A Model for the Prediction of the Contact Area and the Distribution of Vertical Stress below Agricultural Tyres from Readily Available Tyre Parameters

The contact area and the stresses at the soil–tyre interface form the upper boundary condition of soil compaction models. Therefore, it is important to have good predictions of these stresses. For 29 combinations of wheel load and tyre characteristics, the contact area and the distribution of vertical stress directly below the tyre were measured. Characteristics of the contact area and the stress distribution were related to tyre parameters, and a model was developed that generates the contact area and contact stress distribution from readily available input parameters, namely wheel load, tyre inflation pressure, recommended tyre inflation pressure at given load, tyre width and tyre diameter. In the model, longitudinal distribution of vertical stress is described by a power-law function while transverse distribution of vertical stress is described by a decay function. The latter equation is powerful, as it is able to describe different cases of stress distribution, e.g. maximum stress under the tyre centre or maximum stress under the tyre edge. The shape of the contact area is described by a super ellipse. The model presented provides significantly improved input data for soil compaction models and hence increases the accuracy of predictions of soil stresses and soil compaction.