Tractor traction tyres interact with soil by a system of normal and tangential stresses along the soil-tyre contact surface. In this interaction both soil and tyre deform according to their own stress-strain relationships. Soil deformation results in the formation of a rut as well as in topsoil displacement along the soil-tyre contact surface. The topsoil displacement depends on shear stress which soil undergoes at contact with tyre. The shear stress-displacement relationship characterizing the soil layer which interacts with the traction tyre has been studied for a long time as it strongly affects the relationship between traction force and wheel slip, usually referred to as traction performance of the soil-wheel system (Becker, 1956; Janosi and Hanamoto, 1961; Wills, 1963; Wong and Preston-Thomas, 1983)