Mercedes-Benz Grand-Prix racing car W 25, 1936

Mercedes-Benz Grand-Prix racing car W 25, 1936

After the 1935 motor racing season that had been so successful for Mercedes-Benz, culminating in Rudolf Caracciola winning the European Grand Prix Championship for the first time, the W 25 750 kg Formula racing car that had proved its qualities over the last two years was radically revised for 1936.

Although its dominance in the past season had been overwhelming, its last remaining competitor, Auto Union, with its avant-garde Type B racing car powered by a supercharged V16 mid-mounted engine, had not been resting. For 1936, the Zwickau engineers increased the displacement of the spectacular power unit to just over 6 litres, which, depending on the fuel mixture used, resulted in a power increase to between 485 hp/357 kW and 520 hp/382 kW at 5000 rpm - a real challenge for the development team led by Daimler-Benz chief engineer Dr Hans Nibel.

The suspension of the W 25, with its double-joint swing axle suffering from a lack of track and camber stability, had also reached its limits with the peak output of the M 25 C inline eight-cylinder engine, which ranged between 398 hp/293 kW and 462 hp/340 kW. In short: in order to be able to compete at least on an equal footing with the increasingly strong competition, the W 25 had to undergo considerable further development in almost all technical areas.

Especially with regard to the power unit, this task turned out to be quite difficult. Although the new increase in displacement to 4740 cc through a massive enlargement of the bore by 4 mm to 86 mm was just as effective a means of increasing performance as the use of enlarged valves with a disc diameter of 37 mm, it became apparent that the basic concept of the eight-cylinder inline engine, whose last evolutionary stage had been given the designation ME 25, no longer permitted any major leaps in development. All parameters of the physical load were approaching the limit. The compressor technology in particular was a source of concern for the developers: the high temperature level reached in the ME 25, bolstered by a rotary vane height that had now increased to 255 mm, resulted in significantly increased susceptibility to damage on the part of the Roots blower. Some of the engines were therefore also equipped with compressors whose rotary vanes still had a height of 240 mm.

The peak output of the revised engine was measured at 494 hp/363 kW at 5800 rpm. The displacement deficit of the Mercedes-Benz racing engine of a good 1200 cc compared to the V16 in the Auto Union Type B now began to show its impact - not just in absolute figures, but also in the character of the power delivery.

In addition to the engine, the development team paid full attention to the car as a whole. If there was a risk of falling behind in terms of performance, the frame, suspension and body of the W 25 for 1936 had to meet the very highest requirements in order to ensure competitiveness. For this reason, the decision was made in Untertürkheim to make the new W 25 shorter, more compact and lighter, and to equip it with a new body and a newly developed rear axle.

In order to achieve the former, the previous wheelbase was shortened from 2715 mm to 2505 mm - which incidentally led to the new internal designation of the car "W 25 short". Adapted to the shortened chassis, the redesigned aluminium body featured a circular rather than oval cross-section as previously, giving it a lower and more streamlined appearance. However, the tall Manfred von Brauchitsch suffered from a lack of space in the much smaller cockpit. As before, the protruding wheel suspension elements on the front and rear axles were encased in cladding as far as possible. A characteristic feature of the W 25 of the 1936 season was the pointed rear end, which extended far beyond the rear end of the frame and promised additional aerodynamic advantages.

The low design of the car was helped by the modified positioning of the 4-speed gearbox. Instead of longitudinally, as before, it was now arranged transversely under the differential, which made an even lower position for the propeller shaft possible. Power was now transmitted from the gearbox to the differential via a pair of spur gears.

Since the chassis had already become increasingly apparent as a weak point in the 1935 season with the power level of the engine that had been reached in the meantime, a completely new rear axle design was presented in the car for 1936. Instead of the overburdened double-joint swing axle, which on the one hand transmitted too little drive power, especially when cornering, and on the other hand constantly demanded the utmost attention from the drivers, a de Dion axle was now used, whose special qualities lay in inherent track and camber stability as well as a reduction in unsprung masses.

Since the front axle design with its unusual solution of coil springs located in the axle tube remained untouched, the intended improvement in handling was only partially achieved: Although the revised W 25 was much more docile and easier to control at high cornering speeds than its predecessor with a longer wheelbase, the insufficient front suspension travel still led to jolts in the steering wheel and a strong axle tramp tendency of the front axle in poor road conditions.

The intended weight reduction could also not be realised despite the considerable wheelbase reduction. Like its predecessors from 1934 and 1935, the W 25 weighed in at 847 kg. The apparent contradiction with the 750 kg Formula is explained by the fact that the weight limit referred to cars without tyres, oil and coolant.

A total of six examples of the short W 25 were built. The first had already been completed in late summer 1935 and had managed to compete in the Swiss and Italian Grands Prix. In contrast to the previous year, the 1936 European Grand Prix Championship comprised only four races, and the newly developed cars competed in only three of them. The season opener in mid-April got off to a promising start when Rudolf Caracciola was able to show off the strengths of the W 25 short, which was now much more compact and had better road-holding, to its best advantage on the twisty track in Monte Carlo and saw the chequered flag as the winner of the rainy Monaco Grand Prix. On this occasion, the driver from Remagen clearly distanced himself from the more powerful Auto Union Type Bs, which could only be controlled with great difficulty in the narrow streets of the principality and especially on wet roads, and relegated Achille Varzi and Hans Stuck to second and third places.

The picture changed in the German Grand Prix held on the Nürburgring at the end of July. In the Eifel, the V16 mid-engined race cars from Zwickau were able to exploit their clear power and torque advantages and took a double victory with the new young star Bernd Rosemeyer and the Italian Achille Varzi, who had switched from the Mercedes-Benz racing team the year before. The fact that only two of the five W 25s short entered actually finished and that Luigi Fagioli was the best-placed Mercedes-Benz driver one lap down in fifth place did not bode well for the two remaining races of the European Grand Prix Championship, which took place on the fast to very fast circuits in Bremgarten/Bern and Monza.

In fact, in the Swiss Grand Prix at the end of August it became apparent that the latest version of the W 25 had no chance against the displacement giants from Zwickau, despite all the technical developments implemented for the 1936 season. The race ended with a triple victory for Auto Union by Rosemeyer, Varzi and Stuck. The racing team from Untertürkheim, which had entered with four cars, had to be content with the fourth place of Hermann Lang and Rudolf Caracciola, who had taken over Lang's car after his own retirement. The W 25s short of Fagioli and von Brauchitsch had also failed to finish after defects.

Due to the disappointing results for the season and the recognisable inferiority of its own material, Daimler-Benz withdrew from the rest of the season after the race in Bern. The following year, however, they celebrated a triumphant return to the Grand Prix scene with a new 750 kg Formula racing car called the W 125.

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