The 166 MM grew directly from the Ferrari 166 S, itself an evolution of the original 125 S racer. Both shared the tube frame and double wishbone front/live axle rear suspension layout designed by Aurelio Lampredi, with a wheelbase of 2,420 mm. The key change from the earlier 125 S was the engine: the original 1.5-litre Gioacchino Colombo V12 was enlarged to a 2.0-litre (1,995 cc) unit by increasing bore and stroke to 60 by 58.8 mm. In 166 S trim, three carburetors produced 110 to 130 PS at 5,600 to 6,500 rpm and a top speed of around 170 to 215 km/h. For the MM variant, output rose to 140 PS at 6,600 rpm and maximum speed reached approximately 220 km/h.
The designation "MM" stood directly for Mille Miglia, the grueling Italian open-road endurance race, reflecting where Ferrari expected to prove the car's worth. A total of 47 Ferrari 166 MMs were produced between 1948 and 1953, compared with just nine 166 Spyder Corsas and three 166 Sports. The majority of 166 MM bodies were built by Carrozzeria Touring in their distinctive barchetta (little boat) form — open, lightweight aluminium shells with sweeping fenders that became one of the defining shapes of postwar Italian motorsport.
The 166 variant first established Ferrari's credentials at prestigious events even before the MM designation became standard. The 166 S won the 1948 Targa Florio in the hands of Clemente Biondetti and Igor Troubetzkoy, then Biondetti also drove a 166 S to victory in the 1948 Mille Miglia alongside Giuseppe Navone. In 1949, Biondetti and a co-driver won the Targa Florio again in a 166 SC.
The 1949 season belonged to the 166 MM in historic fashion. At the Mille Miglia, Ferrari 166 MM Barchettas scored a 1-2 result: Biondetti and Salani won outright, with Bonetto and Carpani second. The car then crossed to France for the 24 Hours of Le Mans, where Luigi Chinetti and Lord Selsdon drove a 166 MM to an outright victory. Combined with the Targa Florio success earlier in the year, this meant the 166 variant had won all three of the most prestigious road-racing events in a single season — a feat that has never been matched.
Further victories followed. Another 166 won the 1949 Spa 24 Hours, adding Belgian honours to the car's record. In 1950, a 166 chassis fitted with the larger 195 S engine won the Mille Miglia again, driven by Giannino Marzotto and Marco Crosara. The 166 MM was eventually superseded by the 2.3-litre 195 S as Ferrari's production line continued to develop.
The Touring barchetta body was the most celebrated of the 166 MM's several coachbuilt forms. Its rounded, uncluttered lines, open cockpit, and minimal windshield became synonymous with early postwar Italian sports car aesthetics. Carrozzeria Allemano built the first two 166 S cars, and Carlo Anderloni at Touring was responsible for the majority of subsequent bodies.
One particularly notable 166 MM, chassis 0018M from 1949, received an unusual Panoramica-style body by Zagato, very similar to a one-off Maserati A6 1500 also designed by Vieri Rapi; it is considered the first Ferrari coachbuilt by Zagato. It was later rebodied as a Zagato Spyder, and the original body was recreated in 2007 as part of Zagato's Sanction Lost programme.
Several 166 MMs survive in significant collections. The oldest Ferrari with an undisputed pedigree is serial number 002C, a 166 Spider Corsa (originally a 159) owned and driven by James Glickenhaus. Serial number 0052M, a 1950 166 MM Touring Barchetta, was discovered in a barn and publicly revealed for the first time since 1959 in the August 2006 issue of Cavallino magazine.
The Ferrari 166 MM defined what a postwar Italian sports racing car could be. Its 1949 campaign — Mille Miglia, Le Mans, Targa Florio — was the foundation on which Ferrari's entire identity as a race-winning manufacturer was built. The car's barchetta shape influenced Italian sports car design for a generation, and its V12 engine architecture foreshadowed the long line of Ferrari competition engines that followed. No subsequent Ferrari model has matched the 166 MM's feat of winning all three of those classic events in a single year.