A tire model for vehicle motion analysis on dry sand

In order to perform vehicle motion analysis, a model of the interaction between the traveling tire and the ground surface is necessary. The interaction model or the tire model needs to adequately obtain the forces exerted on the tire based on the ground characteristics, besides being simple and easy to use. This research aims to construct a simple tire model for the motion analysis of a vehicle traveling on dry sand. A single small rubber tire was driven on evenly flattened dry Toyoura standard sand to measure the longitudinal and lateral forces on the tire. During the wheel drive test, the tire was dug into the sand to keep the sinkage constant. In addition, the tire was given a sideslip angle, which is the attack angle to its travel direction. The collected data demonstrated that the sand–tire interaction produces a tire force in the same direction as the tire slippage, and the definition of the tire force norm for each sinkage value well approximates the data using a single curve independent of the sideslip angles. By using those characteristics, the tire model can be expressed by relatively simple functions of the sideslip angle and sinkage. A turning motion experiment on a four-wheel model vehicle on evenly flattened sand was conducted, and the result was compared with the result from the numerical simulation with the tire model, which confirmed the model’s accuracy.