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 OK Supreme - Grass track model
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OK Supreme D2-492-60-10
Photo ou archives : F-M. Dumas

Capacity : 500
Model : Grass track model
Production : 1937 - 1946
Category : (Off-Road) Speedway & other


500 Grass-Track - 1937

Speed on grass

In Great Britain, during the years before and after WWII, grass-track racing was one of the most popular forms of motorcycle sports. It was run over circuits of varying length that – unlike Speedway – had both right- and left-hand bends and could be traced out in any field where permission could be obtained, often incorporating steep ascents and descents. Brands Hatch, a Grand Prix circuit, started as a grass track in the 1930s.

Hotheaded ...

Many British makers built special grass-track machines. This OK-Supreme has a "five-stud" JAP 500 Speedway engine, so-called from the five studs retaining the cylinder head instead of the usual four. Since the high-compression Speedway units, running on methanol, had the tiresome habit of shedding their heads and grass-track circuits were longer than those used for Speedway, a gearbox was a useful addition.

Marque Supremacy

Ernie Humphries, who was a partner in the OK company, resigned in 1926 and moved into a new factory to build a new motorcycle -the "OK-Supreme." Alec Bennett designed a squish-type head for the works JAP-engined racers for the 1928 Lightweight TT, won by Frank Longman's OK-Supreme after Bennett retired. Though OK-Supreme built its own engines after 1930, it continued to use JAP power units and specialized in grass-track racers. In 1946, Humphries' son John built some promising 346cc OK-Supreme-JAP grass-track bikes. But John was killed in a fall from a hotel window, and his 90-year-old father could not carry on production.


Engine: 497cc (80x99mm) air-cooled single-cylinder four-stroke; total-loss lubrication

Power Rating: 42 hp @ 6,000 rpm

Valves: overhead

Fuel System: Amal carburetor

Transmission: 4-speed, chain final drive

Suspension: girder forks (front); rigid (rear)

Brakes: drum (front & rear)

Wheels: 3.00x21 inch (front); 3.50x19 inch (rear)

Weight: 298 lb

Maximum Speed: 90 mph

OK-Supremes lived up to their name in both grass-track

and speedway racing, ridden by Fred Hudson, Andy Mackay and John Humphries.

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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