Potential of three-dimensional footprint mold in investigating the effect of tractor tire contact volume changes on rolling resistance

In the present study a method is developed to estimate the three-dimensional (3D) footprint of pneumatic agricultural tires based on molding the tire footprint by liquid plaster and converting these molds to three-dimensional models using a 3D scanner. A Goodyear 12.4-28, 6 ply tractor drive tire was operated on a clay loam soil in a soil bin under three vertical loads, using three inflation pressures and three soil moisture contents at a constant forward speed of 0.45 ms-1. The results showed the rut depth and contact volume increased by increasing the vertical load and inflation pressure and soil moisture content. Contact volume was increased by increasing the vertical load, inflation pressure, and soil moisture content. A multiple regression model was presented with a coefficient of determination (R2) of 0.88 to predict the contact volume based on vertical load, inflation pressure, and soil moisture content. Finally, a univariate regression model was presented to predict the rolling resistance based on the contact volume with a relatively high R2 of 0.93. It was also found that in deformable surfaces, vertical penetration and soil contact volume are the main reasons for the increase in rolling resistance.