Abstract A single wheel test device was used to characterize soil strength in developing a prediction equation for dynamic traction as a function of wheel slip. Normal loads were placed on the single wheel, via hydraulic cylinder, and the maximum torque that could be developed was measured. The slope of the plot of normal load versus wheel torque was used as a parameter and a term defined as the test wheel numeric was introduced. The prediction equation was compared with a widely used method that relies on the cone penetrometer to characterize soil strength. The method using the single wheel tester was found to provide better predictions of dynamic traction ratios on a number of different surfaces.