Well-weighed development: the first Mercedes-Benz SL models in the 1950s
Stuttgart
Mar 16, 2012
  • 300 SL (W 194): With serial components developed for racing
  • 300 SL (W 198) and 190 SL (W 121) followed as production sports cars
Stuttgart – The Mercedes-Benz 300 SL (W 194 series) racing sports car came as an overwhelming surprise: although people had hoped for a car like this from Mercedes-Benz during the post-war period, it still left the world speechless when it was presented in March 1952. That same year, the 300 SL enjoyed enormous success at all the major international racing sports car events. Despite its surprise effect, however, the 300 SL racing sports car was not a product of chance, but the result of thorough engineering work. From it emerged the W 198 series production sports car with the identical model designation, 300 SL. The Mercedes-Benz 190 SL (W 121) was developed in parallel. The brand showed both cars in February 1954 at the International Motor Sports Show in New York and received a tremendously positive response.
Development of the 300 SL racing sports car (W 194)
In 1951, the then chairman of Daimler-Benz AG, Wilhelm Haspel, had his experts keep a watchful eye on the international motor sport scene. To Haspel, involvement in motor sports was key to restoring added lustre to the company’s global reputation once again. He was confirmed in this view by the many enquiries he received from 1946 onwards, especially from English-speaking countries, asking when Daimler-Benz intended to return to international racing.
On the other hand, involvement in grand prix racing was rendered relatively uninteresting by the decision of the FIA (Féderation Internationale de l’Automobile) to introduce a new racing car formula from 1954 (2.5-litre displacement for naturally aspirated engines or 0.75-litre displacement for supercharged engines). The term remaining for the 1.5-litre formula still in force hardly justified the development of a completely new racing car under that formula – although the company did look into the possibility in a project designated W 195. This did not get beyond the planning stage, however. And although still in existence, the pre-war W 165 was no longer competitive. So to comply with Haspel’s demands, the only course of action was to engage in sports car racing.
Haspel saw a clear opportunity here and his basis were the new 220 and 300 passenger car models with their new OHC engines introduced in the spring of 1951 at the International Motor Show (IAA) in Frankfurt am Main. For it had not gone unnoticed in Untertürkheim that Jaguar had achieved success in international racing with the XK 120 sports car developed using components of its 3.5-litre Mark VII saloon.
It had been decided that the representational 300 Saloon (W 186 series) would be joined by a sporty two-seater. This was developed almost in parallel and made its debut as the 300 S (W 188) at the Paris Motor Show in autumn 1951. Haspel toyed with the idea of putting it to sports use. In June 1951, he asked his chief development engineer Fritz Nallinger about the prospects of success. Nallinger’s unequivocal response was that there was little hope of success in racing using a passenger car chassis; these vehicles were too heavy and, at best, could only be used as touring cars. But as Haspel was dead set on involvement in motor sport, the project to develop a racing sports car was pursued further. The result was the Mercedes-Benz 300 SL (W 194).
Its M 194 engine was derived from the power plant of the 300, the M 186, with an inclined separation plane between cylinder head and engine block, overhead camshaft, large inlet valves, combustion chamber in piston and engine block, a displacement of 3 litres, and 115 hp (85 kW). For use in the racing car the engineers increased the engine’s output to around 170 hp (125 kW). The sports engine differed from those installed in the Saloon and Coupé not only in terms of output; it was also mounted differently, canted at 50 degrees to the left, and featured a dry-sump lubrication system, which enabled a lower installation height owing to the lack of oil sump.
The engine and transmission of the maturing W 194 offered few opportunities for weight savings. The same was true of the heavy steel axles borrowed from the 300 model. That left only the frame and the outer skin for any possible weight reductions. Another option for enhancing competitiveness was to make the body as aerodynamic as possible. Rudolf Uhlenhaut, at that time head of passenger car testing at Daimler-Benz, once again returned to his concept for a lightweight tubular frame, an idea he had worked on some years earlier. The designers then carried the concept forward to its logical conclusion, creating an extremely lightweight, torsionally rigid spaceframe made up of slender tubes welded into triangles, the tubular elements of which were subjected only to tension and compression forces. In torsion tests, the spaceframe proved stiffer than the chassis of the pre-war W 154 formula racing car, which had marked a great step forward in its day. The entire frame weighed just 50 kilograms and formed the backbone of the W 194. The success in weight reduction was dramatic: a 300 S tipped the scales at around 1780 kilograms, whereas the 300 SL (W 194) weighed in at only 1100 kilograms.
In addition to cutting weight to improve acceleration, Uhlenhaut also sought to cut frontal resistance to optimise top speed. To achieve this he canted the relatively tall, in-line, six-cylinder engine at 50 degrees to the left, additionally reducing the height by using a dry-sump lubrication system, which did away with the need for an oil sump as an oil reservoir. These measures gave the car a very low-slung bonnet.
