Citroën SM
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The Citroën SM was a high performance coupé produced by the French manufacturer Citroën between 1970 and 1975. The SM placed third in the 1971 European Car of the Year contest, trailing its stablemate Citroën GS, and won the 1972 Motor Trend Car of the Year award in the US in 1972.
History
In 1961, Citroën began work on 'Project S' - a sports variant of the revolutionary Citroën DS. As was customary for the firm, many running concept vehicles were developed, increasingly complex and upmarket from the DS - eventually becoming a halo vehicle for the brand. Citroën purchased Maserati in 1968 with the intention of harnessing Maserati's high performance engine technology to produce a true Gran Turismo car, combining the sophisticated Citroën suspension with a Maserati V6 engine.
The result was the Citroën S first shown at the Geneva Motor Show in March 1970. It finally went on sale in France in September of that year. All produced were left-hand-drive, although some RHD conversions were done in the UK, and also Australia.
The origin of the model name 'SM' is not clear. The 'S' likely derives from the Project 'S' designation, the aim of which was to produce what is essentially a sports variant of the Citroen DS, and the 'M' perhaps refers to Maserati, hence SM is often assumed to stand for 'Sports Maserati', but others have suggested it is short for 'Sa Majesté' (Her Majesty in French), which aligns with the common DS model's nickname 'La déesse' (The Goddess).
The SM was Citroën's flagship vehicle, competing with other high performance GTs of the time from manufacturers such as Jaguar, Lotus, Ferrari, Aston Martin, Alfa Romeo and Porsche. It was also Citroën's way of demonstrating just how much power and performance could be accommodated in a front-wheel drive design.
The SM innovated a new type of variable assist power steering that has since spread throughout the vehicle population. It allowed great assistance to the motorist while parking, but little assistance at motorway speeds. The steering actually had the same "assist" at all speeds - the steering was hydraulically locked against steering movement of the wheels from the road ("feedback") up to the capacity of the unit. Hitting a pothole at high speed would not turn the steering wheel in the driver's hands! The reduction in 'assist' was achieved by a piston/roller pushing on a heart shaped cam geared to the steering shaft (hence the one turn to full lock), which was fed with system pressure so that as its pressure rose with increasing road speed, the steering assistance seemingly reduced and the steering centering effort rose. However, full steering wheel turning was available at all speeds, though considerable force was necessary to turn the steering wheel at high road speed. Enough pressure was admitted to the centering unit to return the wheels to the straight ahead position when the car was not moving. The centering pressure was regulated by a flyweight centrifugal governor driven by the pinion (secondary) shaft of the manual gearbox and by a proportioning valve connected to the fluid pressure in the automatic gearbox, which pressure was proportional to the speed of the output shaft. The pressure increased all the way to 120 MPH, and a subsidiary function of this feed was to turn off the air conditioning fans above 50KPH.
Contemporary automotive journalists were most effusive about the SM's dynamic qualities, which were unlike anything they had experienced prior. The SM provided a combination of comfort, sharp handling, and high performance not available in any other car at the time. Popular Science noted that the SM had the shortest stopping distance of any car they had tested. To this day this stopping distance remains outstanding.
The SM won its first competitive outing, the grueling 1971 Rallye du Maroc.
Unfortunately, the SM did not find a sufficient customer base in the European GT market, but much of the SM's technology was carried forward to the successful Citroën CX, launched in 1974 - the DIRAVI steering being the most obvious example. The same basic engine in enlarged 3.0 L form (some in Italy had 2 litre) was used in Maserati's own Merak which, together with Maserati's Khamsin and Bora, used Citroën's high pressure hydraulics for some functions, and the Citroën gearbox in the Merak, during the Citroën-Maserati alliance.
Styling
The look of the car, although easily identifiable as Citroën, is quite distinct, with a shape that even today looks futuristic. Designed in-house by Citroën's chief designer Robert Opron, the SM bears a vague family resemblance to the DS, especially in retaining the latter's rear wheel spats. Seen from above though, the SM resembles a teardrop, with a wide front track tapering to a narrower rear track.
Many of the details reflect Opron's American background, notably the vestiges of 'fins' at the rear. Opron worked on aircraft body design and aerodynamics while in the USA, and the SM benefited from this experience. It was unusually aerodynamic for its era, with a very low drag coefficient of 0.26[1]. The SM was one of the first production cars to benefit from extensive wind tunnel testing during its design phase, and as a result aerodynamic efficiency influenced the final design of many details including the shape of the side mirrors, the method of windshield sealing, and the underbelly of the car which featured active aerodynamics, effectively sucking the car to the road at high speed.
European critics marveled at the resulting ability to travel for hours at 200 km/h (120 mph) in comfort and with impressive fuel economy on the large 90 litre (20 US gal; 17 Imp. gal.) fuel tank.
With its distinctly Art Deco influence, the interior styling of the SM is as dramatic as the exterior. The small oval steering wheel is matched by oval gauges. The manual shift lever 'boot' is a highly stylized chrome gate. The seats are highly adjustable buckets with centre padding composed of many individual 'rolls'. High quality materials are used throughout. The bonnet is aircraft grade aluminum, while the external bright work is stainless steel, rather than ‘cheaper’ chrome (except for "plastichrome" "SM" trim at the rear base of the rain gutter).
The SM's design is timeless; the car was even used in a 1999 television advertisement for British Petroleum of Spain, where 'a futuristic car was required'. It placed eleventh on Automobile Magazine's 2005 "100 Coolest Cars" listing.
In 1970, it was a car of the future and the fastest front-wheel drive car to be made, with a factory quoted top speed of 220 km/h (135 mph), and independent tests achieving as much as 235 km/h (145 mph). It was an example of the car as a symbol of optimism and progressive technology, similar to the SM's contemporary, the Concorde aircraft. The true distinction in speed of the SM is its ability to maintain 200 km/h (125 mph) from one fuel stop to the next. Many other cars will go faster for a dash, but most will not withstand long periods at such speed.
Technical Innovations
The SM combines many unusual and innovative features, some of which are only just becoming commonplace on cars of today. It borrows heavily from the innovations introduced on the DS, by including hydro-pneumatic (oleopneumatic) self-leveling suspension, and self-leveling lights that swiveled with the steering (except in the USA where such was illegal).
The steering is self-centering and fully-powered (as opposed to hydraulically assisted). This feature allows the front wheels to run near-zero caster, and means that there is no camber change as lock is applied, and also ensures that the maximum amount of tire area is in contact with the road at all times. The system also adjusts the hydraulic pressure on the steering centering cam according to vehicle speed so that the amount of steering feel remained almost constant at any speed, counteracting the tendency of manual and ordinary power assisted steering to feel light at high speed. Thus the car turns easily at low speed, emphasized by high gearing given two turns lock-lock, and relatively more effort is required at higher speed. Many contemporary reviewers remarked that this system would take at least 50 miles of driving (roughly 80 km) to become familiar, but once the driver is accustomed to the system traditional steering feels old-fashioned[2].
The wiper mechanism is 'sensitive' to rain, while the steering column is adjustable in both height and reach.
The braking system, adapted from the DS, employs disk brakes at all four corners (the D has drums at the rear), with the front brakes being inboard, and cooled via large ducts on the front underside of the car. The hydraulic braking pressure front to rear balance is self-adjusting according to the weight in the rear of the car.
Standard wheels are steel with stainless trims, but a factory option was available for lightweight wheels made of composites.
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Citroen SM Stockholm