Ariel Square Four

Years produced: 1948-52 (Mk1)
Total production: 1,211
Claimed power: 34bhp @ 5,400rpm
Top speed: 100mph (est.)
Engine type: Overhead valve, air-cooled square four
Weight: 197kg (433lb)
Price then: $658 (1952)
Price now: $5,000-$9,500
MPG: 40-55

It's all so effortless that I can barely believe the bike I'm riding is half a century old. On the open road, the 1952 Ariel Square Four is at home in modern traffic in a way that most classic British motorcycles cannot approach. It purrs along smoothly at 60mph, accelerates briskly out of roundabouts with barely a need to use its slick gearbox, and feels more up-to-date and sophisticated than many bikes half its age.

Admittedly, this image of contentment is upset on occasions, notably when the feeble brakes are needed urgently, or when the bike runs out of ground clearance with a loud clunk even at modest angles of lean. But most of the time, riding this 1952 Ariel Square Four is a reminder that even in days long-ago, the British motorcycle industry was capable of building machines that could deliver good performance and comfort with a genuinely refined feel.

Squaring with history

The Ariel Square Four was one of the most glamorous and best known British motorcycles. In production for 27 years, it was a mainstay in Ariel's line of motorcycles.

Its story begins almost 80 years ago when, legend has it, a young engineer named Edward Turner — later to find fame as boss of Triumph — sketched a "square four" engined motorcycle on the back of a cigarette pack. Turner offered his design to a string of motorcycle manufacturers before being hired by Ariel in 1928.

Turner's innovative design featured chain-driven single overhead camshafts, and was effectively two parallel-twin engines with their crankshafts geared together and turning in opposite directions. This had the advantage of being not only very well-balanced but also compact, which allowed the original 497cc engine to be fitted to a slightly modified Ariel single-cylinder chassis, saving the firm from Selly Oak in Birmingham both money and development time.

Ariel launched the original 500cc Square Four in 1930 and added a more powerful 600cc version two years later, mainly for the benefit of the many owners who added a sidecar. But Turner's engine design had many problems, especially overheating of the rear cylinders. In 1937, after Turner had left Ariel, these problems were addressed by Val Page, another of the British motorcycle industry's most famous names, with a revamped pair of Square Fours in 600 and 1000cc capacities, known as the 4F and 4G, respectively.