Air vs gas shocks - an explanationby forum member madizazzo
When a shock absorber is referred to as a "Gas Shock" it means that a charge of an inert gas, almost always nitrogen, has been installed inside the fluid chamber of the shock absorber.
All shocks have some free air space above the fluid to allow for expansion and contraction of the fluid due to ambient air temperatures and the heat generated by the action of the shock absorber. By using a pressurized inert gas, foaming of the fluid used in the shock absorber is greatly decreased. This provides more consistent shock absorber action.
Many OEM shocks and most aftermarket shocks are gas filled, but the pressure used varies. The gas pressure, no matter how high it may be, can not provide for any measurable amount of lift compared to the vehicle's springs.
An "Air Shock" on the other hand is a shock absorber with an air bladder to provide more lift by using compressed air as a spring. They don't work all that well on automobiles and are useless on a truck or Motorhome. That's because the air bladder is small, because of the restricted space available for them.
A shock absorber can be BOTH an air shock and a gas shock. The two names describe separate properties of a shock absorber.
If an air spring has 100 pounds per square inch pressure, and it's internal cross section area (minus the shock absorber body it's wrapped around) is 2 square inches, then it provides a lift of 200 lbs.
The biggest drawback air shocks have is the small air bladder and high pressures they need to operate. A property of an air bladder (air spring or air shock) is that if the air bladder is compressed to one-half of it's height, the air pressure has doubled. This makes a rapidly rising spring rate on bumps, making the ride harsher.
Because of the high air pressures required to add lift to a 9,000 to 14,000 lb. vehicle, when the vehicle hits a pothole or bottoms out, the air pressure will go sky high, and air shock life on a heavy vehicle is usually poor.