60 years of SL: The design of the Mercedes-Benz SL-Class

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The Mercedes-Benz SL-Class has always set the highest design standards in all model series. Both outside and in, the vehicles are as if hewn from the same block and most show their credentials as future classics during their own production lifetime. The word “design”, also adopted in German for the creative process from English usage, incorporates the concept of technical design, of engineering in the English sense of the word. What is commonly seen to have a double meaning today has special and far-reaching significance in the case of the SL, since from its inception back in 1952, the history of SL design has been fuelled in particular by the interaction between aesthetic features and the relevant contemporary constructional requirements on the product.

The Mercedes-Benz 300 SL (W 194) racing sports car, 1952

The demand for two seats and high efficiency through very low wind resistance clearly determined the design of the 300 SL racing sports car (W 194 series). The shape created in the process optimally met the principal demand on body design expressed in the phrase “form follows function”. For example, the fact that the six-cylinder engine was canted 50 degrees to the left was due to the low-slung bonnet and small frontal area.

The special thing about the body of the W 194 is that it took aesthetic factors into account to a high degree – in great contrast to many competitors of the day – even though this was not the main concern in designing it. Several decades later, the W 194 continues to impress the beholder with what many people still regard as beautiful proportions. As was customary in the period in which it was built, this body was developed by coachwork engineers. Designers as we know them today did not yet exist at Mercedes-Benz.

Wind tunnel measurements on historic vehicles in January 2012 confirmed the targets of the vehicles’ engineers. The 300 SL racing sports car from the W 194 series and a direct contemporary, a 300 S (W 188), a sporty luxurious touring car, were measured, along with a 300 SL production sports car from the W 198 I series, which evolved from the W 194. The figures shown below were obtained with an airflow speed of 200 km/h to make them comparable with measurements normally made today.

The W 194 attained a drag coefficient of cd = 0.38 – a very good value for those days, as the comparison with the W 188 (cd = 0.48) shows. The body of the W 194 was optimised for low wind resistance, and this shows in the overall design of the exterior, whereas the W 188 was designed in line with criteria more typical of the pre-war period. The production sports car of the W 198 series achieved a cd value of 0.40.

The Mercedes-Benz 300 SL (W 198 I), 1954 to 1957

Further factors now found consideration in the construction of the Mercedes-Benz 300 SL (W 198 I), whose frame and chassis engineering derived from the 300 SL racing sports car (W 194). The demands on car bodies were becoming increasingly complex. In addition to purely functional and aerodynamic criteria, a growing importance was attached to aesthetic demands. Together with superior performance, customers of the target group expected elegance, exclusivity, prestige and the appearance of prosperity.

On the basis of the racing sports car, Friedrich Geiger, then head of the styling department, developed a shape which neither Mercedes-Benz nor any other manufacturer had in its programme at the time. With his artistic sense of style, Geiger sculpted a body which, with inimitable elegance, gave visible expression to the abilities of this high-performance sports car through the muscular design of the car’s body. The two powerdomes on the bonnet were invigorating elements. The dome on the right was determined by the position of the intake pipe. For reasons of symmetry the bonnet was given two domes.

Geiger developed an entirely new face for the W 198, one completely different from that of the W 194 racing sports car, and one that, as a second “Mercedes face”, would be typical for decades to come both for the SL and – something nobody expected – for the design of the front ends of Mercedes-Benz buses and commercial vehicles. The characteristic feature is the ensemble positioned in front of the large radiator opening and consisting of a centrally arranged Mercedes star flanked on either side by horizontal chrome inserts as design elements.

Geiger made very clever use of “eyebrows” fitted over the wheel arches to “stretch” the curvaceous body.

The gullwing doors did not give easy access, but they certainly helped give the car its air of exclusivity and are the hallmark of the Coupé to this day. Geiger adopted them from the W 194. Only the bumpers, required by registration regulations, diminished the harmonious overall impression of the silhouette. Bruno Sacco, the later head of design, once said in an interview he felt it was a strategic mistake in the 1950s to replace the gullwing Coupé with the Roadster. The high regard shown today for the Gullwing, the 300 SL (W 198 I), proves Sacco right. For good reason it was voted sports car of the century in 1999. It established the legend of the SL and has retained its fascination as a design icon over the decades. Admittedly though, its successor, the Roadster, remains the super sports car with greater everyday practicality.

