Mars A20 | Germany 🇩🇪, 1921.

The Mars A20 was an innovative motorcycle created in 1920. It featured a box-type frame with integrated fuel tanks, a longitudinally mounted horizontally opposed 956 cc (7.3 hp) engine with an external flywheel-fan, and an unusual two-speed gearbox: two internal friction drums with two chains per rear wheel, with hand and foot brake controls. It was produced until 1932, with just over a thousand units produced.