short shackle plate. Place one hole over the spring centre and slide the axle over the shackle plate, backwards or forwards, until M and L are equal.
Install the u-bolt to apply a small amount of pressure to the axle during alignment.
When M and L are equal, tighten u-bolts.
Finally, weld the shackle plate to prevent axle movement during braking events.

Caravan repairers are experts in all types of suspension and recommend asking them if you need your wheel alignment assessed.

Caravan Service Agents we thoroughly recommend

Independent Coil Suspension

This installation or triangulation procedure only applies to Couplemate Independent Suspension only.

Set guards at a minimum of 110mm above the tyre.
Max compression 70mm with 35mm shock loading.
The measurement from the top of the frame to the centre stub is 297mm.
Top frame measurements, including shock absorber, mount brackets – 612mm x 300mm.
Bottom frame measurements, including shock absorber, mount brackets – 572mm x 300mm.
The Centre of the stub with the top fame measures 441mm from the front of the frame giving you 171mm.
From stub centre to rear of the top frame.
Suspension travel to full bump 70mm.
for every 30kg, spring compresses 1mm, or every 1kg equals 0.333mm
height of the suspension, from the ground to the underside of the chassis rail, would be half the diameter of your tyre (the stub centre) plus the measurement from stub to top frame 297mm. Therefore if
you have 265/70/16” wheels, the diameter is 777mm, your chassis will sit at 389mm plus 297mm, which equals 586mm.
When installing these frames to your chassis, it is essential to set these up correctly so that the frames are square with your chassis, with each other and that they toe in by 3mm.

Chassis Measurements

Refer to the figures below:

Measure distances L and M to obtain the distance from the centre of the coupling to the tip of the axle or drum. This measurement must be accurate – ensure no sag in the tape measure and do not use elastic string. Maneuver the independent suspension such that distance M is with 4mm of distance L.
Place a straight edge along the face of the drum/brake. This straight edge should be at least 1m long.
Measure distance O and N. Manoeuvre the independent suspension frames such that O and N are within 1mm of each other. Do the same with measurements P and Q.
Setting the toe-in. Refer to figure 2. Using the straight edges, measure distance R and S. Manoeuvre the independent suspensions such that distance S is 3mm shorter than distance R. During this process, both the independent suspensions should be moved the same amount to achieve the 3mm difference.
This is to ensure the toe-in is set equally on both left and right sides.

Figure 1

Figure 2

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