Tyres and Axle Alignment Issues

The safety and efficiency of truck tyres comes down to a topic often discussed, tyres and axle alignment issues.

There are many factors that contribute to abnormal tyre wear. However, the single biggest source of irregular tyre wear is from tyre pressure. This is usually due to low or uneven pressure, but on occasion, may be due to too high a pressure. Even a pressure of only 70 kPa (10 psi) above the recommended tyre pressure can result in almost as much abnormal wear as if it were 70 kPa (10 psi) too low.

Note: Always set tyre pressure to that recommended by the tyre manufacturer for the load, size and type of tyre and whether it is dual or single wheel configuration.

Application is another cause of uneven tyre wear. For example, tight turns on bitumen will cause tyre scrubbing. This scrubbing effect is especially significant on the tyres of a triaxle or quad group.

Other causes of tyre wear are over loading, uneven loading, tyre balance, improper or faulty brake operation, inoperative shock absorbers, incorrect axle alignment or a twisted chassis frame.

Wheel Alignment Overview

Due to their inherent design, camber and toe-in do not normally affect tyre wear on Hendrickson INTRAAX axles. A small amount of positive camber is built into INTRAAX axles sold in Australia and toe-in will be within a tolerance. Neither of these two specifications are adjustable and will generally only be out of specification if there is a problem with the axle.

Thrust Angle

The thrust angle of each axle is the most important wheel alignment angle for trailer axles. Variations in thrust angle between axles on the same trailer form a scrub angle.

Scrub Angle is the difference in thrust angles between axles. As the name suggests, scrub angles do cause tyres to scrub and wear due to each axle attempting to follow a different direction as they travel down the road.

Alignment Check

There are several checks that need to be carried out before carrying out axle alignment checks. 

1. Only check trailer alignment in an unladen state.
2. Check the wheels for runout and correct if necessary.
3. Settle suspension by moving trailer backward and forward in a straight line and leave parked on a hard level surface. 
4. Block at least a couple of wheels.
5. Release the parking brake.
6. Set kingpin height to that specified by the trailer manufacturer.
7. Set trailer ride height to the designed ride height.

Laser alignment equipment allows for greater repeatable alignment accuracy. However, it is also possible to carry out suitable alignments using simple equipment, such as with a kingpin extender and wheel end extenders and a suitable steel tape measure.