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Only two companies can credibly claim to deliver a magic carpet ride: Citroën and Rolls-Royce.
Rolls-Royce achieves this through an engineering process during which absolutely no expense is spared. Citroën, on the other hand, ingeniously invented a hydropneumatic suspension system it launched during the 1950s and perfected over the following decades. The technology played a key role in the firm’s line-up for over 60 years.
Here we look back at its best days:
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What is Citroën’s hydropneumatic suspension?
First, let’s revisit the basics. Citroën’s hydropneumatic suspension eschews the steel springs found in a vast majority of cars. Each wheel is instead connected to a steel sphere containing nitrogen (which can be compressed) and hydraulic fluid (which can’t be compressed). The sphere also contains a rubber membrane that separates the nitrogen and the fluid.
The older systems are free of electronics. In simple terms, they rely on an engine-driven pump to fill the bottom part of the sphere with pressurized fluid. When the car drives over a bump, the fluid compresses the nitrogen by pushing the membrane up and creates a damping effect.
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Citroën’s first hydropneumatic suspension (1954)
Citroën’s hydropneumatic suspension made its production debut on the rear axle of the 15-6 H (broadly known as the Traction Avant) in 1954. It was the model’s ultimate evolution and it served as a test bed to help engineers put the final touches on the DS. Citroën made approximately 3000 examples of the 15-6 H over a two-year period.
Note: standard 15-6 pictured.
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The DS (1955)
The DS 19 introduced at the 1955 Paris motor show demonstrated the hydropneumatic system’s full potential by offering a smoother ride than luxury cars that cost two or three times more. With forward-thinking design and an innovative suspension, the DS was at least 20 years ahead of its time.
It was also underpowered. In the early 1950s, engineer Walter Becchia designed a water-cooled flat-six engine that would have given the DS the power it deserved. It remained at the prototype stage due to cost constraints and the DS instead arrived on the market with an evolution of the Traction Avant’s 1.9-litre four-cylinder engine.
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Reducing roll
Citroën quickly developed a more advanced hydropneumatic suspension system that eliminated body roll, even under hard cornering. It installed the system in several DS-based prototypes and tested it for several years with the intent of bringing it to the market by the end of the 1960s. Financial problems prevented the technology from reaching production.
The project started again during the early 1990s. Engineers created a sensor-based anti-roll system that came standard on the Xantia Activa introduced in 1994.
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The DS in racing
The hydropneumatic suspension allowed the DS to drive fast over rough terrain in relative comfort. Front-wheel drive gave it better traction than many similarly-sized, rear-wheel drive saloons. It didn’t take long for rally drivers notice the DS’ potential in rallying.
The DS took first in class in the 1956 Monte-Carlo Rally and it won the event outright in 1959. Citroën took home the Constructor’s Title in 1963 and expanded its horizons to African rallies in 1965. The DS won the Monte-Carlo again in 1966 after race organizers contentiously disqualified three Mini Coopers and a Ford Cortina all fitted with illegal lights.
In America, a pair of ID 19s entered the 1958 Crown America 500 NASCAR race in Riverside, California. They took 18th and 19th, respectively, but one won first in class. The ID’s NASCAR career was short-lived, however.
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The line-up grows (1957)
The hydropneumatic suspension cost Citroën a small fortune to develop. Fitting the system to the DS made it considerably more expensive than the Traction Avant it replaced. To avoid alienating loyal buyers, the firm introduced a stripped-down model named ID 19 in 1957, the year the Traction Avant finally retired after a 23-year long production run.
Though it looked a lot like the DS, the ID offered with a less powerful 1.9-litre engine and a shorter list of standard equipment. It also came without power steering or the DS’ hydraulically-actuated clutch.
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The estates (1959)
Citroën announced the estate variants of the ID and the DS in 1958, though it didn’t officially launch the models until October 1959. They were among the best estates on the European market due to their self-levelling suspension and their cavernous interior. They were also less utilitarian than comparable models made by rivals like Simca and Peugeot. In that regard, Citroën had looked to the US for inspiration.
