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This study fills some of the information gap on how heavy truck axle alignment evolves from what is set at the factory to what exists at delivery and after several thousand miles of use. Alignment parameters were caster, camber, toe, and tandem skew. The results give insight to alignment specifications based on measurement capability / repeatability, the evolution of alignment “changes”, and conclusions on desirable alignment practices for OEMs and user fleets.

A seven-company, cooperative evaluation was conducted to investigate the effect of camber and toe on the original tread life of steering axle tires in an operational fleet of Class 8 tractors. A total of 31 set-back-front-axle tractors were configured with steering axles that had one of the following nominal camber values: -3/4 deg, -1/4 deg, +1/4 deg, +3/4 deg, or +2 deg on the left and 1/4 deg more negative values on the right. Toe was then adjusted to one of three nominal settings (+0.140 in., +0.040 in., or -0.060 in.). Tire wear data were gathered over an almost two-year period. Relative tire wear as a function of camber and toe are presented.

It is generally accepted that steering axle tire wear rates are considerably higher in turns than in a straight ahead condition. Ackerman correction accounts for the different turning radii of the left and right steering axle tires in a turn but does not take into account slip angle. Slip angle is a significant factor in tire wear. “Optimum Ackerman” does take slip angle into account and should theoretically reduce tire wear. Theory, simulations, and field results are presented.