Comparison of the tractive performance of a tractor driving wheel during its first and second passes in the same track

The tractive performance of a conventional 13.6–38 tractor driving wheel tyre was measured in 19 different fields using the NIAE Single Wheel Tester. In each field the performance was measured on the undisturbed ground and again in the rut formed by a previous run with the same tyre. The second run simulated the operation of the rear wheels on a four-wheel drive tractor.The performance during the second pass was generally better than during the first pass. On average, the coefficient of traction increased by 7%, rolling resistance reduced by 11% and maximum tractive efficiency increased by 5%. The improvement increased as ground conditions deteriorated but was never large enough to fully explain the differences in performance between two and four-wheel drive tractors previously measured. It is suggested, therefore, that these differences may be primarily due to the greater ease with which power, weight, implement size and working speed can be matched with four-wheel drive tractors.