Mercedes-Benz W 125 record car, 1938
From 1934 until 1939, Mercedes-Benz and Auto Union were competing not only on the grand prix tracks, but also with record attempts. Special cars, which didn’t have to comply with the grand prix formula, were designed with the highest power and speed in mind. The drivers were Rudolf Caracciola for Mercedes-Benz and Bernd Rosemeyer for Auto Union. After Rosemeyer had been ahead by a nose in the German record week in October 1937 with his fully faired Auto Union car, the Mercedes-Benz record car was fundamentally revised.
In January 1938 the Mercedes-Benz racing team competed with a fully faired car with a completely newly developed body. Characteristic features were the drawn down wheel covers and the very long rear section with a distinct separation line. The final body shape had been optimised in the wind canal of the Deutsche Versuchsanstalt für Luftfahrt (DVL) in Berlin-Adlershof with arduous fine-tuning through 52 singular measurements on the original car. Chassis and engine matched the version that was already used in October 1937.
The chassis came from the W 125, the successful grand prix racing car of the 1937 season. The engine was the 5.6-litre twelve-cylinder M 25 DAB with an improved power output of 736 hp through conversion to a suction carburettor and fitting of an additional carburettor. By relinquishing the conventional cooler, the air intake vent at the front could be made smaller, which reduced the drag coefficient to 0.157. Engine cooling was converted to ice cooling: In a box in the car front were 100 kg of ice and a small amount of water – enough for a record attempt.
On 28 January 1938, Rudolf Caracciola drove at a speed of 432.7 km/h over a distance of one kilometre or 432.4 km/h over a distance of one mile on the Frankfurt-Darmstadt autobahn, each time with a flying start and as an average of the drive to and from. Therewith, he achieved the highest speed ever driven on public roads. During the attempt to beat Caracciola’s record on the same day, Rosemeyer’s Auto Union record car was caught by a gust of wind and veered from the road, fatally crashing. Rosemeyer met his death.