Here as an interesting racer that came up for sale recently in Europe. It's an R75 (WWII military, not the /5 type) powered plunger frame sidecar rig. .
The front upper sidecar brace - which normally would attach to the sidecar frame just ahead of the cylinder, extends over to the far side of the rig, providing much stronger triangulation. An additional grab handle has also been installed on the brace. Note the use of the 1936 R5 trans, which has no air filter on top.
I'm not exactly sure what brand front forks are on this bike. The flat upper triple tree (visible in one of the other photos) suggested a pair of prewar BMW forks - but the fork legs change diameter about half way up, and I'm not familiar with any BMW forks that do that.
All-in-all a very nice looking rig. I never heard if it sold. There's another interesting old BMW in the building behind this bike. It looks to be an R51.
Another racer, this one an R51..
Note the use of the same transmission as the sidecar rig above.
Interesting looking cylinder fins - they look closer to the style used on the R66. Note the Hoske total loss timing cover on the front of the engine, and the tach drive takeoff at the end of the oil pump shaft drive (off the right camshaft).
Something you might expect to be fitted to a racer, here's a Schorsch Meier full width racing hub. I've seen very few of these are around. Someone in England was lucky enough to get these wheels on an R67/2 that they found. I missed a chance at buying a set of these a few years ago, because the bent spokes caused me to doubt that they were really for a BMW - it looked like an old 350 Honda front brake from this side! But this is correct for the Meier hubs.
Flip side view of the same wheel. Old timers tell me that they preferred the Hoske racing hubs to the Schorsch Meier hubs for two reasons: 1) The Meier hub was actually very heavy, so there is a weight penalty to use them; 2) The Schorsch Meier hubs were known to develop cracks.
Probably the FINEST restoration of an R68 that I have seen is this machine, which is owned by one of my web page readers here in the States. The paint work is by Kent Holt.