Abstract: Preferably, a ski or like member contacting the ground suspends a snowmobile frame or chassis via vertical telescoping tubes defining a variable volume chamber. A hollow piston rod fixed to an end cap at one end of one of the telescoping tubes bears at its opposite end and slidable within the other cylinder, a damping piston. The damping piston bears a plurality of orifices for permitting restricted flow of hydraulic liquid to opposite sides of the piston and between chamber sections separated by the damping piston. The hollow rod opens at the end bearing the piston, directly to one chamber section, and bars at least one radial port adjacent its opposite end opening to the other chamber section with the port being closed off by an expandable O-ring functioning as a check valve. A given mass of hydraulic fluid is supplied to the chamber, and the chamber is gas pressurized.