The effects of tyre systems on the depth and severity of compaction

High value crops such as peas for the frozen vegetable market have to be harvested at the optimum point for quality, regardless of field conditions. Six wheeled pea harvesters with a gross weight of 27 t, giving a wheel load of 4.5 t are required to move from field to field with optimum timeliness. In order to achieve road speeds of 25 km/h an inflation pressure of 2.2 bar is required for the specific tyre load speed rating. Typically, in field conditions, this inflation pressure is not reduced and therefore the likelihood of soil damage is increased. This study was undertaken to examine the effects of tyre section width and inflation pressure on rolling resistance, rut depth and sub-surface soil deformation. Under controlled laboratory conditions three tyres, at three inflation pressures, with a load of 4.5 t were passed over a soil at three different initial bulk densities. Measurements of dry bulk density, rut depth, rolling resistance, cone penetrometer resistance and soil deformation through the profile were taken before and after the passage of the tyres. The results show that by increasing the tyre size and reducing the inflation pressure the depth at which compaction occurs and rut depth decrease by 44%. The 800 mm section tyre causes less compaction than any of the other tyres tested especially when inflated to 1.6 bar. Rolling resistance is reduced when the tyre is inflated to the optimum for each tyre. The change in bulk density when plotted against either initial bulk density or penetration resistance results in a set of curves which can be used by the manufacturer, farmer or operator to select the correct tyre section width and inflation pressure for field conditions. As a result of this study the harvester manufacturers are investigating the engineering requirements of increasing tyre section width to 800 mm and are now equipping pea harvesters with central tyre inflation systems. The benefits of which would be to significantly reduce the amount of soil compaction, reduce rolling resistance and save the operator £455 000 per annum in fuel costs.