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A machine was built to study non-rolling tire stiffness and damping coefficient of agricultural tractor tires in the vertical direction. Measurements of static deflection and contact area on a rigid surface can be performed. During dynamic experiments, a sinusoidal deflection function is imposed to the test tire to determine dynamic stiffness and damping coefficient. The experimental setup and methodology are described in this paper. A complete sample test and its analysis are also presented. This paper was approved for publication by the Director of the Louisiana Agricultural Experiment Station as publication number 93-07-7238. Trade names are used solely to provide specific information. Mention of a trade name does not constitute a warranty of the product by the Louisiana Agricultural Experiment Station of the LSU Agricultural Center nor an endorsement to the exclusion of other products not mentioned. The authors are François P. Brassart, Graduate Research Assistant, and Malcolm E.

Vertical stiffness and damping coefficient values were measured, in non-rolling conditions, on eleven agricultural drive tires, with sizes ranging from 14.9-30 to 18.4-38, and both types of carcass construction, bias and radial, were tested. Tire stiffness was measured both in static and dynamic conditions. The mechanical model representing the tires was made of a parallel spring-and-damper system, simplified to a single spring in static conditions. Tire stiffness was linearly related to inflation pressure in all cases, but dynamic stiffness was higher than static stiffness. The use of different tire models for static and dynamic conditions is recommended during simulation and tire behavior prediction.