The Effect of Oversize Tires on Vehicle Dynamics and Crash Risk of Light-Duty Trucks

Aftermarket body and suspension lift kits and oversize tires can be installed to improve step-in height, customize the appearance or enhance the utility of light-duty trucks (“raised vehicles”). The modifications could considerably increase the center of mass height, kingpin offset and tire rolling tire diameter - changes that could interfere with the integration of original components and subsystems. The alternations could lower braking efficiency, increase rollover propensity, affect steady-state handling and transient cornering behaviour, raise the risk of suspension and wheel component failures, and change the geometric alignment of primary energy-absorbing systems. A study was conducted to examine the effect oversize tires may have on the crash risk of raised vehicles. Measurements were obtained from a representative sample of pickup trucks and sport-utility vehicles equipped with replacement tires that were measurably larger than original or optional tires stipulated by the original equipment manufacturer. The dimensional data were collected from 928 raised vehicles at 12 vehicle emission testing stations in British Columbia. Driver moving violation records, annual mileage, and crash-claims information from January 2003 to December 2005 were also obtained. Two independent analyses were conducted with the first evaluation using a multiple linear regression model to evaluate driver attributes and vehicle characteristics that could influence the involvement of raised vehicles in culpable crash-claims. A double-pair comparison was employed in the second analysis to calculate and compare the relative risk of the raised vehicles with oversize tires in at-fault crashes and other (non-altered) vehicles driven by the same drivers. The results from both analyses indicated that the crash risk of raised vehicles increased in proportion to the rolling tire diameter of oversize tires.