5. Ariel

Ariel Square 4-9

Like many defunct British motorcycle OEMs, Ariel was at one time a technological innovator. Legendary motorcycle designer Edward Turner designed the original Square Four for Ariel after joining the company in 1928. The unique engine incorporated a chain-driven overhead camshaft with two 180-degree cranks geared together and featured a unit transmission. The original model was a two-pipe design until the 1953 Mark II model switched to the four-pipe design picture above. Ariel was absorbed by BSA in 1958 and, as with most UK motorcycle manufacturers, came to untimely end in the latter part of the 1960’s decade.