Mercedes 120 hp "Gordon Bennett" racing car, 1905
For the 1905 motor racing season, the Mercedes 90 hp racing car, which had been somewhat unsuccessful in 1903 and 1904, was revised. The focus of the further development work was of course on increasing the engine output, while virtually no changes were made to the basic concept or to other aspects of the vehicle's technical design.
The displacement of the four-cylinder engine designed by Josef Brauner, with its characteristic IOE valve arrangement, was increased compared to the previous year's model by enlarging the bore and stroke to 175 x 146 mm, resulting in a displacement of 14,047 cc. Despite the enormous cylinder dimensions the aim here, as with the 90 hp model of 1903 and 1904, was still to keep the overall height of the engine as low as possible for aerodynamic reasons, as a result of which the team again opted for an oversquare, i.e. short-stroke, design of the power unit. Thanks to the increase in displacement and a modified carburettor configuration, the peak output of the engine was increased to around 110 to 120 hp/81 to 88 kW at approx. 1200 rpm - unfortunately, the sources do not allow more precise details. However, contemporary press reports refer to the car as a Mercedes 120 hp.
Following the introduction of a foot-operated accelerator pedal in the 90 hp racing car the previous year, the gearshift lever, which had previously been mounted on the outside, was now relocated to the interior of the car to make operation even easier. Externally, the higher body in the entrance area and, above all, the barrel-shaped fuel tank located behind the seats at the rear of the frame, which replaced the previously used square petrol tank between the rear wheels, caught the eye. The frame, the chassis and the water-cooled brake system were carried over unchanged from the 90 hp predecessor model.
Despite all the technical developments and the unconditional commitment of Camille Jenatzy and the other DMG works drivers, the new racing car's track record remained modest. At the most important motor sport events of the 1905 season, the Gordon Bennett Cup race held in France at the beginning of July and the Vanderbilt Cup Race held in Long Island/New York in mid-October, the 120 hp car failed to achieve any meaningful results. A lack of reliability, accidents and the technological gap between Continental tyres and the leading Michelin tyres were the main reasons for the disappointing performance.
The Gordon Bennett race, which was held for the last time on 5 July 1905 after numerous disputes - in particular over the limit of three cars per nation - saw six Mercedes 120 hp cars compete: three for Germany, with Camille Jenatzy, Pierre de Caters and Wilhelm Werner at the wheel, and three for Austria with Hermann Braun, Otto Hieronimus and Alexander Burton. As in the previous year, the winner was Théry in a Richard-Brasier; the best-placed Mercedes driver was Werner in 5th place; de Caters came 7th and Braun 10th. Hieronimus and Burton were eliminated in the second of four rounds, Jenatzy in the third.
The results of the Ardennes race on 7 August and the second Vanderbilt Cup race on 14 October were even less satisfactory. Baron de Caters only achieved a 6th place on the Ardennes circuit. Jenatzy retired in the penultimate of five laps with a broken rim due to a puncture. The Vanderbilt Cup showed that things could still get worse: the Mercedes 120 hp cars driven by John B. Warden, Foxhall Keene and Camille Jenatzy retired on the 7th, 6th and 2nd of a total of 10 laps.
The Gaillon mountain race on 15 October, on the other hand, was more pleasing: Pierre de Caters took victory in the heavy car class and - together with Cissac on a Peugeot motorbike - also the overall victory with an average speed of 116.2 km/h. Four weeks earlier, at the seventh Semmering Race on 17 September 1905, Hermann Braun in Theodor Dreher's Austrian Mercedes 120 hp had improved his own record from the previous year with 7 minutes and 50.8 seconds or 76.5 km/h, thus defending the challenge trophy for Dreher.
Despite this reasonably successful end to the season, it could not be overlooked that extensive further developments were required at DMG if participation in the 1906 racing season was to prove successful.