Rolling resistance of off-road vehicles

The rolling resistance (RR) of vehicles operating off-road is, despite its significance, an uncertain factor in haul-time and productivity estimates. The rule-of-thumb formula used for estimating the RR consistently underestimates the RR of free-rolling (nondriven) tires. The RR of driven tires is shown to vary considerably with the applied torque; at high torque (in low gears) it may be several times greater than the RR of free-rolling tires. This increase of the RR may result in a decrease in productivity, or at worst, in the immobilization of off-road vehicles. The use of an analytical tire-soil interaction model is a rational method of estimating the RR of both free-rolling and driven tires and, by summation, the total RR of wheeled off-road vehicles. Performance data sets consisting of rimpull and RR values for various values of slip, obtained from this model, present a realistic simulation of the interaction between vehicle and soil. Their use in conjunction with rimpull-speed relations supplied by manufacturers improves haul-time calculations and allows the performance of unbiased comparative analyses of various candidate vehicles for a variety of routing and soil conditions.