Increasing demand for enhanced riding comfort has made it important to consider longitudinal vibration which contributes to riding comfort. This study analyses the longitudinal vibratory forces acting on the unsprung mass and verifies with calculations and experiments that longitudinal vibration can be reduced by offsetting the vibratory force attributable to the tyres with vibratory forces generated by the shock absorber and longitudinal principal axis of elasticity. It also describes a way to arrange the shock absorber and the longitudinal principal axis of elasticity that reduce the longitudinal vibration.