Winner: Lautenschlager in a 140 hp Mercedes (average speed 111.1 km/h),
2nd Héméry in a 120 hp Benz,
3rd Hanriot in a 120 hp Benz.
Inspired not least by the economic success of the previous year's race, the organisers of the A.C.F. decided to hold the Grand Prix on the circuit near the northern French town of Dieppe again in 1908 and also to redesign the technical regulations. A maximum bore of 155 mm and a minimum vehicle weight of 1100 kg were now stipulated. At the same time, the use of the innovative Rudge Whitworth wheel hub developed in England, which made it possible to remove a wheel as a whole from the vehicle, was banned - a clear advantage over the removable rim rings from Michelin, which were first used in 1906 and had given the domestic participants a clear competitive advantage.
The race on 7 July 1908 was turbulent right from the start because, as in the two previous iterations of the Grand Prix, wheels and tyres played an important role in deciding victory or defeat in 1908 too. It also quickly became apparent that the Mercedes in particular had not only increased their speed, but were also demonstrating impressive reliability, while the vehicles from other manufacturers were increasingly struggling with technical problems. Nevertheless, it was truly a sensation when the young Christian Lautenschlager crossed the finish line as the winner after a race duration of 6 hours and 46 minutes and no fewer than 11 wheel changes. Following less than 10 minutes behind were two drivers from the Benz & Cie factory team, Victor Hémery and René Hanriot, in second and third place. Willy Pöge in the second Mercedes finished fifth; Otto Salzer had to retire after two laps with a defective wheel rim.
The result of the Grand Prix de l'A.C.F. was a nightmare for the French car manufacturers, who had become so used to success: only one of the seven first-placed cars bore one of their badges; the other six were from Germany. After a long dry spell, DMG in particular had benefited from the elaborate and meticulous preparation of the Mercedes racing cars and the high level of commitment of all those involved. The internationally acclaimed victory in Dieppe subsequently gave a considerable boost to the Untertürkheim-based company's reputation, as it impressively demonstrated the performance and reliability of the Mercedes racing cars.
The article in the Vienna edition of the "Allgemeine Automobil-Zeitung" of 19 July, in which the trade magazine "Auto" is quoted, also bears witness to this: "Let us not forget that we are dealing with a first-class company whose workshops have often been the birthplace of automotive progress. Today we are allowed to say it: for a while, it seemed as if the heads of the Mercedes brand were somewhat neglecting the sporting manifestations. More than once, the brand sent cars into the race that were not sufficiently au point and were ready to race far too late; the race organisation also often seemed a little haphazard. There was no sign of any of this today. [...] This whole little world, drivers and mechanics alike, showed such discipline and such combativeness and such eagerness to win that I realised how right Théry was when he told me that day: the one I'm most afraid of is Mercedes."