1939 BMW RS 255 Kompressor
Claimed power: 55-60hp @ 7,000 rpm
Top Speed: 100mph (est.)
Engine: 492.6cc air-cooled DOHC horizontally-opposed 2-cylinder flat twin, 66mm x 72mm bore and stroke w/Zoller supercharger
Weight (dry): 302lb (137kg)

When German BMW rider Georg Meier took the checkered flag in the Senior Tourist Trophy race at the 1939 Isle of Man, it marked the first time a non-Briton had won since the beginning of the TT in 1907.

Meier won the race aboard the exact 500cc BMW RS 255 Kompressor featured here, clocking an average speed of 89.38mph and finishing in two hours, 57 minutes and 19 seconds, a full two minutes ahead of his closest competition, BMW teammate Jock West.

Supercharging

Meier’s win was the culmination of years of development. In the mid 1920s, BMW began experimenting with supercharging — mechanically forcing more air into an engine. Simply put, more air allows more fuel to be burned, increasing the overall output of an internal combustion engine. BMW used Swiss-built Zoller superchargers, and according to author Darwin Holmstrom in his book BMW Motorcycles, these early units, which sat over the transmission connected to the crankshaft by a separate shaft, nearly doubled power output over a normally aspirated engine.

By 1935, BMW’s engineers had moved the supercharger to the front of the engine. The 500cc race engine now featured twin overhead cams driven by side shafts, and a new left side, foot-shift, 4-speed gearbox. With the addition of rear suspension in 1937, BMW’s race bikes handled significantly better than before, and their 500cc race team was winning competitions.

Georg “Schorsch” Meier, who had previously competed off-road, moved to the track in 1938 and took both European and German Championships aboard the BMW RS 255 Kompressor. But the team’s success didn’t follow them to the Isle of Man. During the 1938 Senior TT, teammate Karl Gall wrecked during practice, and his injuries kept him from participating in the race. Then Georg retired on the first lap in the race because of a faulty spark plug. The only saving grace for BMW was Jock West, who finished fifth, one spot better than his 1937 finish.

Prepared to win

In 1939 BMW arrived at the island early and well prepared. Meier, quoted in a story on the BMW Group Press Club USA site, said, “With BMW’s small racing department we arrived in Douglas in good time, since the official practice sessions started 14 days before the race. Early in the morning, at the break of dawn, we were already out there on the roughly 60 kilometre-long island track where people claimed that ‘only an English rider was able to win the race.’ And believe me, the circuit with all its substantial challenges really demanded the utmost of the rider.”