Methods and apparatus for suspending vehicles

A pressure-sensitive shock absorber for a vehicle comprising:

• a gas spring having a main gas chamber and a secondary gas chamber, said secondary gas chamber separated from said main gas chamber by a sealed positionally-fixed bulkhead, a volume of said secondary gas chamber not altered by movement of said pressure-sensitive shock absorber, a pressure within said second chamber not altered by said movement of said pressure-sensitive shock absorber until a pressure in said main gas chamber reaches a preset valve cracking pressure;
• a first valve disposed along a first fluid path coupling said main gas chamber and said secondary gas chamber, said first valve having an open position which allows fluid to flow from said main gas chamber to said secondary gas chamber when said pressure in said main gas chamber reaches said preset valve cracking pressure, said first valve having a closed position which prevents said fluid from flowing from said main gas chamber to said secondary gas chamber;
• a user-operable adjustment rod coupled with said first valve, said user-operable adjustment rod configured to control a compression placed on said first valve to select said preset valve cracking pressure;
• and
• a second valve disposed along a second fluid path coupling said main gas chamber and said secondary gas chamber, said second valve having an open position which allows said fluid to flow from said secondary gas chamber to said main gas chamber, said second valve having a closed position which prevents said fluid from flowing from said secondary gas chamber to said main gas chamber, said main gas chamber and said secondary gas chamber operable in combination to increase a range of travel for said pressure-sensitive shock absorber during which said pressure-sensitive shock absorber achieves a linear portion of a spring curve.