Built around NSU's sport motorcycle platform, the 1940 NSU 251 OSL pairs a 242 cc (14.8 cu in) air-cooled single cylinder, four-stroke architecture with road-focused gearing. In factory specification, peak output is rated at 10.5 HP (7.7 kW) at 5,200 rpm, transferring power to the rear wheel through a 4-speed gearbox and chain final drive. With a specific output of 43.4 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 251 OSL measures 126 kg (278 lbs) dry, translating to a power-to-weight ratio of 0.08 HP/kg (12 kg per horsepower). Rider ergonomics and chassis geometry center around a 1,285 mm (50.6 in) wheelbase engineered for quick, flickable steering geometry.
Within MotoLibrary's NSU archive, this model family spans 8 indexed model years from 1933 to 1940, 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.
Weight
Compare weight carefully because it affects low-speed handling, parking and confidence.
Brakes
Brake setup is worth comparing if you ride in traffic, mountains or with a passenger.
Transmission
Transmission and final drive affect maintenance, smoothness and everyday usability.
