Abstract: A relational equation between the torsion angle of a torsion bar and theroughness of a road is obtained by analyzing a torsion bar road wheeldynamics model for a simplified tracked vehicle. Based on the equation, thetorsion angle is calculated against the roughness of the road and vise versa.A numerical example combined with the ADAMS simulation verifies the feasibility ofthe method to calculate the roughness of a road upon the measured result of a torsion angle.