Standard estates had seven seats, including a pair of jump seats that folded into the boot floor when not in use. Citroën also offered variants with front seats only that were commonly used as ambulances, hearses and vans.
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Saving De Gaulle (1962)
French president Charles de Gaulle used a DS as his official car. In 1962, after he controversially granted Algeria independence, 12 gunmen from the Organisation de l’Armée Secrète (a paramilitary organisation vehemently opposed to Algerian independence) opened fire on his cavalcade. 14 of the 187 bullets fired hit the DS, blowing out its front tyres. The driver nonetheless managed to speed away – on wet pavement, no less – and reach his destination safe and sound. In hindsight, the hydropneumatic suspension saved De Gaulle and his wife Yvonne by helping the intrepid driver keep the DS under control.
French law enforcement officials tracked down the participants after a massive manhunt and sent them to trial. The judge decided the men who fired the guns at the president's DS were merely following orders and consequently didn't deserve more than jail time. Three men were given the death penalty, including Jean Bastien-Thiry who was found guilty of organizing the attack. All of them received a presidential pardon sooner or later with the notable exception or Bastien-Thiry, who died by firing squad a week after his trial in 1963.
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The super-Panhard that never was (1965)
Citroën somewhat reluctantly purchased Panhard in 1965. The two firms examined potential areas of collaboration and brought up the possibility of turning the 24 CT into a high-performance grand tourer. Panhard’s air-cooled flat-twin engine couldn’t power such a beast so the coupe received a 2.1-litre four-cylinder from the DS. Citroën also gave the prototype the DS’ hydropneumatic suspension.
In other words, Citroën and Panhard turned the 24 CT into a vague, early preview of the SM. The coupe never reached production, allegedly because Citroën worried about creating internal competition for the SM it already planned on launching. Odds are decision-makers had already made up their mind to deep-six the Panhard brand before the end of 1967, too.
Citroën displays a DS-powered 24 prototype (pictured) in its museum on the outskirts of Paris. The long hood needed to accommodate a four-cylinder engine helps it stand out from the regular-production model.
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Raising Rolls-Royce’s eyebrows (1965)
The DS’ ride quality impressed even Rolls-Royce. The British firm licensed the hydropneumatic suspension system and fitted it to the Silver Shadow it launched in 1965. Early cars came with a self-levelling suspension on both axles. In 1969, Rolls-Royce reverted to a conventional steel set-up on the front axle.
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Spreading the hydropneumatic suspension
Citroën understandably sought economies of scale to offset the cost of developing the hydropneumatic suspension. In 1961, it filled the chasm separating the 2CV from the DS with the Ami 6. Fitting the spring-less suspension wasn’t possible for cost and packaging reasons; the Ami 6 was, for all intents and purposes, a humble 2CV underneath. The firm brought it to the market hastily to buy time.
Behind the scenes, Citroën’s research and development department had already started working on a true mid-range model. It built a prototype (pictured) named C60 that looked like a DS-Ami 6 cross. The design brief called for top-end variants of the car to use the hydropneumatic suspension. Citroën cancelled the project when it became too expensive and started from scratch.
It called the new car Project F. This time, it envisioned base models with a flat-four engine and a steel suspension and more expensive variants with a Wankel engine and a hydropneumatic suspension. The project stopped dead in its tracks when Renault introduced the 16, which shared more than a passing resemblance to the Project F. No one managed to prove the serious allegations of industrial espionage.
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The M35 (1969)
Citroën begrudgingly returned to the drawing board for the second time. The design changed yet again but the firm remained adamant its mid-range model needed to offer either a flat-four or a rotary engine depending on the trim level and its hydropneumatic suspension. It tested the unproven mechanical components by placing a few hand-selected customers behind the wheel of a futuristic-looking prototype named M35.
