What causes abnormal tire wear when a truck's wheelbase has been lengthened?

Lengthening a truck's wheelbase can lead to abnormal tire wear due to changes in the geometry of the steering system, particularly the steering arm angle. When the steering arm angle is incorrect, it affects how the wheels respond when steering inputs are made. This misalignment can lead to improper camber or toe settings, which in turn causes uneven contact with the road surface.

As the truck turns, if the steering arm angle does not allow the wheels to pivot correctly, it may result in one side of the tires wearing more quickly than the other. Over time, this uneven loading will lead to abnormal tire wear patterns, such as cupping or scalloping. Proper steering geometry, which includes the correct steering arm angle, is essential for maintaining even tire wear and ensuring that the vehicle handles predictably and safely. Therefore, the correct answer highlights the importance of adjusting the steering arm angle appropriately to accommodate the change in wheelbase.