Abstract: An electronically controlled suspension apparatus is provided for manipulating the spring constant of a bicycle rear wheel suspension system. The suspension apparatus includes a gas shock absorber connected to an external fluid chamber via a discharge loop and a return loop. The two loops control the volume of gas in communication between the shock absorber and the fluid chamber. The discharge loop includes a fluid control valve and a flow rate control valve. The return loop includes an one-way check valve and a flow rate control valve. The present invention also includes a sensor for measuring terrain induced accelerations of the rear wheel and an electronic circuit for operating the fluid control valve.