Although alignment concerns the wheel and the vehicle’s mechanical components that support it, an incorrect setting has a direct impact on tyres. For safety and economical reasons, it is important to check the alignment of the truck-trailer rig regularly and know how to detect a misalignment when abnormal wear is found on a tyre.
Small cause, big consequences
Like at school, for many of us, alignment is a matter of angles. On coach, bus, truck or trailer axles, four angles are measured: Camber, toe, caster and the kingpin angle. These are fine adjustments and an alignment that is one millimetre off may increase fuel consumption and reducemileage performance by up to 7%. In addition to the vehicle’s mechanical components suffering fatigue, a misalignment impacts the tyre’s service life, its rolling resistance and the driver’s safety, all good reasons for these angles to bechecked regularly.
A good angle of reflection
When a truck is viewed from the front, the camber is the angle between the wheel plane and the vertical axis, perpendicular to the ground. If the camber or negative camber is too high, the tyre contact area with the road is reduced. Furthermore, the load shifts to the tyre’s inner or outer shoulder, which results in premature wear.
Camber should not be confused with the kingpin angle, which is only measured on the steer axle. It is formed by the vertical and the pivot axis of the wheel, as viewed from the front.
Parallelism (or toe), as its name indicates, corresponds to the alignment of the wheels in relation to the vehicle's axis. A misalignment results in toe-in (the wheels point inwards) or toe-out (the wheels point outwards, like a duck’s feet). In this case, tyres are subject to a tearing phenomena andincreased wear across the tread . If the wheels are parallel to each other but are not parallel to the vehicle’s axis, then a misaligned axle may be the cause.
Finally, when the steer axle is viewed in profile, the caster angle is measured between the vertical and the steering axis. A correct caster angle ensures the self-alignment of steered wheels and means the driver does not have to constantly correct the steering.
On-site wheel alignment
Tyre specialist networks such as First Stop, Euromaster, Point S, Siligom… propose services to check and adjust the wheel alignment of trucks.These are common operations but they require bringing the truck to a service centre and hence, downtime for the tractor-trailer. However, in France, 85 % of fleet operators use on-site services. Several retailers propose this alternative, such as Euromaster or Massa. By making an appointment, highly trained wheel alignment specialists will come with a mobile workshop that contains all the equipment required to measure and correct the alignment.
By Renaud Lacroix