The 125 F1 shared its name with the 125 S sports racer, which preceded it by a year but was developed concurrently. Initially, the racing car was known as the 125 GPC, standing for Gran Premio Città or Grand Prix Compressore, before the formal establishment of the Formula One era.
The 125 F1 was built around a steel tube-frame chassis featuring longitudinal and cross members. Its suspension system included a double wishbone with a transverse leaf spring at the front, and a torsion bar at the rear, which was upgraded to a de Dion tube for the 1950 season. Steering was managed by a worm and sector system, and it utilized four-wheel drum brakes, which were standard for the period. The initial wheelbase of 2,160 mm was extended to 2,320 mm in the 1949 redesign. Valerio Colotti was responsible for the chassis and transmission design.
Powering the 125 F1 was Colombo's 1.5-litre (1497 cc) V12 engine. The engine's and the car's name, like the 125 S sports racer, were derived from its 124.73 cc cylinders, measuring 55 mm by 52.5 mm. It featured a single overhead camshaft on each bank of cylinders, arranged at a 60° angle between the two banks. The engine had two valves per cylinder, fed by either one Weber 40DOC3 or 50WCF carburettor. Despite a relatively low 6.5:1 compression ratio, the supercharged engine produced 230 PS (169 kW; 227 hp) at 7000 rpm. However, its Roots-type single-stage supercharger struggled to generate the high-end power needed to consistently challenge the eight-cylinder Alfa Romeo 158 and four-cylinder Maserati 4CLT. Despite this, the car's nimble chassis and strong driving performances allowed Ferrari to achieve a third-place finish in its inaugural race.
For the 1949 season, the engine underwent further modifications, incorporating dual overhead camshafts (while retaining two valves per cylinder) and a two-stage supercharger. These enhancements improved the car's top-end performance, boosting its output to between 260–280 PS (191–206 kW; 256–276 hp) and contributing to its five Grand Prix wins that year. Development continued into the following year, but the problematic superchargers were eventually abandoned in favor of larger displacement engines, with Lampredi's 275 engine superseding the original Colombo design.
The 125 F1 made its racing debut at the Italian Grand Prix on September 5, 1948. Three cars were entered for the event, driven by Prince Bira of Siam, Nino Farina, and Raymond Sommer. Sommer secured a third-place finish in the race.
The original chassis of the 125 F1 have been lost, having been repurposed for the Ferrari 275 F1. However, an exact replica, equipped with the original Colombo engine, is currently housed at the Museo Ferrari in Maranello, displayed alongside more contemporary Ferrari F1 machines.
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