The UC Davis single-wheel traction testing machine has been used extensively to conduct field tests in an investigation of soil-tire interaction. These results have been used in the development of models for tire traction in deformable soils. A technique for measuring the three-dimensional dynamic contact area between a tire and the soil has been developed. Knowledge of the soil-tire contact profile, along with a model of soil behavior, permit accurate prediction of tire traction. Profile measurements are presented for two different sized tires in firm and tilled soil conditions at different inflation pressures and axle loads. Tractive forces were predicted by integrating normal and shear stresses over the contact, profile based upon a simple model of soil behavior.