1937 BMW R12
A brief history of the R12.
BMW had a big problem in 1926: In sidecar service, their frames were cracking at the welds. It was necessary to design a completely new frame -- and while they were at it a completely new motorcycle in order to cure it.
The new frame was stamped out of heavy sheet metal in left- and right-channel section halves, and then cross-braced and joined with large round head rivets. Called the "star" frame, it could take the heavy bending loads of a sidecar without fatigue. It was also the forerunner of the modern perimeter motorcycle frame.
The new 750cc engines were the largest and most powerful yet produced by BMW, a 16 horsepower sidevalve, and a 28 horspower OHV version. The front suspension was a trailing link unit with stamped metal forward-sweeping forks, and linkage rods to a leaf spring, which extended over the front fender.
The R11 sidevalve "touring" model and the R16 OHV "sports" model were immediately successful both in solo and sidecar flavors.
By the middle of the 1930s, all of Germany was heady with technological achievement under the National Socialist government, and BMW asserted its superiority by setting land speed records (eventually reaching 179 mph in 1936), and competing in international roadraces. In spite of reaching nearly 100 horsepower with their supercharged 500cc engines, victory in roadracing eluded them. The evil handling of their chassis, and especially of their trailing-link forks, was the culprit.
By pouring resources on the problem, a solution was found: The telescopic fork. These forks were not the first to use the telescopic principle, but were certainly the first to be fully modern in design, with an internal hydraulic damping piston and valves to control both the compression and rebound rates.
The new forks were so superior to the old that in 1935, the R11 and R16 were fitted with them and given a little facelift and a 4-speed gearbox, thus producing the wildly successful R12 and R17. These were the first production motorcycles to use a modern front suspension, though they lacked any rear suspension at all.
This machine is owned by the author, and was restored to its present condition over a period of three years. Although the control layout takes a bit of practice -- its a right-side handshift with left-hand clutch -- it is an excellent runner. (Shifting goes like this: First, you close the throttle and take your hand off it, grab the shift knob and change gears. You then reach back up to the bar and grab the throttle again. If you do it quickly and with great coordination, you can get a fairly smooth shift because of the gigantic flywheel. It doesn't spin down very fast, and you can catch it at just the right RPM for the upshift. Downshifting is a true bitch. But that's the layout. Right-hand throttle and brake lever. Left-hand clutch and timing lever. Right-hand tank shifter. Right-foot heel-operated brake. Left foot does nothing at all, other than hold you up at stoplights.) Handling is quite good, although it must be forced into corners due to the sidecar-capable front geometry.
BMW finally solved its metal joining problem in 1936 by the introduction of electric arc welding, the R12 went on to be BMW's most produced model until the R75/5 of the early 1970's. Nearly 30,000 of them were made, 20,000 as civilian models (most of which were conscripted in 1939), and another 10,000 specifically built for the Wehrmacht.
BMW R12s did yeoman service in the German Army of WWII, but were eventually replaced by a purpose-built military model, the R75, in 1942. In addition to the messenger and scout roles that motorcycles played in the Allied armies, the Germans equipped motorized infantry regiments with R12 sidecar rigs and made war with them. The motorcycle units were the fastest in the blitzkrieg, and saw combat from the steppes of Russia to the deserts of North Africa.
Today, R12's are still in operation all over the world, including about 30 examples in the USA. Used, original, and reproduction parts are available from several German sources, and small numbers of machines have recently appeared from former iron-curtain countries.