Mercedes-Benz W 125 (1937)

Aug 20, 2012
  • Dominant vehicle of the 1937 season
  • Completely redesigned racing car
  • Engine output of more than 600 hp (441 kW)
In the wake of the disappointing performance of the modified W 25 in its third season (1936), Mercedes-Benz developed a new vehicle specifically for the last year of racing under the formula that was to be discontinued in 1937. Rudolf Caracciola's record-breaking attempts during the winter of 1936 had already given an indication of the potential for innovation within the Stuttgart racing department. That November and December, on the new autobahn (motorway) between Frankfurt and Darmstadt and in the Mercedes-Benz twelve-cylinder streamlined record-breaking model, Caracciola set five international class records and one world record. In doing so he also beat by a considerable margin the figures achieved in the same spot just a few months earlier, in March that year, by Hans Stuck in an Auto Union car.
The year 1937 was dominated by the new W 125 with an eight-cylinder engine and mechanical supercharger, which produced a top performance of around 600 hp (441 kW) from a displacement of 5.6 litres. The W 125 was designed by a young engineer, just 30 years of age, who had been put in charge of the newly created racing department in the middle of 1936: Rudolf Uhlenhaut. He not only developed new design concepts, but also tested the racing cars himself – he was a talented driver and often just as fast as the drivers who were officially on the payroll. Thanks to him, Mercedes-Benz was once again able to take its place at the forefront of European motor racing. Uhlenhaut was a man who focused on delivering detailed technical solutions. For the first time on a Silver Arrow, the supercharger was fitted downstream of the carburettors – with the effect that the turbocharger was actually compressing the final mixture. This in-line eight-cylinder engine represents the most advanced stage of development reached by the Grand Prix engine that had been in service since 1934.
The backbone of the vehicle was formed by an extraordinarily robust tubular frame made out of a special steel alloy and characterised by its four cross-members and elliptical cross-section. The wheels at the front were controlled by double-wishbone steering with coil springs. At the back, a De Dion double-jointed axle with lengthwise-mounted torsion bar springs and hydraulic lever-type shock absorbers ensured constant camber. Lateral control arms were used to pass the acceleration and braking torque through to the chassis.
Upside down world for the suspension of the W 125
After extensive test drives on the Nürburgring circuit, Rudolf Uhlenhaut opted for a revolutionary chassis design. He replaced the hitherto customary principle of hard springs and minimal damping with the complete opposite. The W 125 featured a soft-sprung suspension, with extremely long shock courses for the springs, complemented by a high level of damping, so establishing the pattern for Mercedes-Benz sports cars even today. In exterior appearance it was very similar to its predecessor. What made the W 125 unmistakable, however, were the three cooling vents in its front section. The W 125 had open wheels: the car was only fitted with a streamlined body for the very fast Avus race on 30 May 1937.
Victory followed victory in the 1937 racing season: Hermann Lang won the Tripoli Grand Prix as well as the Avus race, on that occasion in the aerodynamically optimised W 125. His average speed in this race of 271.7 km/h was not surpassed until 1959. In the Eifel race, Caracciola and von Brauchitsch finished second and third respectively, while Caracciola won the German Grand Prix, also ahead of von Brauchitsch. Manfred von Brauchitsch went on to win the Monaco Grand Prix, with Caracciola and Christian Kautz as well as Goffredo Zehender (5th) close behind him. At the Swiss Grand Prix the winners’ podium was occupied by Caracciola, Lang, and von Brauchitsch, while victory in the Italian Grand Prix was claimed by Caracciola ahead of Lang. The record year was then rounded off at the Masaryk Grand Prix in Brno, won by Caracciola with von Brauchitsch in second place. Despite his best efforts, Bernd Rosemeyer was only able to win four races in the Auto Union car. The superiority of the Mercedes-Benz team was underlined by the fact that its drivers took the first four places in the European Championship: Caracciola followed by von Brauchitsch, Lang, and the Swiss driver Christian Kautz. The year 1937 marked a high point for Mercedes-Benz, but also brought the end of the 750-kilogram formula. A new regulation would come into force from 1938.
Mercedes-Benz W 125
Year of construction:
8, in-line
5,663 cc
592 hp (435 kW)
Top speed:
over 320 km/h