The body of this first SL anticipated a number of features of later production sports cars. These included the flat racing car front end of the pre-war cars, with Mercedes star mounted on the radiator grille. The coachbuilders in Untertürkheim and Sindelfingen spared no effort with the aluminium body. Thanks to the canted position of the engine and the aerodynamic profile they strove to create, the car was very low, free of trim right down to the underbody, with a flat front end, intuitively rounded aerodynamic lines, recessed headlamps, and wheels entirely enclosed in the bodywork. The coupé “greenhouse” was as narrow as possible, with a steeply raked windscreen that curved into the A-pillars. The elongated rear window flowed into the aerodynamic rear end. The result was a relatively small frontal area measuring 1.78 square metres. The drag coefficient was measured on a 1:5-scale model and found to be cd = 0.25 – and that without taking into account the realistic airflow through the engine compartment. But in retrospect this result proved to be rather over-optimistic. A wind tunnel measurement made on historic vehicles in January 2012 by Mercedes-Benz Classic showed a drag coefficient of cd = 0.38 for the W 194.
The car’s doors deserve a chapter all of their own: in order for the spaceframe to achieve the desired high rigidity, it had to be as wide as possible in the passenger cell area. This requirement led to the spectacular and later celebrated gullwing doors. In the earliest models, the door opening started at the waistline. Deeply recessed into the roof, the doors opened upwards, creating an image reminiscent of outspread wings. For this reason the car was dubbed “gullwing” by the North Americans and “papillon” (butterfly) by the French. Driver and passenger boarded the car from above.
In the sum of its design characteristics, the Mercedes-Benz 300 SL (W 194) was one of the most sophisticated technical products of its day. And with it was created a racing sports car that would dominate the 1952 racing season.
Development of the production sports car 300 SL (W 198)
The Mercedes-Benz 300 SL (W 194) racing coupé gave rise to the production sports car, which also boasted the model designation 300 SL but took the series number W 198. The early history of the car was turbulent, for with the promise made on 5 September 1953 to Maximilian Hoffman that a small sports car and a large sports car would be made available to him for the International Motor Sports Show in New York beginning on 6 February 1954, the Board of Management of Daimler-Benz AG had made a bold decision – bold because neither of the two vehicles yet existed. Another problem for the planners was that in Hoffman they had an importer who was an extremely active driver, a man who liked to sit behind the wheel and take part in the regular races held somewhere in the USA almost every weekend. For example, Hoffman had made Porsche known in the US and helped them gained undreamt-of success. So it was not easy for the Board members of Daimler-Benz to give the demanding “car guy” Hoffman the right thing. Above all, Hoffman wanted open-top cars. For time reasons it was not possible to deliver on the request for a large sports car. Instead, the company gambled on the exclusive GT car, which is what the production version of the 300 SL ultimately is. The men around chief engineer Fritz Nallinger and his Board of Management colleague Arnold Wychodi, responsible for exports, saw an opportunity here.
Two facts additionally confirmed them in this attitude. First, development of the petrol direct injection engine originally intended for the 300 SL (W 194) and the 1953 racing season had reached an advanced stage. And secondly, the car, its chassis and the spaceframe had performed outstandingly in many competitions in 1952. So it was an excellent basis for the production vehicle.
But all together there was still a great deal of development work to be done. For example, the developers needed a body that was more practical for everyday use, with improved ride comfort and active safety. For weight reasons, the racing sports car had no heating system and completely lacked sound insulation. So while operational noise from the transmission and rear axle was perhaps tolerated by racing drivers wearing earplugs, it was unacceptable to a gentleman driver who had just spent a handsome sum on a top-of-the-range sports car. And a production sports car had to offer a reasonable amount of luggage space. From the modern perspective, it is a minor miracle that the developers managed to bridge the considerable gap between the requirements of Daimler-Benz and the demands of Maximilian Hoffman.
Senior engineer Karl-Heinz Göschel was responsible at the time for making direct petrol injection, then still in its infancy, practical for use in a workaday vehicle. Asked later how he achieved such an impossible undertaking, he replied dryly: “We slaved day and night and had no time for meetings.”
The thunderous applause that greeted the appearance of the new 300 SL (W 198) in New York in February 1954 was loud, clear and unanimous. From engineering aficionados who delighted in the direct petrol injection, realised for the first time in the four-stroke engine of a commercial available automobile, to admirers of sheer elegance, captivated by the seductive lines of the gullwing car – no one had expected a vehicle like that from Daimler-Benz. A racing car or a racing sports car, perhaps. But a large Gran Turismo that could compete with any Italian or British car in that category, that was a sensation in the mid-1950s.
But for once the shrewd marketing professional Maximilian Hofmann was not entirely right on one point: from the outset he wanted the 300 SL as an open-top car; then, three years after the Coupé’s debut came the Roadster. However, the more glamorous automobile that sets standards even today was and remains the Mercedes-Benz 300 SL as a coupé with gullwing doors.
Development of the 190 SL (W 121 B II)
At the International Motor Sports Show in New York, alongside the Mercedes-Benz 300 SL (W 198) the brand presented the 190 SL (W 121). It was always rather overshadowed by the Gullwing, and yet its programmatic and consequently far-reaching significance and influence on the successful development of the SL model series remain tangible to this day.
