Check the great Motart blog here
"The Imme R100 was a lightweight motorcycle produced from 1948 to 1951 by Riedel. The beauty of the machine is in it's sheer simplicity: due to constrained material and financial supplies, the front forks and swinging arm are single sided, the exhaust acting as the swinging arm member with the rear wheel being cantilevered with the engine, the tubing used for the frame, headstock, fork and arm are all the same 40mm diameter, the 3-speed hand change gearbox does not have a neutral position and the barrel and head for the 99cc engine producing 4.5BHP are one piece.
Oddly, first gear is in the middle of the shift pattern with second below and third above, with a mechanism to hold the clutch open when the engine idles in first. Norbert Riedel was able to secure materials for production from the americans after the war as the engine used in the R100 is the same as he designed to start the turbines on MeschMesserschmitt Me 262, which they were keen to acquire. Approximately 12,000 Immes were produced before the company folded in 1951, when a improved 150cc version was nearing production. Now rare and sought after machines this example was sold by Yesterdays recently."