In 1949, BMW obtained permission from the Allies to build a motorcycle larger than 250cc. The R51/2 was thus born from the evolution of the pre-war R51/1.

On the engine side, it is that of the R51/1 with its two camshafts, but it has undergone some improvements, R25 cylinder heads but with more inclined carburetors to find the new central air filter. On the chassis side, we find the sliding rear suspension and the hydraulic telescopic fork which is now modeled on that of the R75G.

On the aesthetic side, the front mudguard is more enveloping and the headlight more profiled.

5000 copies were sold from 1950 to 1951, or over one year of production.