The Mercedes-Benz 300 SL Roadster (W 198 II), 1957 to 1963

Just a few months after the presentation of the production Gullwing in February 1954, Friedrich Geiger made preliminary sketches for the open-top 300 SL, urgently requested by US importer Max Hoffman. In 1957, the 300 SL Roadster (W 198 II) was finally able to fulfil the wishes of the rich and beautiful for unhindered enjoyment of the sun and fresh air. The chief design feature was the lamp unit recessed in the front wing, with indicators, main headlamp and fog lamp combined under one lens. Compared with the Gullwing and its circular headlamps, these lamp units give the car a more powerful look. Geiger obtained the longitudinal dynamics in the side view by using swage lines that ran the length of the doors. He did not change the basic body shape. Available later, a removable hardtop with a panoramic rear window extending far around the sides particularly enhanced the balance of the design. When the roadster soft-top was folded down, it was stored under a cover smoothly integrated into the body lines. From the side the car looked all of a piece. Owing to its simple handling, Geiger’s soft-top construction was described at the time as the fastest manually operated soft-top in the world.

The 300 SL Roadster successfully met the aspiration of Mercedes-Benz to return to building absolutely world-class, sporty roadsters after the Second World War.

The Mercedes-Benz 190 SL (W 121 I), 1955 to 1963

The Mercedes-Benz 190 SL (W 121 I) was not the favourite of its initiator, Max Hoffman. But Hoffman quickly recognised that the 190 SL was the most important vehicle for him in the North American market. Following its successful unveiling at the show in New York, both the engineering of the vehicle and its styling were subjected to extensive revision.

Under the direction of Walter Häcker, the body was redesigned prior to production readiness. The front end got a trapezoidal radiator opening which imitated the 300 SL design; in contrast to the vehicle shown in New York, the upper edge protruded beyond the lower edge and, in addition, was slightly wedge-shaped. The bonnet was dominated by a centrally positioned powerdome, which created room for the vertically installed four-cylinder engine underneath. The front view of the 190 SL was strongly reminiscent of the 300 SL – a feature that has won the vehicle many friends through today. Optically, as with the 300 SL, the sides were stretched by “eyebrows” positioned over both wheel arches. The omission of the distinct suggestion of rear wings – in its original form these made the car appear unnecessarily stocky – lent the body additional elegance. Visually, the rear wings, or the merest hint of these in the production version, appeared to lengthen the body and give it a certain lightness when viewed from the side.

The changes made by Häcker proved a resounding success. With an unusual display of euphoria, the Swiss “Automobil Revue” passed judgment on the design of the 190 SL in November 1956: “With its elegant design, the 190 SL generally is considered to be the finest creation from the house Daimler-Benz.” In “Motor Revue”, No. 16, 1955, Heinz-Ulrich Wieselmann observed: “Because of its really handsome exterior, everywhere the 190 SL appears it draws attention. With the top folded down it is downright beautiful.”

In 1959, when the hardtop of the 190 SL was given a rear window that curved around the sides exactly like that of the 300 SL Roadster, the 190 SL then truly looked like the little brother of the high-performance roadster. Although this was just a case of appearance, it did nothing to harm the vehicle’s reputation.

The Mercedes-Benz SL of the W 113 series, 1963 to 1971

The creation of the W 113 series under Friedrich Geiger marked a paradigm change in SL design; not because of the Pagoda roof, but in spite of it. The break with curves and arches symbolising organic forms such as muscle strands meant SL design for the W 113 model series called for a new perspective. The designers of those years were called upon to create more useful space, while retaining the basic area of the predecessor, the W 121 I. The result was a body with characteristic smooth surfaces, which refrained from extensive use of trim elements. Only the flared wheel arches and tyres that completely filled them conveyed a sense of power and dynamism. In the area of the rear wings, a delicate, barely perceptible shoulder echoed the tailfin era that was coming to an end. The angular end of the rear wing, in conjunction with the boot lid that followed it in silhouette, resulted in useful load compartment capacity. Owing to the low waistline and large glazed surfaces, even with the top closed the car gave the impression of lightness and airiness, making one forget the feeling of confinement which many convertibles and sports cars give their occupants.
A fillet running from the headlamp unit through to the rear end, in combination with sills drawn inwards at the bottom and two rubber-capped chrome strips in the lower area of the doors, gives the compact two-seater a stretched appearance. This avoids the impression of tedious two-dimensionality in the side view.

The front end is dominated by a radiator opening which is wider than in the previous model and integrates the Mercedes star and the two flanking chrome inserts. The now almost rectangular headlamp units form the outer boundary. This is the first car in the SL design story that displays a vertical homogeneity of traditionally evolved style elements. But there were also critics for whom the even wider face of the W 113 model series, though effective, was at the same time a formal exaggeration. The chrome frame on the arch bordering the top of the grille was made thicker and prominently emphasised the expressive power of the face of the SL in the W 113 series.

