Interface Pressures of a Tractor Drive Tyre on Structured and Loose Soils

An 18·4R38 radial-ply tractor drive tyre was operated at 10% travel reduction, at three correctly inflated combinations of dynamic load and inflation pressures on a structured clay soil and at another combination of load and inflation pressure on a loose sandy loam and a loose clay loam soil. Soil–tyre interface pressures on the face of one lug and on an undertread region between two lugs were measured, and were used in estimating the tyre footprint area for the operating tyre. On the structured clay soil, the interface pressures on the lug face were substantially greater than tyre inflation pressure and those on the undertread were considerably less than inflation pressure. On the loose sandy loam and the loose clay loam, some interface pressures on the lug face exceeded inflation pressure by only a small amount and others were a small amount less than inflation pressure, while undertread pressures were less than inflation pressure. Tyre footprint areas on the structured clay soil were nearly equal for the three correctly inflated load and inflation pressure combinations. The footprint area on the loose sandy loam was 10% greater, and that on the loose clay loam was 4% greater, than the average of the three footprint areas on the structured clay soil.