Tire Cornering Force Test Method for Winter Surfaces

Tire cornering forces are often measured in the laboratory on a high-friction surface and little information exists on the nature of cornering on other surfaces. Thus, the impact of winter roads on vehicle behavior is difficult to fully capture in vehicle dynamics simulations. The CRREL (Cold Regions Research and Engineering Laboratory) Instrumented Vehicle was used to measure cornering forces on winter surfaces. The vehicle was instrumented for forces, speeds, and a variety of other measures. Tests were performed at the Keweenaw Research Center in Northern Michigan, during February 2005, and included measurements on ice, packed snow, and undisturbed snow. Packed snow density was 0.5 g/cm³ and loose snow densities ranged from 0.07 to 0.23 g/cm³ with depths from 5 to 23 cm. The test technique involved towing the vehicle in a straight line while sweeping the steering angle from zero to approximately 17 degrees both left and right. Both front wheels were free rolling and the vertical, longitudinal, and lateral forces were measured at the tire-snow interface. The data were reduced to evaluate the shape of the lateral force v slip angle curves and to compare maximum lateral force coefficients for different winter surfaces. Generally, the force v slip angle curves for ice reach a maximum value and then decrease. The packed snow curves climb more gradually and reach 90% or more of their maximum value by 7 to 10 degrees. The lateral forces for fresh snow surfaces continue to increase throughout the slip angle sweep, particularly for deeper snows.