The curvature of the bonnet with its striking powerdome contrasted with the otherwise level surface structure of the body and resulted from the installation of a vertical in-line six-cylinder engine.

A special feature of the W 113 series, and one that is often overestimated in terms of its significance for design, was the concave hardtop, spontaneously dubbed “il pagoda” by the Italians – an expression which over the decades has become established as a synonym for the entire model series. The starting point for this hardtop shape came from the idea of safety pioneer Béla Barényi to create additional carrying space on the roof of a passenger car. To this end Barényi conducted extensive tests on saloons of various model series. But to put this idea into practice for the first time in a sports car, of all things, did not meet with unanimous approval. The head of development, Hans Scherenberg, regarded the Pagoda roof as a signature of the vehicle – it served no functional purpose as far as driving was concerned. And his successor, Werner Breitschwerdt, pointed out another aspect, rooted in the personality of Karl Wilfert, head of body development in Sindelfingen: “Imagine a modern sculpture – people stand around and argue about it until they are blue in the face. That was to Wilfert’s taste. The fact that one had to discuss it – that appealed to Wilfert.” And Bruno Sacco, successor to Geiger (a collaborator of Barényi’s for many years) as head of design, also went on record on the topic of the Pagoda roof: “Realising this Pagoda roof in a sports car was the most off-beat thing one could do.” The editor in chief of “auto motor und sport”, Reinhard Seiffert, voiced this opinion in the issue 21 of 1963 in his test report on the 230 SL: “The purpose can only be to achieve a stylish effect. Wilfert argues that it permits high side windows and thus comfortable access, but that would also have been the case had the roof bulged upwards rather than downwards. On the other hand, the cd value (Daimler-Benz keeps very quiet about that) certainly would have been better.”

The design was developed under the direction of Friedrich Geiger and followed the functional trend of passenger cars of the period like the luxury saloons of the W 108/W 109 series or the “Stroke Eight” model series W 114/W 115. The hardtop design was realised by Paul Bracq. Today the “Pagoda” is still seen as a harmonious design – as Friedrich Geiger’s original and lifelong aspiration, it is an achievement confirmed both by Werner Breitschwerdt and his successor Bruno Sacco.

The design of the hardtop with concave roofline also demonstrated the increasing influence of design elements on contemporary marketing considerations. But in this respect, the Pagoda roof itself proved more or less inconsequential, since when the fabric top was in use, all arguments for and against the Pagoda roof were rendered superfluous.

The Mercedes-Benz SL of the R 107 series, 1971 to 1989

The design of the R 107 series SL was influenced by an abundance of internal and external requirements. Internal requirements included the call for more powerful V8 engines and the planned installation of rotary piston engines. Sufficient installation space had to be provided especially to fit rotary piston engines with their high centre output shaft. A further point to take into account were the stiffer demands on crash behaviour, which meant the installed position of the fuel tank was moved from underneath the boot to an impact-protected area above the rear axle. These measures had a significant impact on the proportions of the overall package.

A noticeable difference from the predecessor was the strong emphasis on horizontal design elements. In keeping with the brand philosophy of vertical homogeneity, the front end again showed a classic SL face. But its expanse was distinctly reduced through the use of horizontal headlamp elements. Owing to the less strongly arched lines, the upper edge of the chrome-plated grille frame appeared much tauter than in the previous model series W 113. The glass of the indicators bordering the headlamp units flowed over into the lines of the car’s side, satisfying legal requirements specifying that turn indicators also had to be visible from the side. All in all, the waistline was higher than in the previous model. The larger side surfaces that resulted were relieved by placing increased emphasis on horizontal elements. These included rub strips connecting the ends of the front and rear bumpers, which were drawn round into the lines of the side, as well as wave-like shapes in the wings and doors underneath the rubber strips and a swage line connecting the tips of the front and rear turn indicators.

A special feature that really should have earned the R 107 the honorary title “Pagoda” was the homogeneity in design of the hardtop and boot lid, both of which curved slightly inwards. Compared with the previous model, the rear end appeared much fuller in its design. Relocation of the fuel tank and the enlarged boot capacity engendered changed rear proportions. The dominant horizontal design element at the rear were two large rectangular taillights with their ribbed surfaces. The horizontal element was further emphasised by the continuous bumper, the boot lid handle and the chrome strip that completes the boot lid.

The rear quarter window of the hardtop did not follow the window-level upper edge of the body but was drawn slightly upwards to hide the soft-top compartment cover, which lay flat but in a raised position.

