The Detachment of Wheels from Commercial Vehicles

Detachment of wheels from heavy commercial vehicles has been noted in the UK. The mechanism appears to be that of a clamping failure. The compressive force of the wheelnut does not generate enough frictional holding power to prevent microscopic movements taking place between the wheel and nut. When this occurs the studs will be rapidly fatigued in bending and in addition the wheelnuts may loosen.

The forces imposed by cornering reduce the compressive forces under the wheelnuts. In-plane forces, such as the ground reaction, may then be sufficient to overcome the frictional hold. The reduction of clamping force is larger when the stud is stiff.

Dimensional inaccuracies make a key contribution to the problem. They arbitrarily change the designed flexibilities, they introduce fitting stresses and they create the difference in perimeters necessary for wheelnut loosening.