Simson was a German company which produced firearms, automobiles, bicycles and motorcycles, and mopeds. In 1955, the year that the 425 S motorcycle was launched and the Simson brand name was restored, the factory also began making two-stroke mopeds.
The 425S was a single cylinder 250 cc of 15.5 hp, four stroke, shaft drive with better suspension and handling. The first model was the SR 1, a 48 cc machine producing 1.5 bhp.
This was succeeded by the SR 2 in 1957 and the SR 2E in 1959.The original 425 model had plunger rear suspension, a 6.7:1 compression ratio, produced 12 bhp and had a top speed of 100 km/h (62 mph).
The 425 S had a twin-shock swinging arm rear suspension and a top speed of 110 km/h (68 mph).It had 18 in (460 mm) wheels with 180 mm (7.1 in) full-width drum brakes to give it better acceleration and braking than the plunger model./wikipedia