An integrated and self-contained suspension assembly having a gas spring integrated with a shock absorber (damper) is described. The rigid gas cylinder of the air spring is divided into a first gas chamber and a second gas chamber. A flow port connects the first and second gas chambers, and can be manually opened or closed by valve and a simple one-quarter turn rotation of an external knob to instantly switch the gas spring between two different spring rates. The different spring rates are functions of the separate or combined volumes of the two gas chambers. The integrated suspension assembly is compactly packaged and self-contained, i.e., does not require any externalities, such as gas sources or electricity, to operate.