Ingenuity or deception
The use of a petrol or oil tank as a motorcycle frame member was developed before the First World War, but didn’t often make it into production, or, if so, production was limited.
Denmark’s Nimbus is a good example of a vintage machine employing its petrol tank as part of the frame structure, in this case serving as the frame’s spine. Peder Anderson Fisker and H M Nielson founded their business in 1906 to make electric motors, with Fisker turning his hobby into his business. Fisker was the ideas man, leading to the Nilfisk vacuum cleaner in c1910 and, later, after two years’ development, their first motorcycle, the Nimbus, with an inline four-cylinder 746cc inlet over side exhaust valve engine mounted in a spring (either side) controlled swinging arm frame.
With hand change gearbox and shaft final drive, the Nimbus’s overriding feature was its frame’s main section, which was, in effect, a large diameter tube serving as the petrol tank with attached steering head and rear frame mountings, to which the duplex, under-engine, pressed-steel subframe fitted.
Just over 1000 of these machines were built 1919-1928, with Nimbus relaunching in 1934 with a revised model, featuring a riveted pressed-steel frame and separate fuel tank. Danish wags nicknamed the earlier machine the Nimbus ‘Kokkenror’ – kokkenror meaning ‘stovepipe.’
Although the Nimbus trend of using the petrol tank as a stress member never gained huge popularity, the idea surfaced on some limited production trials machines, for a few grasstrack frames and other
