A mechanical seat suspension inside a housing comprises parallel scissor arms and a support arm with a cam connected to suspension springs. The support arm, which carries the substantial majority of the seat load, has a height adjustment means and a cam with two arcuate surfaces that define an imaginary pivot point. The use of the cam with the imaginary pivot point permits a more compact structure. Various embodiments of the support arm with a cam end and devices using the support arm are also disclosed. A shock absorber attached to the outside of the scissor arms dampens the stroke of the suspension springs connected to the cam. The ratio of the shock stroke travel to the vertical movement of the seat remains generally linear and constant, thus producing a more comfortable ride. Also included is a height adjustment mechanism on the support arm that interlocks with the cam by a pivoting pawl and biasing spring. The height of the seat is adjusted by the relative movement of the top portion of the housing to the lower portion. No external levers, triggers, or other structures are necessary for seat adjustment. The tension in the suspension springs is adjustable to compensate for the weight of the rider.