The design of the R 107 was only marginally changed during the 18 years in which it was built. The changes concerned mainly the post-1985 front-end design. Owing to the use of more powerful engines with higher cooling air requirements, spoilers were fitted there to improve the cooling air supply.

Also starting in 1985, only aluminium wheels with a diameter of 15 inches and a smoother design were used after the facelift. These enabled fitting larger brakes.

The reactions of the press to the new SL were critical. Belgian journalist Paul Frère had this to say in “Motor Revue” in 1971: “In the C 111 Daimler-Benz showed what it is capable of offering. After this, I would have expected more in many areas. In purely visual terms, the car is reminiscent of its predecessor.” And Reinhard Seifert observed in his test report on the 350 SL in “auto motor und sport”, No. 20, 1971: “Once cannot talk of progress in body styling in this case. The 350 SL can hardly be described as more beautiful than the more smoothly and cleanly designed 280 SL. The pronounced arch of the bonnet is irritating even from inside the car. Since the waistline is very high and rises towards the rear, visibility can be described as satisfactory at best. The interior seems more confined and darker than one is to expect from modern sports cars.”

Despite all the criticism, the R 107 series was to have the longest production run – 18 years – of any passenger car series in company history, the G-Class excepted.

The Mercedes-Benz SL of the R 129 series, 1989 to 2001

When the R 107 SL series was replaced by the R 129 series after a production span of 18 years, a murmur passed through the world of admirers of beautiful automobiles. An SL of such simplicity, with clean, elegant lines, created a new point of reference in the Mercedes-Benz SL story.
SL design attained a new formal quality not only under the direction of Bruno Sacco, but through his active involvement. Under Sacco’s patronage, an SL was created in which body design combined utmost simplicity of expression with smoothly flowing lines to compose a work of great formal harmony. Powerfully swept curves in the style of muscle cars were not to be found in the R 129.

Sacco’s statement that the R 129 series impressed through simplicity of expression is confirmed by inspection of the car. The most sparing use of chrome trim and the omission of chrome inserts on the radiator grille next to the star make the star the sole focus in a face with a straightforward brand message bare of provocative dominance. The elimination of superfluous decorative elements underscored the impression of elegance owed to the unsurpassed simplicity of the body’s lines. A body as a work of art – only rarely was design accorded such recognition. The body’s design met with great approval across the board.

The Swiss journal “Automobil Revue” made interesting observations in its first test report on the R 129 in issue 41 of 1989, quoting the voice of the people: “It was a star at the Geneva Motor Show this spring, and it is most definitely a star in normal road traffic. Wherever one goes in the car, it is the object of unqualified admiration. Whether younger or older, female or male – with very few exceptions everyone feels the new showpiece from Stuttgart is brilliantly and impeccably bodied.”
In 1990, Mercedes-Benz received the Car Design Award for the R 129. The jury, comprised of two US journalists and one each from Japan, Germany, France, Italy, Spain, Britain, Sweden, the Netherlands and Switzerland, as well as a representative of the city of Turin and one from the Piedmont region/Italy, voted the R 129 its first choice by a large margin, giving as its reason: “In the Mercedes-Benz 300-500 SL the ensemble of safety innovations, exemplary ergonomic solutions, and stringent adherence to the traditional design culture of the manufacturer’s brand is convincing. The new SL embodies the most valuable elements of state-of-the-art industrial design, without compromising the flair that distinguishes every sports convertible.”

The Mercedes-Benz SL of the R 230 series, 2001 to 2011

The R 230 series introduced in 2001, in its first version, built until 2008, impressed through the resurgent emotionality of organically influenced arched surfaces. The rediscovered and re-implemented curves were intended to give visual form to the impression of power and dynamism that found its counterpart in models with more powerful engines.

The front design was dominated by twin headlamps, which merged into one another in a horizontal eight; their layout continued three-dimensionally towards the rear, ending in the wing and bonnet. In the upper part of the radiator opening, the centrally arranged Mercedes star held the eye, but the star’s central function was partly relativised by glossy horizontal louvres. The increased space requirements at the rear on account of the folding steel roof, used for the first time in an SL, and increased boot capacity – the accommodation of two golf bags was one development target – resulted in a longer wheelbase. The optical heaviness of the larger mass was skilfully covered up by the curves and arches of the rear end.

In the 2008 facelift, the front end was thoroughly reworked. With the centrally arranged Mercedes star again flanked by two chrome-plated horizontal louvres, as in the early days of the SL, and with the two powerdomes on the bonnet, it definitely conjured up memories of the original SL of 1954, whose dominant appearance symbolised unreserved power and superiority.

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