The first Ariel Square Four 4F was presented in 1930, having an engine of 500cc. In 1931, the engine grew to 601cc. The year 1937 came for the Square Four with a changed engine with a displacement of 995cc, whose production lasted till 1949. At the beginning of the '50's, a Square Four I with 35bhp at 5500rpm was produced. This bike was able of running with 90mph. Its brother, the Square Four Mark II, built from 1953 to 1959 had the same 997cc engine and its speed was of 100mph. In 1954 there was a Mk3 prototype which, unfortunately, never saw the roads. After this experiment, the Square Four production ceased in 1959.
