Historic Motorcycle Brands
Nimbus
Nimbus was a Danish motorcycle produced from 1919 to 1960 by Fisker and Nielsen of Copenhagen, Denmark, who were also manufacturers of globally-sold Nilfisk-brand vacuum cleaners, from 1910. Two basic Nimbus models were produced powered by an in-house, 750cc, four-cylinder engine.
Off the back of profits generated by Europe’s first successful vacuum cleaners, Peder Andersen Fisker Fisker developed a motorcycle prototype of his own design.
The first Nimbus motorcycle had a 10bhp, four-cylinder, air-cooled, in-line engine of 746cc capacity, which featured automatic (suction) inlet valves and side exhaust valves. The cylinders were individually cast and had copious heat-soak finning.
Fisker decided the four-cylinder arrangement was desirable, as it could provide a good deal of torque at low rpm, meaning that neither high revs nor high horsepower were essential.
It drove the rear wheel via a three-speed gearbox with tank-mounted hand-change and shaft drive, rather than belt or chain drive commonly used at that time. It had a top speed of around 85km/h, with a sidecar fitted.
At a time when nearly all bikes had no suspension, the Nimbus boasted both front trailing-link suspension and rear swing-arm suspension.
The Nimbus’ frame was also revolutionary, featuring a large-diameter tubular upper section, to which twin cradles were attached. The result was a very stiff frame that was emulated by several later makers, including Egli.
The unusual upper frame tube also housed the fuel tank and its appearance soon earned the Nimbus the nickname of Kakkelovnsrør (‘Stovepipe’), because of the thick, round pipe between the saddle and handlebars.
Two production machines were constructed in 1919, but mass production did not begin until ‘Fisker & Nielsen’ became a limited liability company in 1920.
Disappointed by poor sales, Fisker began entering the Stovepipe in all the races that he could, often with a sidecar attached and soon established a good reputation for the machine.
In 1921, a Nimbus won the 1300-kilometre Paris-Copenhagen race and another tuned example scored an emphatic first place in the 1922 Odense-Berlin-Odense race, topping 140km/h and averaging an amazing 4.8L/100km in the process.
The ‘Stovepipe’ was technically improved along the way, mainly in details, but also with front fork variations, which distinguished the Type A from the Type B. The Type B had leading-link front suspension.
However, the introduction of a Danish sales tax on motorcycles in 1924 and an economic recession resulted in production being discontinued from 1926, after 1300 machines had been produced. The company concentrated on vacuum cleaners only, for six years.
With his son Anders, Fisker started designing a new machine in 1932 and in 1934 they demonstrated a new Nimbus motorcycle, the Type C. Anders had his eye on simplicity and price control, given the Great Depression-related circumstances.
Shaft drive was retained, but a completely redesigned engine was developed. It was a monobloc casting that incorporated an overhead camshaft, driven by a bevel-gear shaft that also powered the dynamo. Oddly, the crankshaft bearings were reduced from three to two, but the mains were large ball bearings, with pressure-fed lubrication.
The exposed valves were inclined in hemispherical combustion chambers, but there was no lubrication provided, so owners learnt to oil the valve stems occasionally! A low compression ratio was retained, to avoid overheating and to make kick-starting easier, so the output was only 18bhp.
The Type C frame was formed from rivetted, flat-strap steel that didn’t look very flash, but was easy to repair. It was curved to go around a conventionally-shaped fuel tank.
Front suspension was by sprung telescopic forks – a year before the BMW R12 adopted the design – but, where the R12’s forks had hydraulic damping, the Nimbus’ forks did not have hydraulic damping until 1939. However, the ‘upside-down’ Nimbus fork configuration preceded sports bike and racing bike front ends by around 60 years.
The sprung rear suspension was abandoned, because Danish road quality had improved in the 1930s, so a sprung saddle was the only rear suspension.
The Type C’s distinctive humming exhaust note led to it being nicknamed Humlebien (‘Bumblebee’) and the new bike soon became the best-selling motorcycle in Denmark.
A ‘tuned’ model with 5.7:1 compression ratio and foot-operated gear change was available in 1939.
The Danish Post Office, Army and Police purchased substantial numbers of the basic model and in 1939 as war loomed, the Danish Government motorised its army and many Type Cs were purchased.
During the occupation by German forces from 1940 to 1945, it was difficult for Fisker & Nielsen to obtain the materials needed for motorcycle production and only about 600 machines were made during the period. It’s also possible the company didn’t try too hard to help the Nazis.
Shortly after World War II, a 5.4:1 compression ratio engine was released, with an output of 22bhp, but only minor improvements were made to rest of the specification, usually making it possible to upgrade older models.
The Danish Army continued to buy around 20-percent of Fisker & Nielsen’s production, which no doubt influenced the decision not to introduce a new model, because the military would be unlikely to want an enlarged spares inventory.
The Postal Service bought many Type C models, using them as late as 1972. The Danish police force was also a large customer, but phased out its Nimbuses in the late 1950s and early 1960s, when they became too slow to keep up with modern cars and motorcycles.
In the 1950s some further prototypes were built, including a four-cylinder with a rotary valve and carbon seals as well as a two-cylinder model with sprung rear suspension, neither of which reached production. Several prototypes with sprung rear suspension and Earles front forks also were built.
Interest in practical motorcycles declined in the late 1950s – particularly those with sidecars – as a consequence of the availability of cheap cars such as the Volkswagen Beetle. More nimble Ariels and Zundapp motorcycles arrived on the Danish market, as well.
Nimbus production ended in 1959, when the last contract for the army was fulfilled.
The innovative Nimbus has iconic status, not only in Denmark but also abroad, where its very individual character makes it a machine of unusual technical interest.
Of around 12,000 Bumblebees produced, around 4000 are registered and running in Denmark and some hundreds are in Sweden, Germany and the USA.
Most mechanical parts are readily available as well as being relatively inexpensive.
ADVERTISEMENTS
