Construction of modern wide, low-inflation pressure tyres per se does not affect soil stress

Abstract

The interaction between rolling gear and soil is complex, but most important for the stress distribution in the soil profile. We explored the effect of three types of wide, low-inflation pressure tyres with similar dimensions on mean normal stress throughout the soil profile. We first tested the hypothesis that the stress is not affected by specific tyre-construction. Second, we tested the benefit of lowering the tyre inflation pressure to a minimum for the tyre with the lowest recommended inflation pressure. Finally, we tested the effect of tyres with similar tractive potential at different wheel loads, i.e. with a different weight-pull ratio. Stress measurements were made with Bolling probes at six positions simultaneously: both beneath the centreline (centre) and at 0.3 m lateral distance (+0.3 m) of the centreline of the wheel track, at 0.2, 0.4, and 0.6 m depth. The results revealed a very limited effect of tyre construction on mean normal stress. No differences were measured beneath the centre, and the differences at +0.3 m were found only at 0.2 m depth for the tyres at the rear axle. The effect of minimising tyre inflation pressure was limited to the upper parts of the soil profile for the measurements beneath the centre of the tyre (significant at 0.2 m depth and a trend at 0.4 m depth). Finally, our study did not reveal significant benefit of tyres with a lower wheel load while potentially having similar tractive performance, although the reduction of wheel load and associated lower inflation pressure potentially reduce stress in both top- and subsoil. The results emphasize that in order to reduce soil stress, tyre design and use should allow for a large contact area and low inflation pressure.