Calculation of normal tire stiffness for tractors and agricultural machinery based on the loaded wheel radius

BACKGROUND: To preserve the physical properties of soils, manufacturers of agricultural machinery use tools to reduce the pressure of the chassis supporting elements on the ground. One of them is reducing tire stiffness. The normal (radial) stiffness of a tire determines its ability to deform and the geometric parameters of the contact patch, which determine the pressure on the soil. The values of the normal tire stiffness during design modeling of the motion of tractors or agricultural machinery are calculated using existing universal experimental dependencies that are not specialized for tractors and agricultural machinery. AIM: Development of a method for calculating the normal tire stiffness for tractors and agricultural machinery based on the loaded wheel radius. METHODS: Calculations of the normal stiffness of the tires with a given free radius at normalized tire pressure and vertical load for tractors and agricultural machinery were carried out according to the new proposed method using the loaded radius. The used software products are Excel, MatLab, Curve Expert Professional. RESULTS: A method has been developed for calculating the normal (radial) stiffness of an agricultural tire of a given free radius at a given load and internal pressure, based on the use of the loaded wheel radius. Using the obtained method, the stiffness of 93 tires for tractors and agricultural machinery was calculated. The maximum error in calculating the stiffness of agricultural tires using the proposed method was 20% for radial and diagonal tires and the average error was 6% for radial tires and 10% for bias tires. CONCLUSION: A method for calculating the normal stiffness for agricultural tires using the loaded wheel radius has been developed and implemented. The method can be used in design modeling of the motion of a tractor or an agricultural machine.