1955 BSA M 21 Technical Analysis & Specification Breakdown
Built around BSA's allround motorcycle platform, the 1955 BSA M 21 relies on a 591 cc (36.1 cu in) single cylinder, four-stroke powerplant. In factory specification, peak output is rated at 15 HP (10.9 kW) at 4,000 rpm, transferring power to the rear wheel through chain final drive. With a specific output of 25.4 HP per liter, the engine character is prioritizing low-RPM tractability, mechanical longevity and relaxed throttle response over peak redline numbers.
The 11.36-liter (3 US gal) fuel tank supports practical everyday commuting and weekend road stints.
Within MotoLibrary's BSA archive, this model family spans 4 indexed model years from 1953 to 1956, allowing buyers to track year-over-year changes in emissions tuning, weight and equipment.
Use this page to compare this motorcycle by its real specifications, not only by model name. Focus on the details that affect fit, comfort, handling, range and ownership.
Power
Compare engine output with similar motorcycles if acceleration, highway use or two-up riding matters.
Fuel Capacity
Fuel capacity helps estimate touring range and how often you may need to stop.
Brakes
Brake setup is worth comparing if you ride in traffic, mountains or with a passenger.
Suspension
Suspension details can matter for comfort, road feel and long-distance riding.
