The 1925 Grand Prix season was a watershed year in motor racing. It was the first year for the new AIACR World Manufacturers' Championship season. The championship was won by Alfa Romeo, with its P2 model.
In January, the AIACR had settled on the championship format – four Grands Prix to be held in the US, Belgium, France and Italy (of minimum 800km length), with compulsory attendance of the Italian GP and the manufacturer's home race to qualify. The best three of the four results would count. It ran on the successful 2-litre formula already in place.
This year, the Targa Florio was a competition between the French teams of Bugatti and Peugeot as the major Italian teams did not enter. In a close race, the Peugeots initially led but it was the smaller Bugatti of Bartolomeo Costantini that came through for the victory. Louis Wagner was second for Peugeot, after he was delayed when stopping to assist his teammate, Christian d'Auvergne, who had been seriously injured in an accident.
Only a small entry lined up for the Indianapolis 500, dominated by Millers. Dave Lewis ran the new Miller – the first front-wheel drive car to enter the race. The Duesenberg challenge was led by the previous year's winner Peter DePaolo. From the start the Duesenberg teammates DePaolo and Phil Shafer set the pace. Just after halfway, DePaolo pitted suffering from blistered hands, taking relief from Norman Batten while the injury was attended to. Lewis in the FWD Miller got to the lead but was reeled in by DePaolo after he had gotten back in his car. Lewis in turn was substituted by Bennett Hill who had retired earlier. Although Hill charged hard, DePaolo held on and won by almost a minute, with Shafer third. It was the first time the race had been won in under 5 hours, averaging over 100mph. Pete DePaolo would go on to win the AAA championship.
The inaugural Belgian Grand Prix had only seven entrants with only the Alfa Romeo and Delage works teams starting. Then when all four of the French cars had retired by half distance, it left just Antonio Ascari and Giuseppe Campari circulating to give Alfa Romeo a 1–2 victory. The blue riband French Grand Prix did have a more complete entry list and was held on the recently completed full circuit at Montlhéry. Once again Ascari leaped into the lead until he misjudged a corner and crashed. Seriously injured, he died on the way to the hospital. When the news was announced the rest of the Alfa Romeo team was withdrawn. After that, Robert Benoist led giving Delage a 1–2 victory and becoming the first Frenchman to win his home Grand Prix since 1913.
The Italian Grand Prix was the final race of the championship. Alfa Romeo, Delage and Duesenberg had one win apiece but Delage chose not to contest it. Duesenberg entered two cars for Tommy Milton and Pete Kreis. Indianapolis winner Pete DePaolo also came across, taking the place of Ascari in the Alfa Corse team. Bugatti entered its new 1.5-litre models. Kreis in the Duesenberg led at the start but crashed on lap 3. The Alfas then set the pace but when they pitted for fuel Milton led until he was delayed with a slow pitstop. Brilli-Peri took a comfortable win by 20 minutes from Campari, thus giving Alfa Romeo the Manufacturer's Championship.
In the middle of the year, Germany was admitted into the AIACR, allowing German teams to enter the Championship in 1926. This was the last year of the current 2-litre formula. Increased concerns about the high speeds and safety led the AIACR change the regulations the following year to the 1.5-litre voiturette class for Grand Prix racing.
Manufacturers' World Championship
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Other Races
Major non-championship races are in bold
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Teams and drivers
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Significant Privateer driversNote: * was raced as a relief driver. Those in brackets show, although entered, the driver did not raceRegulations and Technical The AIACR (forerunner of the FIA) 2-litre regulations for Grand Prix races remained unchanged. In the United States, the American Automobile Association (AAA) stayed with the same regulations as well. The AIACR followed the American example to remove the mandatory mechanic on board, replacing him with a compulsory rear-view mirror instead. As the circuits used became shorter, as well as the danger to the passenger, the mechanic had become superfluous. Incongruously, the cars still had to be 2-seaters.