The Automobile Club de France (ACF) had been pushing to reduce engine sizes in racing for several years, citing increasing danger at higher speeds. For 1914 they mandated a maximum engine capacity of 4.5 litres, with cars required to fall within a weight range of 800–1,100 kg excluding fluids and tools. A maximum of five cars per manufacturer was permitted, with no privateer entries allowed.
Lyon offered substantial financial subsidies to host the race, and the chosen circuit ran clockwise for 37.6 km through public roads south of the city. The route passed through Vourles, along the Gier valley toward Châteauneuf, and returned on a long straight before a notorious steep downhill switchback nicknamed "le piège de la mort" — the Death Trap. The race was scheduled for twenty laps, totalling 752.6 km.
The field of 37 starters from 13 manufacturers and 6 countries was one of the strongest ever assembled for a Grand Prix. Peugeot arrived as strong favourites, seeking a third consecutive victory. Their new EX-5 car featured a 4.5-litre four-cylinder twin-overhead-cam engine producing 112 bhp, four-wheel brakes, and a streamlined extended tail. Team leaders Georges Boillot, Jules Goux, and Victor Rigal were each regarded among the finest drivers of the era.
Louis Delâge entered three cars for Albert Guyot, Arthur Duray, and Paul Bablot, while veteran Ferenc Szisz — winner of the inaugural 1906 Grand Prix — came out of retirement to drive for new French company Alva.
The most formidable challenge came from Mercedes. The German manufacturer had been absent from Grand Prix racing since their 1908 victory, but returned with a thoroughly prepared 4.5-litre car featuring a single-overhead-camshaft engine with four valves per cylinder producing 106 bhp at 3,100 rpm. In place of chain-drive they used a live rear axle. Crucially, the team had sent engineers to reconnoitre the circuit in January and calculated that their more durable Continental tyres — versus the Dunlops on the French cars — would allow just a single tyre stop per car. Five of the six 18/100 cars built were entered, led by Christian Lautenschlager, the 1908 winner, alongside Otto Salzer, Max Sailer, Louis Wagner, and Théodore Pilette.
The backdrop was already ominous: on 28 June — just six days before the race — Archduke Franz Ferdinand had been assassinated in Sarajevo.
Race day was hot, with some 300,000 spectators lining the roads. Cars were flagged off in pairs at 30-second intervals in numerical order, starting at 8 am.
Young Mercedes driver Max Sailer immediately forced the pace, drawing Boillot into a speed contest and setting the fastest lap on the fourth lap. Sailer had built a lead of almost three minutes over Boillot when his engine failed with a broken connecting rod on the sixth lap, ending his challenge beside the Gier River.
With Sailer out, Boillot led for much of the middle portion of the race, holding an advantage of two to three minutes over Lautenschlager. The fundamental problem for Peugeot, however, was tyre wear: while each Mercedes needed only one tyre stop, Boillot was compelled to make six pit stops for tyre changes. The streamlined tail that had been designed to improve aerodynamics also poorly distributed the weight of spare tyres, which had already caused handling problems during practice.
By the seventeenth lap, Lautenschlager had closed to within 14 seconds of Boillot. He overtook the Peugeot approaching Givors. Boillot continued to drive at the absolute limit with his car falling apart around him — reduced to running on three cylinders — and by the end of the eighteenth lap was 30 seconds behind. On the final lap his engine expired completely when he over-revved it climbing out of the Gier valley. Boillot was reportedly found hunched over his steering wheel in tears.
Mercedes took a crushing 1-2-3 finish: Lautenschlager first at an average of 105.7 km/h (65.7 mph), Wagner second, and Salzer third. Goux in fourth for Peugeot was nearly ten minutes behind. The French crowd received the result in silence.
Within a month of the race, Europe was at war. European Grand Prix racing did not resume for four years. Lautenschlager used his 25,000-franc prize money to build a house and retired from racing. Georges Boillot transferred to the French Air Force and was killed in aerial combat over Verdun in April 1916.
The race had lasting consequences beyond the result. The Mercedes engine's sophisticated valve train was studied closely by British engineers — one of the cars was sent to a London dealership before war broke out and commandeered for examination — and elements of the design reportedly influenced the Rolls-Royce Eagle aero engine used in Bristol fighter aircraft. American driver Ralph DePalma purchased one of the Mercedes Grand Prix cars and drove it to victory at the 1915 Indianapolis 500. Scrutineers also discovered post-race that the FIAT entries had exceeded the 4,500 cc engine limit, but FIAT's longstanding support of Grand Prix racing saw them escape formal disqualification.
The 1914 race is remembered as the last Grand Prix of the pioneering era, a masterpiece of preparation and strategy by Mercedes at the precise moment French dominance in racing appeared total, contested under the shadow of a war that would reshape the world.