The genesis of the 190 SL coincided chronologically with that of the 300 SL (W 198). As the US importer, Maximilian Hoffman was looking for sporty new cars for the North American market. What Daimler-Benz was able to offer from the product range of that period was in his eyes too conservative. He was consulted and even specially invited to Stuttgart. At that memorable meeting in Untertürkheim on 2 September 1953, the Board of Management of Daimler-Benz AG showed him the planned convertible versions of the 180 model. But Hoffman found them wanting. His bluff reaction climaxed in the now legendary statement: “This isn’t going to work.” Hoffman described the market situation as he saw it and complained, for example, about the vehicles’ drab colours and the lack of open-top sports cars in the Mercedes-Benz range. It was a point that had already been made by the Board’s export chief, Arnold Wychodil, in May 1953. Now, however, with the personal intervention of Hoffman the matter took on special urgency. Hoffman had opened an impressive showroom for Mercedes-Benz cars, but he lacked vehicles that would really attract customers into the dealership. He emphasised that although Mercedes-Benz had an excellent reputation in the USA, people there expected a sports car that could provide a basis for the existence of the dealer organisation on its own.
Daimler-Benz was in a fix. On the one hand, they did not want to offend the newly recruited, dynamic US importer Hoffman. On the other, the company did not have the product desired by Hoffman, a smart and elegant sports car. To make the situation worse, the company had given its word that Hoffman would get the product he wished for in time for the International Motor Sports Show in New York in February 1954. The drama that unfolded in autumn 1953 is apparent from the extremely tight schedule, which made direct action the norm.
Board chairman Fritz Könecke stated in his concluding remarks on 2 September 1953: “We intend to give Mr Hoffman every possible support to further pursue business in the USA, which has made a promising start.”
Könecke stated at a Board of Management meeting on 14 September 1953: “A 180 model sports car will be brought out on schedule; the two demonstration 300 SL models will be handed over to Mr Hoffman in February or March 1954.” It is not surprising that the Board began with a 180, since that was the starting point in its thinking at the time.
On 16 September 1953, the Sindelfingen plant received the first preliminary blueprints of the W 121 chassis in the American version from Design 1, the Advance Development unit under Josef Müller.
On 21 September 1953, chief engineer Dr Fritz Nallinger submitted necessary changes to the Sindelfingen design engineers Hermann Ahrens, Walter Häcker, and Karl Wilfert.
On 31 October 1953, Max Hoffman received a large airmail parcel from the Board of Management containing view drawings of the 300 SL and “the 180 model in the sports version, the name for which we are still leaving open”.
On 16 January 1954, the Board of Management visited the Sindelfingen plant to inspect the two vehicles, the 300 SL and 190 SL, destined for New York.
On 18 January 1954, a key Board of Management meeting was held: it determined all further development of the SL and set the tone for SL development to this day. Könecke repeated the decisions taken two days earlier to present both the 300 SL and the 190 SL at the show in New York in February 1954, stating that “the latter has not yet achieved its final form”. However, Nallinger’s proposal to replace the current Convertible A with the coming 190 SL had much more far-reaching implications. It was approved by the Board and remains valid today. The minutes read: “Dr Nallinger also proposes that the SL vehicles, and now the 190 SL in particular, should in future replace the A-version convertible, roadster and coupé models, with the Saloon and 4-seater Convertible-Roadster being based on the corresponding basic model, but that the version A-Convertible, Roadster and Coupé should no longer be realised with conventional lines and radiator grille but rather in the SL version.”
The debut of the 190 SL on 6 February 1954 in New York elicited no less delighted astonishment than that of the 300 SL. Both models were completely atypical of the Mercedes-Benz brand in that period, but were afforded an enthusiastic welcome.
In the advanced development phase between the New York show in February 1954 and production start-up a year later, the 190 SL underwent a mutation that in styling terms made it appear like the 300 SL’s younger brother. Remodelled by a team headed by Walter Häcker, the final version met with unanimous approval by the public. Regardless of the stylistic affinity to the 300 SL, the 190 SL was seen as a handsome car. Owing to its reliability it also became a coveted car. It played a key role in opening up the US market for Daimler-Benz in the 1950s, as demonstrated by the export figures:
Total exports of Mercedes-Benz cars to USA
1952 1953 1954  1955     1956   1957
253    423    639    2,054   3,109   6,048
of which Type 190 SL
1952 1953 1954 1955  1956   1957
-           -        -         830    1,849  1,806
In issue no. 49 in November 1956, “Automobil Revue”, Berne, published a report on the 190 SL that summed up the changes the car had undergone during its development: “The original idea of a lightweight sports car weighing only 1000 kilograms was modified in the course of time. The elegant lines that immediately won the public’s favour when the car appeared were not affected by the changes, which have turned it from a sports car into a more flexible two-seater utility and touring vehicle with a sporty character. Up to about 4000 rpm the four-cylinder engine operates smoothly and quietly; above that a strong, penetrating growl develops, accompanied by vibrations that make the rear-view mirror tremble. Despite its performance, the 190 SL is not a sports car in the true sense, but an uncomplicated, respectable touring car with all four wheels firmly on the ground, so to speak. Owing to its exemplary handling it is one of those very few vehicles with which one attains highest average speeds in full safety without undue haste.”
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