1957 Douglas Dragonfly Technical Analysis & Specification Breakdown
Positioned in Douglas's sport motorcycle lineup, the 1957 Douglas Dragonfly utilizes a 348 cc (21.2 cu in) twin, four-stroke layout. In factory specification, peak output is rated at 17 HP (12.4 kW) at 5,500 rpm, transferring power to the rear wheel through chain final drive. With a specific output of 48.9 HP per liter, the engine character is prioritizing low-RPM tractability, mechanical longevity and relaxed throttle response over peak redline numbers.
On the scales, the Dragonfly measures 166 kg (366 lbs) dry, translating to a power-to-weight ratio of 0.1 HP/kg (9.76 kg per horsepower). The 25-liter (6.6 US gal) fuel tank supports practical everyday commuting and weekend road stints.
Within MotoLibrary's Douglas archive, this model family spans 3 indexed model years from 1955 to 1957, allowing buyers to track year-over-year changes in emissions tuning, weight and equipment.
Specific Output
48.9 HP/L
Power-to-Weight
0.1 HP/kg (9.76 kg/HP)
Engine
Displacement348.0 ccm (21.23 cubic inches)
Engine TypeTwin, four-stroke
Engine DetailsTwin, four-stroke
Power17.0 HP (12.4 kW)) @ 5500 RPM
Fuel SystemCarburettor
Fuel ControlOverhead Valves (OHV)
IgnitionCoil
Transmission
Final DriveChain (final drive)
Chassis
Frame TypeTubular duplex cradle
Front SuspensionLeading link
Rear SuspensionHydraulic shock absorber
Wheels & Brakes
Front BrakesExpanding brake (drum brake)
Rear BrakesExpanding brake (drum brake)
WheelsSpoked
Dimensions & Weight
Dry Weight166.0 kg (366.0 pounds)
Power/Weight0.1024 HP/kg
Fuel Capacity25.00 litres (6.61 US gallons)
Buying Checklist
Before You Compare This Bike
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.
Weight
Compare weight carefully because it affects low-speed handling, parking and confidence.
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.
