Height adjustable suspension is a feature of certain automobile suspension (vehicle) systems that allow the motorist to vary the ride height or ground clearance. Such a feature requires fairly sophisticated engineering.
Citroën CX in high position.
Height adjustment is most often achieved by air or oil compression used for the "springs" of the vehicle - when the pressure is varied - the vehicle body rises or lowers.
Height adjustable suspension from 1954 - also high position.
The first instance of a production vehicle with adjustable suspension was on the 1954 Citroën 15CVH. This vehicled featured a self-leveling, height adjustable hydropneumatic suspension. Since this time, these systems have appeared continuously on Citroën models, including the DS and CX.
Height adjustable suspension was banned in the United States from 1974 to 1981, due to the stringent interpretation of passenger vehicle bumper height regulations by the U.S. government agency NHTSA.
Many Modern SUVs use height adjustability as part of active suspension systems to improve the vehicle's versatility on and off road. The Range Rover offered this feature from 1993. New models of the Ford Expedition have a computer-controlled system designed for convenience, which lowers automatically when the doors are unlocked by remote, returns to normal height when the vehicle is started, and (on 4-wheel-drive models), raises when the 4x4 system is engaged.
Some sports cars use these systems to improve the vehicle's handling by lowering the vehicle's height during higher speeds - a current example being the Mercedes-Benz Active Body Control system.
Height adjustable air suspensions are also equipped on "Low-floor" city buses or "Kneeling Buses". This allows the floor to be lowered at a bus stop, to allow handicapped passengers to board more easily.
Aftermarket height adjustable suspension installed on 1964 Chevrolet Impala lowrider.
Adjustable suspensions have become intrinsically associated with lowrider vehicles. The popular image of these vehicles is of one "hopping" on its suspension, or sitting with one wheel completely off the ground.
These systems were initially adapted from the hydraulic pistons, valves and pumps used to adjust the flaps on aircraft. Today however, many aftermarket companies produce parts and equipment specifically designed for lowriders.
In recent years "air bag" systems (not to be confused with the air bag safety device) have been rapidly gaining popularity among car customizers. These air suspension systems use heavy duty custom rubber "bags" to replace the stock shocks and springs, with either a compressor or tank of compressed gas used to raise and lower the vehicle at will.
History of aftermarket systems
Ron Aguirre is commonly accepted as the first person to create a custom car with hydraulically adjustable suspension. In 1959 he scavenged the Pesco pumps and valves from a B-52 Bomber and adapted them to the front suspension of his X-Sonic bubble-topped custom Corvette, allowing him to change the height of the car with a switch on the dashboard.
Traditional height adjustable suspension is controlled by the driver manually. Certain modern layouts allow electronics alone to make this decision without the driver's control, especially if the car lowers at high speed.