Effect of Steering System Compliance on Steered Axle Tire Wear

Subject paper focuses primarily on non uniform tire wear problem of front steered wheels in a pickup model. Cause and effect analysis complemented with field vehicle investigations helped to identify some of the critical design areas. Investigation revealed that steering geometry of the vehicle is undergoing huge variations in dynamic condition as compared to initial static setting. Factors contributing to this behavior are identified and subsequently worked upon followed by a detailed simulation study in order to reproduce the field failures on test vehicles. Similar evaluation with modified steering design package is conducted and results are compared for assessing the improvements achieved. In usual practice, it is considered enough if Steering Geometry parameters are set in static condition and ensured to lie within design specifications. However, during investigation it was noticed that in dynamic condition, excessive load variations on steering linkages and parts of suspension may result in disturbing the wheel alignment significantly enough to move these parametric values beyond their specification limits. Present study takes into account all such factors that contribute to this effect. However, special deliberation has been made to Ackermann steering geometry variations due to steering system deflection losses during the study. Ackermann Steering Geometry plays a vital role in ensuring steered wheels to demonstrate uniform tire wear by defining a relationship between front inside tire and front outside tire while vehicle negotiates a curve. Results of this study propose desirable Ackermann Error trend and suitable steering characteristics that lead to uniform tire wear. A steering axle duty cycle (used during the study) has also been proposed for accelerated front tire wear simulation testing of the test vehicles. Attempt has been made to achieve a similar tire wear on the test vehicles as obtained in field vehicles. The analysis helps to develop an understanding that dynamic geometric variations in the steering system may also significantly affect tire life of the steered wheels.