A shock absorber includes a cylinder; a piston movable therein and dividing the cylinder in first and second cylinder chambers; a cylinder attachment for attachment to a first part of a vehicle and connected to the cylinder; and a piston attachment for attachment to a second part of a vehicle and connected to the piston. The piston attachment and cylinder attachment move towards one another on an inward movement and away from one another on an outward movement. The piston includes a first inward channel; a first inward valve to open the first inward channel on inward movement; a first outward channel; a first outward valve to open the first outward channel on outward movement; a second inward channel; a second inward valve to open the second inward channel on inward movement; a second outward channel; and a second outward valve to open the second outward channel on outward movement.