Model 20 500

1957 AJS Model 20 500 Technical Analysis & Specification Breakdown

Built around AJS's allround motorcycle platform, the 1957 AJS Model 20 500 pairs a 498 cc (30.4 cu in) air-cooled twin, four-stroke architecture with road-focused gearing. In factory specification, peak output is rated at 20 HP (14.6 kW) at 6,800 rpm, transferring power to the rear wheel through chain final drive. With a specific output of 40.2 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 Model 20 500 measures 178 kg (392 lbs) dry, translating to a power-to-weight ratio of 0.11 HP/kg (8.9 kg per horsepower). The 13.5-liter (3.6 US gal) fuel tank supports practical everyday commuting and weekend road stints, while factory top speed is listed at 137 km/h (85 mph).

Within MotoLibrary's AJS archive, this model family spans 11 indexed model years from 1949 to 1959, allowing buyers to track year-over-year changes in emissions tuning, weight and equipment.