Mercedes-Benz Grand-Prix racing car W 25, 1935

The development team led by Daimler-Benz chief engineer Dr Hans Nibel used the break in racing during the winter of 1934/35 to further improve the 750 kg Formula W 25 racing car that had been used for the first time the year before. During the numerous races of the past season, it had become apparent time and again that the reliability of the cars did not yet consistently meet the required standards. Above all, the engine itself, which was clearly superior to the competition in terms of performance, as well as its peripherals, had caused more failures than were acceptable. It was not until the revised M 25 B engine was introduced in August 1934 that there was a noticeable improvement in the situation.

For the 1935 season, this evolutionary stage of the supercharged inline eight-cylinder engine was initially retained. With a stroke lengthened to 94.5 mm and the unchanged bore of 82 mm, the displacement of the power unit had grown to a total of 3992 cc. In combination with a higher-throughput Roots blower with 240 mm rotary vanes, the peak outputs reached unprecedented levels depending on the fuel used: they ranged between 370 hp/272 kW and 430 hp/316 kW at a rated speed of 5800 rpm in each case. Above all, the torque maximum had increased and was now 500 Nm.

The cars of the previous competitors Alfa Romeo and Bugatti could not keep up in terms of engine output, nor could the Maserati marque, which in the meantime had become more prominent, with its powerful six- and eight-cylinder cars. The driving force behind this veritable explosion in performance was the intense competition with the rival from Zwickau: the V16 of the Auto Union mid-engined Type B racing car had been increased in capacity to 5 litres for the 1935 season, resulting in an increase in maximum output to 375 hp/276 kW.

With the third evolutionary stage of the inline eight-cylinder engine, called the M 25 C, which was raced for the first time in July 1935, the Mercedes-Benz racing department restored the former lead over Auto Union. Instead of 94.5 mm, the stroke was now 102 mm, which resulted in a displacement that had increased to a total of 4309 cc. Although the company refrained from increasing the delivery capacity of the supercharger again following bench tests, a peak output of between 398 hp/293 kW and 462 hp/340 kW was documented for the M 25 C, depending on the fuel mixture - without a doubt, the most powerful engines for Grand Prix racing cars according to the 750 kg Formula in the 1935 season again came from Untertürkheim.

Since the Mercedes-Benz racing department had in the meantime built two more W 25s, an extensive programme of racing events had been developed for the otherwise technically largely unchanged vehicles. The focus of the first full season was, of course, on those seven races whose results counted towards the Grand Prix European Championship awarded for the first time by the supreme motorsport authority, the Association Internationale des Automobile Clubs Reconnus (AIACR).

Already in the first of these events, the Monaco Grand Prix held at the end of April, Luigi Fagioli's victory indicated that the W 25 would become the dominant car of the first European Championship season. While the light-footed Alfa Romeo P3s still played a leading role on the narrow circuit in the principality in second and third place, the true balance of power was revealed at the Grand Prix de l'ACF in Montlhéry at the end of June: Rudolf Caracciola and Manfred von Brauchitsch scored a one-two for Mercedes-Benz on the high-speed circuit, a success that was rounded off by Fagioli taking fourth place. Achille Varzi finished fifth, five laps behind, in the Auto Union Type B.

The situation was similar in mid-July in the Belgian Grand Prix in Spa-Francorchamps: double victory for the W 25s of Caracciola and Fagioli ahead of two Alfa Romeos. Two weeks later, however, an episode occurred that was to go down in the motorsport history books. Despite a large contingent of five Mercedes-Benz W 25s and four Auto Union Type Bs, Italian driving legend Tazio Nuvolari in an Alfa Romeo P3 managed to take victory in the German Grand Prix on the Nürburgring thanks to a brilliant driving performance. As the best Mercedes-Benz driver on home soil, Rudolf Caracciola only placed third - despite the performance-enhanced M 25 C engine used for the first time in his W 25.

The Remagen native set the record straight at the end of August in the Swiss Grand Prix on the Berner Bremgarten Circuit and won ahead of his Italian team-mate Luigi Fagioli. He relegated the two Auto Union drivers Rosemeyer and Varzi to third and fourth place. In addition, sixth place went to Mercedes-Benz junior driver Hermann Lang.

After the W 25s had won four of the first five races counting towards the European Grand Prix Championship, the first bitter defeat came in the Italian Grand Prix in Monza. None of the four cars that started saw the chequered flag - instead, Hans Stuck in an Auto Union triumphed ahead of René Dreyfus in an Alfa Romeo and Paul Pietsch in another Auto Union.

The last race of the European Grand Prix Championship, the Spanish Grand Prix, took place at the end of September on the Circuito Lasarte road circuit near San Sebastian. Caracciola, Fagioli and von Brauchitsch documented the dominance of the W 25 once again with their triple victory at the end of the season. In addition, Rudolf Caracciola secured the European Championship title in the overall standings ahead of his team-mate Luigi Fagioli.

Both drivers similarly left their mark on other non-European Championship races in which Mercedes-Benz also competed during the 1935 season. While Caracciola won the Tripoli Grand Prix in mid-May and the Eifel Race on the Nürburgring in mid-June, Fagioli won the AVUS race at the end of May and the Gran Premio de Penya Rhin on the Montjuic Circuit in Barcelona at the end of June.

Without a doubt: the motor racing year 1935 was clearly dominated by the Mercedes-Benz W 25, whose initial problems from the previous year had been successfully rectified.