Agricultural tire footprint shape correlation to treads penetration in different soils

Aim of this work is looking for a correlation between footprint and soil penetration volume of treads in agricultural tires. Three tyres of different dimensions, fitted on the same tractor with different pressures and loads (N=not ballasted; Z=ballasted) were tested for defining the area of the single footprint shape (SF and SaF), of the multiple footprint shape (MF) and the volume of tyre in soil (V). Footprints were obtained on rigid surface (SF and MF) and on soils (SaF: sand) with different penetration resistance (soil cone penetrometer value). Contact area and void area (SF BW) were determined by a software that reads the footprint as an array of pixels in which black pixels and white pixels were distinguished. Volume of treads was measured from plaster mould. The correlation between tires’ footprint surface and volume of penetrated treads has been studied. Soil properties have effects on values but don’t have influence on trend in test conditions. Volume of penetration is due mainly to the surface in which treads lean. In the same surface results are influenced by ballast and by inflation pressure. Like in previous study, the use of the ellipse method on image from sand doesn’t allow to obtain high correlation with rigid surface, so this application, that with the volume could give the effective interaction between tire and soil, need more studies. The high correlation between data by volume on soil and data by multi-footprints give the possibility to read the interaction tire-surface by two different way.