Wheel Attachment Failures in Light-Duty Vehicles

The frequency of vehicle accidents attributable to wheel attachment failures on light-duty (non-dual rear wheel) vehicles was extremely low prior to the advent of cast and forged aluminum alloy and forged “styled steel” wheels in the early 1970s. The sharp increase in such accidents which accompanied the rapid increase in the popularity of the more attractive solid wheels was attributable to a widespread failure among many after-market (and some OEM) suppliers and service organizations to recognize that the stiffer cast and forged wheels required more stringent installation and maintenance standards than did the more “forgiving” stamped steel predecessors. Coincident with, but not in response to, the increased frequency of wheel attachment failures on light-duty vehicles, hub-piloted wheels were introduced on heavier (dual rear wheel) vehicles as a means of reducing the long-standing higher frequency of attachment failures on vehicles equipped with the heavy-gage forged steel wheels. This reduction was accomplished by increasing the portion of the installation torque converted to wheel clamp force through a reduction in the portion lost to nut-to-wheel friction. Failure on the part of some investigators to recognize the factors responsible for the increased incidence of wheel separations on light-duty vehicles and the unique features of hub-piloted wheels gave rise to the formulation and propagation of myths and misconceptions regarding the causes and cures for such separations. It is the purpose of this article to identify critical features of wheel and wheel attachment designs and of their installation and maintenance requirements that relate directly to attachment failures and to dispel some of those myths and misconceptions.