On the Traction Tests: How They Affect the Performances of Tractor Tyre Combination

In the last decades improving efficiency became the predominant theme of tractors and tyre manufacturers. Performed traction tests on the field are the most helpful instrument for evaluating vehicle performances under different load conditions that can rapidly replicate real tractor configuration and usage. This work performed two traction test procedures with a New Holland tractor with continuously variable transmission equipped with Michelin very-high flexion tyres and wheel force transducers. This tractor was connected to another used as a braking unit and tested with two traction test procedures denoted as transient and steady-state procedures. In the former, the braking unit was driven at a fixed velocity and the pulling tractor increased the wheel velocity, progressively increasing the drawbar force. Instead, in the second, the pulling tractor was driven at a fixed velocity and the braking unit reduced its velocity at different levels thus applying a discretely increasing drawbar force. The collected data were analysed to evaluate parameters related to traction capability and efficiencies, such as vehicle traction ratio, traction efficiency and power delivery efficiency. Procedures were compared in terms of reproducibility, variability, and repeatability. Both test methods have pros and cons, but the steady-state procedure provided better accuracy in the results, an easier way to impose and control different test parameters, and the best test-to-test repeatability. The results of this work help understand how data collected by traction tests performed with the latest generation tractors could be affected by the testing procedures.