The Ferrari 125 S (commonly 125 or 125 Sport) was the first vehicle produced and built by automaker Ferrari of Modena, Italy. Although preceded by Enzo Ferrari's Auto Avio Costruzioni 815 of 1940, the 125 S was the first vehicle to bear the Ferrari name when it debuted on May 11, 1947 at the Piacenza racing circuit. Like the 815, it was a racing sports car, but unlike its Fiat-powered 8-cylinder predecessor, the 125 S featured a V12 engine (the "125"), a trait it shared with most Ferrari cars of the following decades. The 125 S was replaced by the 159 S for 1947.
The 125 S used a steel tube-frame chassis and had a double wishbone suspension with transverse leaf springs in front with a live axle in the rear. Hydraulic power drum brakes were specified front and rear.
The 125 S was powered by Gioacchino Colombo's 1.5 L (1497 cc/91 in³) 60° V12 with a bore/stroke of 55 x 52.5 mm . This engine produced 118 bhp (87 kW) at 6,800 rpm with a compression ratio of 9.5:1. It was a single overhead camshaft design with 2 valves per cylinder and three double-choke Weber 30DCF carburettors.
Enzo Ferrari wanted the 125 S to use a five-speed gearbox as it matched the high revving V12 better than that of a traditional four-speed gearbox.
Both of the two 125 S cars built in 1947 were dismantled, and their parts are thought to have been re-used in production of the 159 or 166 models.
Recently, the chassis with serial number 010I was used in the restoration of a 125 S. It is rumored that 010I is actually s/n 01C. The story goes that 01C was re-stamped as 010I, and sold to a customer as a new car. Upon taking receipt of the car, the new owner immediately exclaimed, muletto!, which means "Test mule" in Italian, as he could clearly see that his supposedly new car was in fact a used, well-raced car. Ferrari made a new invoice for the car, including a considerable rebate given the car's second-hand nature.
Still in 166 Spyder Corsa configuration, the car was recently sold to Symbolic Motors. Close inspection of the chassis and its serial number led to the discovery of an old stamping that could possibly read 01C. It had been covered by an aluminum plate which bore the serial number 010I. Subsequently, the car was sold to its current owner, who refitted the chassis with a body similar to the factory's 125 S replica, which was built by Michelotto in 1987. The alleged 01C made its public debut at the Pebble Beach Concours d'Elegance, and was entered as a "Ferrari 125 S". The car continues to be the subject of much debate among Ferrari historians and enthusiasts; recent developments indicate that the restamped serial number was in fact a correction and not an alteration.
The 125 S debuted at the Circuito di Piacenza, driven by Franco Cortese, but was unable to finish the race, despite a favorable showing against the strong Maserati 6CS 1500s.
Two weeks later, the 125 S claimed Ferrari's first victory at the Grand Prix of Rome on the Terme di Caracalla Circuit, where it was also driven by Cortese. The car had spun a bearing in practice, and was repaired in the shop of Tino Martinoli, who later came to America with the Ferrari Indy car team.
The 125 S won six of its fourteen races in 1947, though drivers Clemente Biondetti and Giuseppe Navone were unable to win the 1947 Mille Miglia in it.