The Mercedes-Benz Museum in Stuttgart has produced a series of “close ups” on many of the special machines in its priceless collection. Likely the fastest of all was the 1937 W 25 streamliner, with a measured top speed of 380kph (236mph) on the smooth and spacious Avus oval.
Here are some of the details, courtesy M-B:
Streamlined: Flowing curves and curved surfaces of silver-colored sheet metal envelop the W 25 streamliner. Almost organically, the front and rear wheel arches curve upwards from the aerodynamically optimized body, the wheels clad with covers that could be folded up for maintenance work. For this specialized vehicle, the Mercedes-Benz engineers explored the outer limits of streamlining and driveline technology available at that time.
Trio: M-B entered three streamlined racing cars in the formula-free International Avus Race in Berlin on May 30, 1937—all similar in appearance but with notable technical differences. In addition to the W 25 streamlined racing car with 5.6-liter 12-cylinder MD 25 DAB engine on display in the Museum, two vehicles with the 5.7-liter 8-cylinder M 125 F engine from the then-current W 125 single-seater were also developed for the race.
Three times on the podium: The novel vehicles were successful across the board: Rudolf Caracciola won the preliminary race and Manfred von Brauchitsch took top honors in the second preliminary with the vehicle exhibited in the Mercedes-Benz Museum. The overall winner of the main race was Hermann Lang. Englishman Richard Seaman had no chance against all three, competing in a classic Mercedes-Benz W 125 with free-standing wheels.
Technology: The Avus Race was a victory for aerodynamics as on the long straights, the vehicles touched more than 230mph. For comparison, the final version of the W 25 formula racing car with free-standing wheels and 4.7-liter 8-cylinder engine from 1936 reached “just” 186mph.
Exclusive: Conventional racing cars in the 1930s were made by hand and in very small numbers. The streamlined racing cars were even more exclusive. Von Brauchitsch’s vehicle was based on a W 25 record car with a 12-cylinder engine that the factory successfully used in 1936—an optimal starting point for the “fastest race in the world” (in the words of Herrmann Lang) on the Avus. The body of the ’36 record-breaker was significantly modified for the ’37 Avus Race.
Flap: Only the heads of the racers in the M-B streamliners could be seen at Avus. After the drivers took their respective seats in the vehicle, a carefully shaped sheet metal cover hinged at the front was folded down over the cockpit. Shoulders and arms disappeared. Protection against the wind was provided by a wind deflector consisting of three small panes mounted on the flap.
Drivers Eye View: The wind deflector allowed limited visibility of the track during the speedy ride. This was an impressive experience, especially on the steeply banked curves. Lang would write about this later: “Driving through this Avus-Nordschleife – a unique curve – properly was a problem and required a lot of training. At first, I just couldn’t take my eyes off the line indicating the centre line of this track. Later, I ventured a glance to the side now and then. If I looked to the right, I had the strange impression of driving up a vertical wall; if I looked to the left, I seemed to see, deep below me, a sea of faces filling the interior of the curve.”
Science: The optimized aerodynamics of the streamlined body accounted for much of the cars’ outrageous top speed. Mercedes-Benz engineers drew on findings from the record-breaking runs of 1936 and from work in the Friedrichshafen wind tunnel. In 1936, the “Allgemeine Automobil-Zeitung” (an automotive newspaper) wrote about the important effect of supposedly insignificant details such as the clad wheels: “That was no wasted effort because the drag of the unclad wheels swallowed up three quarters of the total power…”
First success: Aerodynamic innovation played a major role at the 1937 race, and was importantly especially for Manfred von Brauchitsch. For it was on this track, five years earlier in 1932, that the brilliant German had won in a private Mercedes-Benz SSKL featuring an innovative streamlined body designed by aerodynamics pioneer Reinhard von Koenig-Fachsenfeld. Von Brauchitsch’s success put the importance of an aerodynamically designed body on the engineers’ agenda – first for racing cars and exclusive vehicles with “motorway courier” bodies, and later for production vehicles as well.