CarBrandLogos archive · BSA · 1937

BSAM20

Slow, heavy, unbreakable — the despatch rider's bike of the Second World War.

The story

A defining chapter in BSA history.

Explore the ideas, engineering and context that shaped the BSA M20, then continue into its specifications and place in the marque's lineage.

Origins

The M20 was not admired when BSA introduced it in 1937. Its 496 cc side-valve single was already old-fashioned, producing modest power and hauling a heavy frame, and early War Office trials were unenthusiastic. What the tests eventually established was the quality that mattered more than speed: it would keep running when abused by riders with no mechanical training, on bad fuel, in mud, with minimal maintenance.

1937 BSA M20 · AlfvanBeem · CC0

Design and engineering

That made it the standard British military motorcycle. BSA supplied them to the armed forces in enormous numbers through the war — more than any other model from any British maker — for despatch riding, convoy escort and general communications duties. The specification barely changed: side valves, four-speed gearbox, chain drive, girder forks on wartime machines, rigid rear end.

In production

Production continued until 1955, with post-war civilian and export versions and long service with police forces and the AA. Surplus M20s flooded the British market afterwards and taught a generation to ride. It is a bike remembered less for what it was like than for how many of them there were, and how few of them stopped.

At a glance