Tire Transient Force and Moment Response to Simultaneous Variations of Slip Angle and Load

Nonsteady-state tire tests performed on Calspan's Tire Research Facility (TIRF) showed that at slip angle and load path frequencies of up to 0.2 rad/ft, attenuations of both lateral force and aligning torque are negligibly small. However, both quantities develop considerable lags at low path frequencies and, hence, show appreciable “dynamic” offsets, amounting to about 10% of the maximum steady-state values at 0.05 rad/ft (not uncommon in accident avoidance maneuvers).

Actual, double-lane change maneuvers performed on a skid pad with an instrumented full-size passenger car indicated dynamic offsets of about ±90 lb for lateral force and ±17 ft-lb for aligning torque. These data were reproduced with good accuracy in simulations on TIRF in which both load and slip angle were varied simultaneously in accordance with typical time histories recorded in vehicle tests. It is suggested that these large offsets could significantly influence the dynamic response of vehicles.