R51

1938 BMW R51 Technical Analysis & Specification Breakdown

Engineered by BMW for the allround motorcycle segment, the 1938 BMW R51 pairs a 494 cc (30.1 cu in) air-cooled two cylinder boxer, four-stroke architecture with road-focused gearing. In factory specification, peak output is rated at 24.1 HP (17.6 kW) at 5,600 rpm, transferring power to the rear wheel through a 4-speed gearbox and shaft drive (cardan) final drive. With a specific output of 48.8 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 R51 measures 182 kg (401 lbs) wet (curb), translating to a power-to-weight ratio of 0.13 HP/kg (7.55 kg per horsepower). Rider ergonomics and chassis geometry center around a 1,400 mm (55.1 in) wheelbase engineered for quick, flickable steering geometry. The 14-liter (3.7 US gal) fuel tank paired with a rated consumption of 4 L/100 km provides an estimated theoretical range of roughly 350 km (217 miles) between fill-ups, while factory top speed is listed at 140 km/h (87 mph).

Within MotoLibrary's BMW archive, this model family spans 3 indexed model years from 1938 to 1940, allowing buyers to track year-over-year changes in emissions tuning, weight and equipment.