This paper focuses on the lateral motion of the automobile considering roll dynamics at high speed. The equation of motion of the vehicle response to steering input considering coupling motion between roll and lateral direction is theoretically solved by means of replacing roll motion by tire equivalent lateral deformation. The result shows that the effect of the coupling motion reduces yawing damping ratio, keeps the yawing natural frequency, and delays yawing response to steering input. Moreover, good agreement is found between the theoretical and experimental frequency response to steering input.