Shocks filled with nitrogen or another gas help alleviate vacuum and cavitation through thermal expansion. A twin-tube gas-charged damper has a low-pressure charge of nitrogen gas in the reserve tube. The nitrogen gas helps to improve the ride control of the shock. The gas minimizes the aeration of the hydraulic fluid by compressing the air bubbles and keeping the fluid from foaming. Hydraulic fluid that's foaming can be compressed--fluid that's not aerated does not compress.