Power for the coupe came from a single-rotor Wankel engine that shifted through a new four-speed manual transmission. Its hydropneumatic suspension was cobbled together using DS and Ami 8 parts. Citroën planned on making 500 examples of the M35 but ended up building about 267 cars. Each car wore a sticker with its serial number on the wing; Citroën played numerical hopscotch to make it look like 500 were built.
The pilot program ended in 1971, a year after the GS made its world debut, and Citroën tried buying back the M35s still loose on public roads. About a third of the production run survived.
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The GS (1970)
Over a decade in the making, the GS finally saw the light of day in 1970. It beat the NSU-turned-Volkswagen K70 and Citroën’s own SM to earn the coveted European Car of the Year award in 1971. Road testers praised its class-leading comfort and road-handling, two traits at least partially attributable to its hydropneumatic suspension. It became the GSA in 1979 and production continued until 1986.
Note: 1977 model pictured.
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The SM (1970)
Citroën began exploring ways to make a DS-derived coupe during the 1950s. Two-door prototypes raced in various rallies but, by the middle of the 1960s, the firm had decided to develop a standalone model rather than expand the DS line with a coupe. Citroën knew its hydropneumatic suspension would give the car an advantage right off the bat but it didn’t have a suitable engine to power the car. It began developing V6s and V8s in-house during the 1960s but never saw any of the projects through.
Surprisingly, purchasing Maserati was cheaper and easier than developing a V6 engine from scratch. The tie-up produced the SM in 1970. Quick and comfortable, it perfectly embodied the concept of a grand tourer designed to jaunt across Europe at triple-digit speeds.
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The SM in racing
Citroën knew the SM’s pros (its V6 engine and its suspension) and cons (it's roughly 1500kg (3300lb) in weight). It decided to enter the car in the gruelling Morocco Rallye because it was an event in which ride quality and endurance were more important than nimble handling. Citroën had already won it in 1969 and 1970 with a DS (pictured). The SM didn’t disappoint. It took first in 1971, the first year it participated in the race.
The SM’s weight played against it so Citroën entered a short-wheelbase, V6-powered prototype with a DS body in a 1972 race held in Chamonix. After getting a flat tyre, pilot Bjorn Waldegaard raised the suspension to its highest level and drove the remaining two-thirds of the race on three wheels. He nonetheless finished second overall, a feat that would have been impossible in a car with steel springs.
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On the show floor (1972)
Perennially cash-strapped, Citroën opted not to waste time and money on building glitzy concepts for motor shows. It was Bertone that made the first concept fitted with a hydropneumatic suspension. The GS Camargue made its debut at the 1972 Geneva motor show.
For its first collaboration with Citroën, Bertone designer Marcello Gandini started with a GS chassis and turned it into a 2+2 coupe with a wedge-shaped body. The GS Camargue was not approved for production but it led to a partnership between the two companies that created a number of cars including the BX and the XM. Interestingly the Camargue name was also used on a Rolls-Royce made between 1976 and 1986.
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The GS Birotor (1973)
Citroën presented the Birotor as the range-topping variant of the GS. It was the fruit of several years of labour. And while it looked a lot like the more basic GS versions, it received a long list of model-specific parts including a twin-rotor engine similar to the one in NSU’s Ro80, 14-inch wheels under flared arches, an available two-tone paint job and a more luxurious interior. It kept the GS’ hydropneumatic suspension.
Undeniably innovative, the GS Birotor had the misfortune of going on sale during the first oil crisis. It returned abysmal fuel economy – when it ran, which wasn’t always. Citroën made less than 850 examples before pulling the plug on the project. It bought back and promptly destroyed a good chunk of the production run in an attempt to dodge the cost of making spare parts for the model.
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Banned in the USA (1974)
The DS went on sale in the US in 1956 and the ID followed a year later. Both lacked power and equipment in the eyes of American buyers. Their price didn't help their cause, either. In 1968, the DS 21 started at $3798 (about $27,500 in 2018). For about the same amount of money, buyers could drive home in a Buick Wildcat Custom with A/C, power-operated seats, a 360hp V8 engine and an automatic transmission -- and without a wacky suspension the local mechanic wouldn't touch with a 10-foot pole. The posh Pallas trim entered Cadillac territory. The base ID 19 cost $2898 ($21,000 in 2018), about as much as an entry-level, straight-six-powered Chevrolet Impala.
