BMW R 57

The R57 had much in common with the R47 it replaced. Its engine featured the familiar 'square" bore and stroke at 68 millimeters and matched its predecessor's 18 horsepower output. However, there were some key evolutionary changes that affected the R57's performance. Key among them was an improved transmission and electrical system. This series of incremental improvements was not unlike the current evolution of the modern sportbike.

In 1928, Bosch improved the BMW boners' magneto ignition system with higher voltage and an optional generator to better power lights. The value of a strong ignition system cannot be overstated, considering the variable quality of fuel and state of tuning during the 1930s. Contrary to today's riders, motor-cyclists then were not required to have lighting nor did they necessarily desire it. BMW's sporting motorcycles were typically devoid of headlights or taillights emphasizing the no-frills aggressive nature of the sport-oriented machines, but by 1929, lighting was standard equipment on all BMWs.

To meet sidecar owners' needs, BMW's engineers gave the R57 a clutch update that incorporated two plates, rather than one in the dry clutch, like all BMWs. the R57 was also available with an optional shorter final drive ratio. Considering its sporting intent, the R57's chassis and suspension received some minor improvements to enhance the bike's handling. The wheelbase was shortened by 10 millimeters, and the fuel capacity was reduced due to a revised fuel tank shape. The front brake was enlarged to 200 millimeters, providing improved stopping power and compensating for the weak brake shoe at the rear wheel. Unfortunately, the R57's curb weight grew, which likely negated any performance gains to be had from the drivelinc and chassis refinements.

BMW produced about 1,000 R57 motorcycles, which was substantially less than the 1,700 R47 bikes to leave the factory. This was likely due to two factors: a 20 percent price premium over the outgoing R47 model and competition from the stout 750-cc side-valve R62. available for DM 1,650.