Three two-dimensional models were developed to predict the tractive performance of a tractor driving wheel, by integrating the forces over the interface with the soil. Each model used a different assumed shape for the interface; a horizontal plane plus part of the undeflected circumference, a sloping plane joining the frontmost and rearmost points of contact between the tyre and the soil and part of the circumference of a circle larger than the tyre. Results predicted from the three models were compared with data from experiments using a single wheel tester to measure the tractive performance of three different sizes of tractor driving wheels in the field. The best agreement between measured and predicted results was obtained with the model which assumed a sloping plane interface. It would be necessary to take account of torsional deformation of the tyre to improve the accuracy of the prediction method.
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