Citroën genuinely hoped to expand its American presence with the GS. It even sent its dealers a handful of US-spec cars (fitted with sealed-beam headlights) to prepare for the launch. However, it cancelled those plans when the National Highway Traffic Safety Administration (NHTSA) banned companies from selling cars with an adjustable ride height on the grounds of safety concerns. The rule kept Citroën’s bigger models out. Its smaller models were ill-suited to the American market so, with nothing else to Americanise on the horizon, officials decided to leave the US altogether in 1974.
In 2017, parent company Groupe PSA confirmed it will return to the US during the 2020s. It’s too early to tell precisely where Citroën stands in the company’s comeback plans. Inside sources speculate Peugeot and Opel, not Citroën, will spearhead the American offensive but the roadmap could change.
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The CX (1974)
Getting regulated out of the US was the least of Citroën’s problems.
It hoped to replace the DS with a state-of-the-art saloon. Base models would get a four-cylinder but period reports indicate the flagship was set to use a triple-rotor Wankel rated at approximately 160hp. Rising fuel prices and reliability issues forced Citroën to cancel those plans a few short months before the start of production. The SM’s V6 was too tight of a fit. It was far too late to re-design the engine bay. Delaying the launch was ruled out, too.
The international press discovered the CX in August 1974 with a 2.2-litre four as its top engine. Luckily, the hydropneumatic suspension helped save the day by delivering world-class comfort and handling nearly every road tester praised.
Note: 1983 model pictured.
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The Maserati Quattroporte II (1974)
Citroën had grandiose plans for Maserati. It began developing a successor to the Quattroporte but, without the necessary funds, settled for building it using components borrowed from the SM. This route led to a saloon with front-wheel drive, a V6 engine and a hydropneumatic suspension. In other words, Maserati had created the opposite of the original Quattroporte.
Maserati made 13 examples of the Quattroporte II, including one prototype. It’s remembered as the brand’s first, last and only front-wheel drive car.
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Peugeot steps in (1976)
Citroën again fell in dire financial straits during the 1970s. It wasted a colossal amount of money on purchasing and closing down Panhard, acquiring Maserati, the two aborted projects leading up to the GS, the Comotor joint-venture with NSU, an abstruse attempt at manufacturing a helicopter and unsuccessful cars like the SM. It looked like the firm’s days were numbered so, in 1976, the French government asked Peugeot to save it. There were too many jobs at stake to let it sink.
Peugeot, some worried, would dilute Citroën by turning the quirkiness down a few notches. The merger brought a certain degree of standardisation in the form of the Visa and the LN but Peugeot permitted Citroën to continue using its hydropneumatic suspension when it replaced the GS with the BX (pictured). The XM and the Xantia received more advanced systems that incorporated electronics.
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The end of the spheres (2017)
Citroën stopped producing its hydropneumatic suspension when it built the last European-spec C5 in June 2017. Brand purists howled when they heard the news but, sadly, the move made sense. The system adds cost and weight in an era when automakers are under a tremendous amount of pressure to build lighter cars while reducing costs. Advancements in electronic suspension technology rendered the hydraulic system obsolete, according to company officials.
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What’s next? (2018 and beyond)
Citroën developed a hydraulic suspension system named Progressive Hydraulic Cushions it introduced on the updated C4 Cactus. The set-up now consists of hydraulic stops that gradually slow down the suspension’s travel. They eliminate rebound by dissipating the energy they absorb instead of channelling it back into the shock absorbers.
Autocar tested the Progressive Hydraulic Cushion technology in the C4 Cactus. We concluded it ‘soaks most imperfections in the road up without breaking a sweat’ while maintaining a composed ride. Citroën told us it plans on using its new suspension in all of its models from the C1 one up.
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