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  Mercedes-Benz W25K

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Country of origin:Germany
Produced in:1936
Predecessor:Mercedes-Benz W25
Successor:Mercedes-Benz W125
Author:Wouter Melissen
Last updated:July 21, 2009
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Click here to download printer friendly versionLike the altogether more adventurous, V16 powered, mid-engined Auto Unions, the new Mercedes-Benz W25 debuted at the 1934 Avusrennen. During practice the cars had major carburetor problems and the W25s were withdrawn from the race, which was duly won by an Alfa Romeo after the very quick Auto Unions had retired. With the engines fully sorted, the cars appeared next at the Eiffelrennen on the Nürburgring. Popular myth has it that the legendary 'Silver Arrow' was born here. According to the memoirs of both team-leader Alfred Neubauer and lead-driver Manfred Von Brauchitsch the white paint had to be scraped off the W25s overnight to get them underweight for the race. They re-appeared in bare-aluminium on race day and Von Brauchitsch won the race. This story only appeared in the 1950s and a little digging revealed that the name 'Silber Pfeil' had first been used by radio commentators in 1932 for the silver Mercedes-Benz raced by Von Brauchitsch himself, the Auto Unions were already 'painted' silver at Avus and the Eiffelrennen event was held under 'free formula' regulations so there was no need to get the weight down in the first place. Regardless, Von Brauchitsch' victory did herald the dawn of the 'Silver Arrow' era.

Throughout the 1934 season the two German manufacturers proved to have the quickest cars but reliability issues still handed numerous victories to the competition. The W25 nevertheless won the Klaussenpass hillclimb, the Coppa Acerbo and two Italian and Spanish Grands Prix. The original M25A was continuously developed. The first evolution was the M25AB, which featured a slightly larger bore and a boost in power to 348 bhp. By the end of the year the 4-litre M25B engine was good for 370 bhp but weighed only 4 kg more than the original M25A. Now fully reliable, the W25 dominated the 1935 season, scoring 9 major victories. A painful exception was the loss at the German Grand Prix to Tazio Nuvolari in an Alfa Romeo in front of the Reichs Chancellor. Rudolf Caracciola was well-deservedly crowned European Champion at the end of the season. By that time the M25 had evolved into the C specification, which displaced 4.3 litre and produced just over 400 bhp. The Mercedes-Benz engineers also experimented with different aerodynamic tweaks and for the high-speed Avusrennen a streamlined version with a closed cockpit was tried.

Although still referred to as the W25, the 1936 Mercedes-Benz Grand Prix car incorporated enough changes to warrant a new type name. The rear-end of the chassis was completely altered; a transversely mounted gearbox was used and the swing-axles were replaced by a more sophisticated DeDion-axle. To keep the weight under the maximum 25 cm was cut out of the center of the car. A new V12 engine had been designed but it was overweight. As a stop-gap the M25C was evolved into the 4.7 litre and 453 bhp ME25, which was actually lighter than its immediate predecessor. The W25K (for Kurz or short) failed to fill the footsteps left by the original W25, particularly due to its poor handling characteristics. Caracciola managed to win only two Grands Prix in a season dominated by Bernd Rosemeyer in his 6-litre Auto Union Type C. Mercedes-Benz got things right again in 1937 with the W125 that used an all new chassis and an even larger engine. The last hurrah for the W25, ironically, came at the Avusrennen. The 1937 edition was run under free formula regulations and attracted some of the wildest Grand Prix cars ever constructed. Hermann Lang eventually took the victory in a lengthened 1936 W25 fitted with a fully enveloping body and the stillborn V12 engine that produced a staggering 736 bhp.

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