Beam Axle Triangulation Guide

How to Check and Correct Trailer Axle Alignment

Correct axle alignment (triangulation) is essential for safe towing, straight tracking, and even tyre wear. Poorly aligned axles can cause excessive tyre wear, unstable towing, and increased stress on suspension components.

This guide explains how to check and correct beam axle triangulation on caravans and trailers.

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What Is Axle Triangulation?

Axle triangulation checks whether the axle is square to the coupling and centred in the chassis.

It involves:

• Measuring from the centre of the tow coupling to each end of the axle

• Confirming both sides are equal within tolerance

• Ensuring the axle is centred between the chassis rails

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Tools & Equipment Required

• Tape measure (rigid – no string or elastic)

• Plumb bob or towball-locating measuring tool

• Spanners or impact gun for U-bolts

• Jack and axle stands

• Wheel chocks

⚠️ Safety first:
Always support the trailer safely before working underneath.

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Step-by-Step: Axle Triangulation Procedure

1. Prepare the Trailer

• Raise the caravan or trailer safely

• Remove the wheels

• Remove the hub caps from the hubs

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2. Establish the Coupling Centre Point

• Hang a plumb bob from the centre of the coupling through the adjustment screw
  OR

• Use a purpose-made tool that locates in the towball socket

This point is your reference centre for all measurements.

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3. Measure Coupling to Axle – Side A

Measure from the centre of the coupling to the front edge of the axle on one side.

This is Dimension A.

📌 Important measurement notes:

• Keep the tape straight with no sag

• Do not use string or elastic materials

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4. Measure Coupling to Axle – Side B

Repeat the measurement on the opposite side of the trailer.

This is Dimension B.

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5. Compare A and B (Triangulation Check)

• The difference between A and B must be less than 4 mm

• If the difference exceeds 4 mm, the axle must be realigned

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Checking Axle Centralisation

Even if triangulation is correct, the axle must also be centred in the chassis.

6. Measure Chassis to Hub Face

Measure:

• From the outside of the chassis rail to the hub face on one side (Dimension C)

• Repeat on the other side (Dimension D)

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7. Compare C and D

• The difference between C and D should be less than 5 mm

• If greater than 5 mm, the axle must be recentred

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Correcting Axle Position

8. Re-Centralising the Axle

• Loosen the U-bolts securing the axle to the springs

• Slide the axle sideways until:

  • Dimensions C and D are within 5 mm

• Recheck measurements before proceeding

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9. Realigning (Triangulating) the Axle

• Loosen the U-bolts on one side only

• Move the axle forward or rearward as required

• Tighten U-bolts to the correct torque

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10. Final Check

• Re-measure triangulation (Steps 3–5)

• Adjust again if required

• Once correct:

  • Refit hub caps

  • Refit wheels

  • Lower trailer

  • Torque wheel nuts correctly

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Tandem Axle Trailers

For tandem axle trailers, this entire procedure must be repeated for the second axle.

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Acceptable Tolerances (Quick Reference)

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Why Correct Axle Alignment Matters

• Reduces tyre scrub and uneven wear

• Improves straight-line towing

• Reduces suspension and bearing stress

• Improves braking performance

• Prevents long-term chassis damage

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Source

This guide is based on the AL-KO Beam Axle Triangulation Procedure – May 2024.

Beam-Axle-Triangulation-Procedu…