BMW R75
The BMW R75 is a World War II-era motorcycle and sidecar combination produced by the German company BMW. The BMW R75 stands out by its integral two-wheel drive design, with drive shafts to both its rear wheel and the third side-car wheel, from a locking differential, as well as a transfer case offering both road and off-road gear ratios, through which all four and reverse gears worked. This made the R75 highly manoeuvrable and capable of negotiating most surfaces. A few other motorcycle manufactures, like FN and Norton, offered optional drive to sidecars. History . In the 1930s BMW were producing a number of popular and highly effective motorcycles. In 1938 development of the R75 started in response to a request from the German Army. Preproduction models of the R75 were powered by a 750 cc side valve engine, which was based on the R71 engine. However it was quickly found necessary to design an all-new OHV 750 cc engine for the R75 unit. This OHV engine later proved to be the basis for subsequent post-war BMW flat-twin engined motorcycles like the R51/3, R67 and R68. The BMW R75 and the competing  Zündapp KS 750 were both widely used by the Wehrmacht in Russia and North Africa, though after a period of evaluation it became clear that the Zündapp was the superior machine. In August 1942 Zündapp and BMW, on the urging of the Army, agreed upon standardization of parts for both machines, with a view of eventually creating a Zündapp-BMW hybrid (designated the BW 43), in which a BMW 286/1 side-car would be grafted onto a Zündapp KS 750 motorcycle. They also agreed that the manufacture of the R75 would cease once production reached 20,200 units, and after that  point BMW and Zündapp would only produce the Zündapp-BMW machine, manufacturing 20,000 each year. Since the target of 20,200 BMW R75's was not reached, it remained in production until the Eisenach factory was so badly damaged by Allied bombing that production ceased in 1944. A further 98 units were assembled by the Soviets in 1946 as reparations. Nevertheless, the standardization program achieved 70% parts commonality between BMW and Zündapp machines. This simplified the supply of spare parts for these vehicles, many of which are still in the hands of historic motorcycle enthusiasts. These vehicles are still highly desirable  as collector's items because of their elaborate and durable technology, and are correspondingly expensive. A well-restored R75 can still be used for everyday purposes, on or off-road without problems. During World War 2 the Soviet Union quietly purchased five units of the R-71 (the R-75's predecessor) via Swedish intermediaries to study and subsequently build their own version, the M-72, which Stalin approved for production. A Chinese variant of the M-72, the Yangtze River 750, has been in production since 1957. In 1954 a small number of modified R75 models were produced at Eisenach (then in Soviet -controlled East Germany) for testing under the designation AWO 700, but were not put into full production. The success and reliability of the shaft-driven R75 during the war led to the US Army requesting that Harley-Davidson produce a similar shaft-driven motorcycle for American troops. This led to Harley producing their first ever shaft-driven model, the Harley-Davidson XA, which was a near duplicate of the R75 without sidecar.