Ariel’s range for 1931 encompassed a dazzling variety of models: vertical engines, sloping engines, side valves, overhead valves – two or four per cylinder – all were represented along with Edward Turner’s revolutionary Square Four. Following the then fashionable trend, the SF31 was one of three half-litre ‘Sloper’ models that joined the range in the spring of 1931. Like that of its fellows, the newcomer’s overhead-valve engine was inclined at 30 degrees from the horizontal, conveying the benefits of better cooling, greater accessibility, and a lowered centre of gravity for improved handling. A twin-pipe exhaust system, exiting from a transverse silencer box ahead of the engine, was a particularly striking feature. Having completed many Durban to Johannesburg events, this wonderful bike offers great classic touring.