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
Monaco Grand Prix, August 8, 1937: Winner Manfred von Brauchitsch and runner-up Rudolf Caracciola in the Loews corner, both of them driving Mercedes-Benz W 125 formula racing cars.
Masaryk Grand Prix near Brünn, 26 September 1937. Richard Seaman (number 6) on Mercedes-Benz W 125 finished fourth.
Mercedes-Benz formula racing car W 125, 1937.
Tripoli Grand Prix, Mallaha, May 9, 1937. The winner Hermann Lang at the wheel of a Mercedes-Benz W 125.
Mercedes-Benz formula racing car W 125, 1937.
Swiss Grand Prix, Bremgarten, August 22, 1937. Rudolf Caracciola, who was to win the race, with start number 14 in a Mercedes-Benz W 125.  In the fore: Bernd Rosenmeyer (start number 8) and Hans Stuck (start number 10), both in Auto Union.
Coppa Acerbo, Pescara, August 1937. Manfred von Brauchitsch (start number 14) finished in second place at the wheel of a Mercedes-Benz W 125.
Manfred von Brauchitsch ahead of Richard Seaman at the Masaryk Grand Prix in Brno. They finished in 2nd and 4th respectively, with Rudolf Caracciola winning the race. All driving the Mercedes-Benz W 125 750 kilogram racing car..
Double victory at the Italian Grand Prix in Livorno, September 12, 1937. The winner Rudolf Caracciola (start number 2) and Herman Lang (start number 6), who finished in second place, both in Mercedes-Benz formula racing cars W 125.
Mercedes-Benz formula racing car W 125, 1937 (on the test track in Untertürkheim, 1972).
Cutaway drawing of the Mercedes-Benz W 125 racing car, 1937.
The superior car of the 1937 season: The Mercedes-Benz W 125 formula racing car.
German Grand Prix at Nürburgring, 25 July 1937. Soon after the start in the south bend, the field is led by Hermann Lang with starting number 16 and the subsequent winner, Rudolf Caracciola, with starting number 12, in the Mercedes-Benz formula racing car W 125. Behind them are Bernd Rosemeyer and Hans Peter Müller, both in Auto Union, followed by Manfred von Brauchitsch (second place), also in a Mercedes-Benz W 125.
Mercedes-Benz sports cars – here a W 125 Grand Prix racing car – were part of a special exhibition at the 1938 International Motor Show.
Mercedes-Benz W 125
Mercedes-Benz W 125