- The ultimate in streamlining: a drag coefficient of Cd = 0.36 documents realisation of the perfect solution
- The most exacting design for a streamlined vehicle on the basis of the sporty top model, the 540 K
- The perfect candidate as a test vehicle for high-speed tyres at Dunlop
The 1920s and 1930s were characterised, in automotive terms, by the steadily increasing speed of travel. The development of fast roads ways and long-distance routes reflected this change, while the era also saw the advent of the motorway. The automotive industry took advantage of this progress. Not just with more powerful engines and redesigned suspensions: vehicle bodies, for example, grew more sophisticated in design, while streamlined vehicles also emerged.
Against this backdrop, Mercedes-Benz went on to build several vehicles with aerodynamically shaped bodies. The 540 K Streamliner, produced in 1938, marked the culmination in this respect for the time being. The 540 K was Mercedes-Benz’s sporty top model in the 1930s. Customised body shell creations, individually manufactured, had always represented the exclusive norm for Mercedes-Benz, and the “special vehicle production” unit at the Sindelfingen plant made the realisation of such singular ideas possible.
The styling experts at Mercedes-Benz – the term ‘designer’ as we know it today did not yet exist – created a whole series of aerodynamically shaped body shells for the 540 K during 1937 and 1938, all of which reflected the concept of aerodynamic flow to a greater or lesser extent. The Streamliner produced in 1938 was not only a masterpiece of design, but also demonstrated the most thorough application of the knowledge gained in the tests in the wind tunnel.
Achieving even higher cruising speeds than the 140 to 145 km/h (87 to 90 mph) usually associated with a 540 K demanded numerous detailed measures. Some of the most important of these involved the car’s aerodynamics: a 540 K in the standard version, with a coupé body, achieved a Cd figure of around 0.57 – too much for higher cruising speeds. For this, a more streamlined body with an considerably improved Cd figure was required. The 540 K Streamliner met the criterion, as wind tunnel measurements undertaken by Mercedes-Benz Classic in May 2014 go to prove: it achieves the exquisite figure of Cd = 0.36. The results are cruising speeds of 165 to 170 km/h (103 to 106 mph) and with supercharger a top speed of 185 km/h (115 mph).
These were the requirements that led to the creation of the body shell of the 540 K Streamliner of 1938. It was systematically designed to meet the aerodynamic specifications: shaped from front to rear to allow the air to flow perfectly over it and to offer as little resistance as possible to the wind. The windscreens are curved to the sides. The roof line is set low, tapering to a point in the middle of the back and merging from there into the horizontal line of the softly curved rear section. The headlamps are fully integrated. At each point where the air flow risks breaking away, the designers have optimised the details, for example by recessing the door handles, omitting the bumpers or reducing the panel gaps. The underbody is completely panelled, so minimising obstructions to the air flow here too.
The requirement to achieve high cruising speeds also dictated an adjustment to the drive axle ratio, which was lengthened from i = 3.08 to i = 2.90. In all other technical details the car matched the standard version of the 540 K.
Just how seriously the builders of the vehicle took their responsibility is demonstrated by the Mercedes star: it does not stand proud, but is painted on – as in the case of the Silver Arrows, the renowned Grand Prix racing cars. Also like these, the streamlined 540 K was given silver paintwork.
From today’s perspective it could be seen as something of a historical irony that the classic, vertical Mercedes-Benz pointed radiator grille was nevertheless still to be found below the body shell and remained a decisive factor in the appearance of the front section. Of course practical aspects of thermal management also played a role here, but a styling element that is as characteristic of the brand as the classic Mercedes radiator is subject to special protection – hardly surprising then, that the subject was a talking point at the time right up to Management Board level. This whole process demonstrates the extent to which the automotive industry at the time was changing and how it balanced on the very threshold between the traditional and the modern.
The resulting overall appearance of the 540 K Streamliner was of a powerful sports car, the potential of which to achieve high cruising speeds was immediately clear to the casual observer: doubtless this exceptional one-off vehicle caused a considerable stir when it first appeared.
Much of the praise around this vehicle is also due to Max Sailer. From 1935 on he was a deputy board member of Daimler-Benz and responsible for overall vehicle development for the Mercedes-Benz brand, including for its successful racing and record-breaking vehicles. He was thus very well aware of the significance of aerodynamics in motor vehicle construction and was one of the driving forces behind corresponding projects, also in relation to series-production vehicles.
The extraordinary 540 K was built by the special vehicle production unit in the first half of 1938. In June it was delivered by the Daimler-Benz dealership in Frankfurt am Main to the Deutsche Dunlop Gummi Comp. AG (German Dunlop Rubber Company) in Hanau. The company put this high-performance vehicle to specific use for tyre testing, as the ever-higher speeds at which cars were now travelling demanded new designs and materials for tyres that would enable them to withstand the more powerful forces to which they were exposed. These had then to be subjected to real-life testing, which was all the more necessary for powerful, heavy and fast cars.
And so the 540 K Streamliner really came into its own. Far more so than any other vehicle of that era, its aerodynamically styled body and powerful engine made it eminently capable of rapid supercharged acceleration to speeds as high as 185 km/h (115 mph) on the – in those days still very empty – German autobahns. It smoothly sustains cruising speeds of 165 to 170 km/h (103 to 106 mph) over a considerable period. We can only guess at the extreme concentration and tension on the part of the test drivers. Because, at the speeds at which they were driving, a tyre malfunction was something to be reckoned with at any moment, they were all the more dependent on a reliable and predictable vehicle that would ensure the driver-fitness safety of its occupants over longer periods of driving at the critical limits. The 540 K Streamliner was ideally suited for this task.
According to the commission book Dunlop ordered a 540 K, one of the fastest passenger cars in existence at the time, from the Daimler-Benz dealership in Frankfurt on Main on 23 December 1937. A line drawing, dated 8 February 1938, was produced in the special vehicle production unit headed by Hermann Ahrens. This provided the precise manufacturing specification for a body shell previously tested on the model in the wind tunnel. At around the same time, incidentally, another design with almost identical lines was taking shape on the drawing board, in this case though as a Cabriolet B.
The vehicle ordered by Dunlop appears in the company’s documents dated 10 March 1938 with the comment “Schl. Si.”: Four weeks after the drawing had been made the chassis was trucked from Untertürkheim to the special vehicle production unit at the Sindelfingen plant, where it was fitted with the body that had been assembled there for it. In those days, the final assembly of most Mercedes-Benz passenger cars took place at the Untertürkheim plant, and the body shells were normally transported there from Sindelfingen. In the case of the 540 K it was done the other way round.
Further sources provide the following information: the vehicle registration document was issued by Daimler-Benz on 20 May 1938. Three weeks later, on 14 June 1938, the vehicle was registered in Hanau, where Dunlop was based, and given the registration number IT-146901. Ten days later, on 24 June 1938, an entry appeared in the books of the “Sammelstelle für Nachrichten über Kraftfahrzeuge,” or Central Office of Motor Vehicle Informationin Berlin. All this happened even before the streamlined 540 K was handed over to the Daimler-Benz dealership in Frankfurt; and this the commission book records as having taken place on 25 June 1938.