Rolling resistance and rut formation by implement tyres on tilled clay soil

The rolling resistance and rutting incurred by towed flotation implement tyres were investigated on an arable clay soil in three different soil strength conditions. Three radial (600/55R26.5) and two bias ply (600/55–26.5) tyres were compared. Experimental wheel loads were in the 35.4–36.4 kN range. Tyre inflation pressures, representing typical field operation, and road transport applications were in 100–150 kPa and 150–200 kPa, respectively. Soil strength was determined from mean soil penetration resistance (CI0–15, in the layer 0–15 cm) and mean cohesion (C0–10, 0–10 cm). Wheel rolling resistance evaluated by the coefficient of rolling resistance (CRR), rut depth (RD), driving speed, and field gradient were measured with the tyres mounted on a test trailer hitched to a tractor. CI0–15 and C0–10 values predicted the sinkage and the resistance to travel motion on clay soil reasonably well. When the CI0–15 was less than 1 MPa and C0–10 was below 100 kPa, CRR and RD increased rapidly. On average, CRR was 20% lower for the radials than the bias plies. In soft conditions (CI0–15 ⩽ 0.48 MPa), the radials produced 15% shallower ruts than bias plies, and the CRR was lower and RD shallower with field inflation pressures than with road pressures used. According to our results, flotation tyres can be recommended to agricultural machines when the implement or trailer is used in soft soil conditions.