Examination of ATV Tire Forces Generated on Clay, Grass, and Sand Surfaces

A towed tire testing fixture suitable for use in testing all terrain vehicle tires is designed and built. Vertical loads on the tire under test can be varied from 100 to 400 1bf (445-1780N) and the camber and slip angles can be varied from 0 to 20 degrees. In addition, longitudinal slip measurements in braking are possible through the use of a disc brake assembly. Six strain gage loads cells are used to determine the force and moment resultants at the tire contact patch. Data acquisition and processing are done through a Daytronic 10KUD data pack and lap top PC.

This system is used to test seven representative ATV tires operating on surfaces of hard packed clay. Two of these tires are also tested on short and tall field grass, and on beach sand. Information on the lateral force coefficient, and the rolling resistance coefficient, as functions of vertical load on the tire, and slip angle of the tire, are generated. For the two tires tested on clay, grass and sand, one quadrant of the friction ellipse is determined showing the lateral force coefficient vs the braking force coefficient, with slip angle and longitudinal slip ratio as parameters.