Motorcycle suspension systems

In a motorcycle frame having a generally closed configuration having generally horizontal upper and lower frame members and spaced generally front and rear vertical members transverse to and connecting said upper and lower members to form the closed configuration, a power unit in said frame, having a drive sprocket, the improvement comprising a pair of spaced generally horizontally extending swing arms on each side of said frame and rear wheel extending rearwardly from the rear member and each pivoted adjacent one end on said frame, a generally vertical link connecting the other ends of said swing arms and adapted to receive an axle shaft of the rear wheel intermediate the two swing arms, link means connected at one end to one arm of one of said pairs of swing arms, spring means pivotally connected at one end to one of a swing arm of the other pair of swing arms and the frame and at the other end to said link means at its other end said link meas being relatively proportioned to the spring means connection at said one end so that deflection of said swing arms from a first normal position upwardly around their pivot at the frame causes a progressively rising rate of deflection of said spring means, while maintaining both a substantially constant contact patch between the rear wheel and a surface being travelled and a substantially constant wheel base.