ASABE Technical Library - Abstract

Abstract. Loading soil with agricultural vehicles is a major cause of compaction of agricultural soils. The loads applied to the soil and the resulting pressure influences the degree of soil compaction. This study was conducted to determine an effective method to measure the pressure distribution under a selection of pneumatic agricultural tires and based on this the tire carcass stiffness was determined and methods to predict carcass stiffness were evaluated.

The tire carcass stiffness is defined as an equivalent pressure resulting from the tire carcass stiffness and estimated by subtracting the tire inflation pressure from the mean surface contact pressure. To measure the carcass stiffness of a tire the following approaches were considered:

The ink footprint method to estimate the size of the contact patch and hence mean contact pressure,

Tire load – deflection method,

The pressure mapping method to measure both mean and maximum contact pressure using a commercial pressure mapping system

Tire manufacturer’s specification data methods (two variants).

Carcass stiffness values obtained from the ink footprint method gave results significantly lower (30 – 40%) than those obtained using the pressure mapping system. The method based on the tire load – deflection characteristics was found to give a better estimation of the tire carcass stiffness of the smooth rather than the treaded tire. The technique of using the theoretical load that the tire is able to sustain at zero inflation pressure, produced estimates that were within ± 20% of the mean carcass stiffness determined using the pressure mapping system. It is recommended that this method should be used in the absence of a pressure mapping system and it would be beneficial to users if the results of this could be added to the tire manufacturer’s specification data.