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 Velocette - Roarer (compresseur)
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Velocette D2-492-44-01
Photo ou archives : J-P. Praderes

Capacity : 500
Model : Roarer (compresseur)
Production : 1939 -
Category : (R) Racing


500 Roarer Supercharged Twin -1939

Unfulfilled promise

The Veloctte Roarer was a casualty of WWII. Conceived in late 1938 by designer Harold Willis, it was constructed during the spring of 1939. It only ran in practice for the 1939 TT, and the postwar ban on superchargers brought an end to its career. This unique British attempt to strike back at BMW might have given Velocette the same dominance at the highest level that it already enjoyed with its KTT clubman racer.

Geared Crankshafts

Designed in parallel with a twin-cylinder tourer, the Roarer had nothing in common with the road-going machine save the original layout of its engine, which had two transverse crankshafts geared together for perfect balance. Each cylinder had its own independent single overhead-camshaft driven from a common kingshaft. Cylinders and cylinder heads were of aluminum and the crankcase was entirely made of magnesium.

Enormously Flexible

The supercharger, built into the rear part of the engine unit, fed the cylinders at the front by two backward-sloping intake pipes whose length ensured tremendous engine flexibility. The transmission shaft - chosen to prevent oil from getting onto the rear tire – ran inside the swing arm of the rear suspension in the most modern manner. The planned telescopic forks had been replaced, at the request of Stanley Woods, by a classic girder fork. Tried over the TT course during the 1939 practice session, the Roarer showed its immense potential. It steered like a dream and was turbine smooth.


Engine: 496cc (68x68mm) air-cooled twincylinder four-stroke; dry-sump lubrication

Power Rating: 54 hp @ 7000 rpm

Valves: overhead-camshaft driven by shaftand- bevel gearing

Fuel System: supercharger and carburetor

Transmission: 4-speed, multi-disc clutch; shaft final drive

Suspension: Webb girders (front); swing arm

with twin Dowty oil dampers (rea r)

Brakes: 10 inch drum (front & rear)

Wheels: wire (front & rear)

Weight: 370 lb

Maximum Speed: 145 mph


The legendary Roarer is once again in running order, thanks to an extensive restoration by marque specialist Ivan Rhodes.


Motorcycle encyclopedia Moto Passion, realised by François-Marie Dumas, include almost 2000 photos presented with an exhaustive history of the motorcycles exhibited.

This unique collection has been realised with the participation of many specialists. With many thanks in particular to Yves Campion, Michael Dregni, Didier Ganneau, Jean Goyard, Helmut Krackowizer, Michel Montange, Christian Rey, Bernard Salvat, Mick Woollett, etc

One can order here

  • Original cards on paper (in french)
  • High resolution scans or original documents presented and signed with my name.

Please contact me at for conditions and copyright.

© Tous droits réservés
François-Marie Dumas

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