A variable stiffness suspension system is provided for a wheelchair. The wheelchair has a frame and at least one wheel coupled to the frame for generally vertical movement relative to the frame. At least one sensor is provided for sensing an operating condition of the wheelchair. A controller is operatively coupled to the sensor. A controllable damper having a variable stiffness is coupled to the controller, the wheel and to the frame. The controllable damper is responsive to the controller and provides a force capable of being varied in a continuous manner. The force is resistive to movement of the wheel. The controllable damper is preferably a commercially available magneto-rheological damper or a variable orifice fluid damper. The controllable damper may be either a linear damper or a rotary brake.