A guide to correct wheel alignment on trailers
Correct wheel alignment on trailers can prolong tyre life and decrease fuel consumption. It’s also a lot safer too, says Tom Coad at AES UK.
It is estimated over 50% of trailers on UK roads are out of alignment, with fleet operators often focusing on tractor units and overlooking trailers due to the nature of how they’re exchanged. AES believes there are enough benefits for larger fleets to consider corrective wheel alignment on trailers including:
- Tyres cost savings – up to 15% savings on tyres costs with correct wheel alignment
- Fuel savings – a correctly aligned trailer can reduce the pulling force (drag) on the towing unit lowering rolling resistance
- Safety – misaligned trailers often take up more room on the road due to “dogrun” or “crabbing” this can create uncomfortable and unsafe handling properties for the driver
- Environment – fuel and tyre cost savings reduce your CO2 emissions and tyre dust pollution
Below we have outlined how trailer alignment can affect the tractor unit and detailed ways in which technicians/fleets can fix out of line trailers.
How does a misaligned trailer affect a tractor unit
1- The rear axles of the trailer are out of square. One is negative, the other positive indicated by the blue arrows. Each axle rolling in different directions
2- Opposing forces are created which work against the frame of the trailer
3- This results in a lateral force which pulls the front of the trailer to the left which is transferred over to the tractor unit’s towing axles and even the front axle can receive undesirable lateral pulling force
4- This force must be counteracted by a lateral force which is created by steering the front wheels to the right. Hence, the driver needs to steer to the right to keep a straight-ahead direction on the road
This creates abnormal tyre wear on the front wheels of truck as well as the trailer itself.
Measuring a trailer
Wheel alignments on trailers can be carried out easily in-house with specialist equipment or by trained contractors. It’s important that the axles are aligned to the frame of the semi-trailer rather than to each wheel, the reason being if one axle is out of line using that as a reference will result in the other axles being out of line.
Misaligned trailer axles
Once you have measured the axles of a trailer you are looking for what we call “out of square”, essentially the rolling direction of the axle in relation to the centreline created with the wheel alignment system. And “parallelism” which looks at how all the axles are in relation to each other.
Adjusting trailer axles
Once you have identified which axles require adjustment we suggest adjusting to OEM specifications but have outlined some examples below.
Axle with eccentric bolt or axle:
Adjust out of square by turning the eccentric bolt or axle to the desired value. The adjustment will affect the individual toe values on both sides simultaneously. Pay attention to parallelism to frame centreline and between the other axles.
Adjust out of square by moving the eccentric plate
Adjust out of square by moving the adjustment washer up or down until the desired out of square value is obtained for the axle. The adjustment will affect the individual toe values on both sides simultaneously. Pay attention to parallelism to frame centreline and between the axles.
