The governing concept is skyhook theory: the ideal suspension would keep the vehicle stable as if suspended from an imaginary hook in the sky at a constant altitude, unaffected by weight transfer or road surface irregularities. In practice, an onboard computer calculates an imaginary line of zero vertical acceleration from data supplied by acceleration sensors mounted on the vehicle body. The dynamic elements comprise a linear spring and a linear damper; the vehicle contacts the ground through the spring, and the imaginary line through the damper. Where the damping coefficient reaches a sufficiently high value, the vehicle is effectively fixed to the imaginary line and ceases to shake.
The first active suspension appeared in 1954 with the hydropneumatic suspension developed by Paul Magès at Citroën, applied to the rear wheels of the Citroën Traction Avant 15-6H. In 1955, Citroën extended the system to all four wheels of the Citroën DS. Hydraulic pressure is supplied by a high-pressure radial piston pump; sensors continuously monitor body movement and ride level, and the suspension generates counter-forces within milliseconds. The encased nitrogen compresses instantly, providing six times the compressibility of steel springs. The system also incorporates self-levelling and height-adjustable features, with ride height tied to vehicle speed for improved aerodynamic performance at high speed. Millions of production vehicles have been built using variations on this system.
Colin Chapman developed the concept of computer management of hydraulic suspension in the 1980s to improve cornering in racing cars. Lotus fitted and developed a prototype system on a 1985 Excel with electro-hydraulic active suspension, though it was never offered for sale to the public.
In 1990, Nissan installed a hydraulic supported MacPherson strut-based setup called Full-Active Suspension in the Nissan Q45 and President. The system used a hydraulic oil pump, a hydraulic cylinder, an accumulator, and a damping valve, connecting two independent circuits for the front and rear strut assemblies to continuously balance the car. This system has since been revised and is now called the Hydraulic Body Motion Control System, installed on the Nissan Patrol and Infiniti QX80.
In 1991, Toyota introduced an active suspension on a variant of the Toyota Soarer, using hydraulic struts and four-wheel steering combined with numerous accelerometers to detect acceleration, cornering, and braking forces, compensating in real time by varying steering and suspension pressure individually at each wheel. Fewer than 900 cars of this variant were sold during its five-year production run due to its significantly higher cost.
In 1992, Williams Grand Prix Engineering prepared an active suspension devised by designer-aerodynamicist Frank Dernie for its Formula 1 cars. The resulting cars were successful enough that the Fédération Internationale de l'Automobile banned the technology to reduce the competitive gap between Williams and its rivals.
The 1999 Mercedes-Benz CL-Class (C215) introduced Active Body Control, where high-pressure hydraulic servos are controlled by electronic computing. Vehicles using this system can actively lean into curves to improve occupant comfort.
An active anti-roll bar stiffens under command of the driver or the suspension electronic control unit during hard cornering. The first production car with this technology was the Mitsubishi Mirage Cyborg in 1988.
Electromagnetic active suspension uses linear electromagnetic motors attached to each wheel. It provides extremely fast response and allows regeneration of power consumed by using the motors as generators. Electronically controlled active suspension system (ECASS) technology was patented by the University of Texas Center for Electromechanics in the 1990s and developed by L-3 Electronic Systems for military vehicles; the ECASS-equipped Humvee exceeded all performance specifications for absorbed power, stability, and handling.
Michelin's Active Wheel from 2004 incorporates an in-wheel electrical suspension motor that controls torque distribution, traction, turning manoeuvres, pitch, roll, and suspension damping, alongside a separate in-wheel electric traction motor.
Audi introduced an active electromechanical suspension system in 2017 that drives each wheel individually via an electric motor powered by the 48-volt main electrical system. Each actuator includes gears, a rotary tube with an internal titanium torsion bar, and a lever exerting up to 1,100 N⋅m on the suspension through a coupling rod. A front camera detects road irregularities ahead and predictively adjusts suspension travel before the wheel reaches the disturbance.
Adaptive and semi-active systems can only change the viscous damping coefficient of the shock absorber and do not add energy to the suspension system. Adaptive suspensions offer a slow time response and a limited number of damping values, typically providing selectable modes such as comfort, normal, and sport. Semi-active suspensions modify damping in real time with a response of a few milliseconds across a wide range of damping values, though the control force cannot act in a direction opposite to the current velocity of the suspension. Semi-active suspensions are less expensive to design and consume far less energy than fully active systems.
The most basic semi-active implementation uses a solenoid valve to alter hydraulic flow inside the shock absorber. The first production car with this type was the Toyota Soarer with Toyota Electronic Modulated Suspension in 1983. In 1985, Nissan introduced a version called Super Sonic Suspension incorporating an ultrasonic sensor, with microcomputer-processed data from steering, brakes, throttle, and vehicle speed. This implementation is now used industry-wide by a number of manufacturers and is supplied by Monroe Shock Absorbers under the name CVSAe (Continuously Variable Semi-Active electronic). In 2008 the Nissan GT-R introduced DampTronic, jointly developed by Nissan and Bilstein, offering three driver-selectable settings that also interact with Vehicle Dynamics Control to modify transmission shift points.
Another approach uses magnetorheological dampers, branded as MagneRide. Developed by Delphi Corporation for General Motors, MagneRide first appeared as standard equipment on the Cadillac STS from model year 2002. The damper fluid contains metallic particles whose alignment, and therefore fluid viscosity, is altered by an electromagnet controlled by the onboard computer. Sensors measuring suspension extension, steering angle, and acceleration feed the system, which adjusts stiffness across all four wheels independently within milliseconds.
Input from forward-facing sensors, such as cameras or radar, can scan ahead of the vehicle and predict road conditions, allowing the suspension to adjust proactively before a wheel contacts a disturbance. Audi's 2017 system uses a front camera for this purpose.
The following production milestones are drawn from the corpus:
1954: Citroën Traction Avant 15-6H — self-levelling hydropneumatic suspension on rear wheels
1955: Citroën DS — self-levelling hydropneumatic suspension on all four wheels
1957: Cadillac Eldorado Brougham — self-levelling GM air suspension
1983: Toyota Soarer — world's first electronically controlled suspension (TEMS)
1985: Nissan Super Sonic Suspension introduced on selected models
1987: Mitsubishi Galant (sixth generation) — Active Controlled Suspension
1988: Mitsubishi Mirage Cyborg — first production active anti-roll bar
1990: Infiniti Q45 and Nissan President — Full-Active Suspension
1991: Toyota Soarer (UZZ32) — fully active computer-controlled hydropneumatic suspension with four-wheel steering
1992: Williams Grand Prix Engineering — active suspension on Formula 1 cars
1994: Toyota Celsior — first Skyhook air suspension
1999: Mercedes-Benz C215 — Active Body Control
2002: Cadillac STS — first MagneRide
2004: Michelin Active Wheel
2008: Nissan GT-R — DampTronic
2013: Mercedes-Benz W222 — Magic Body Control with road-surface scanning
2017: Audi — active electromechanical suspension with 48-volt system
2025: Nio ET9 — SkyRide fully active suspension; all Lincoln Motor Company vehicles offered with active suspension
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.