The other worrying moments of my test came every time I needed to put the bike on its stand. This is a rear-mounted contraption that requires the rider to walk to the back of the Square Four, keeping it vertical all the while, before putting down the stand and then heaving the bike backwards onto it. Not exactly easy to use, but at least the Ariel was very stable once on the stand.

Squaring off

This Four was one of the last of its type, because in 1953, the year after it was built, Ariel introduced an improved version—the 4G MkII. It incorporated a new cylinder head complete with four instead of two downpipes, and cooling was improved by air that now ran over the exhaust ports. Other changes included a new oil pump and a stronger dry clutch. Reshaped pistons helped increase power to 40hp at 5,000rpm, giving the Square Four a performance boost that lifted its top speed to over 105mph in some tests.

Even in 1956, Ariel continued to update the Squariel, with features including a full-width front drum brake, headlamp cowling and quick-detach rear wheel. There were prototypes with more substantial changes too, notably a MkIII that came complete with a twin-shock rear suspension. This was never produced. Nor, sadly, did Ariel ever get around to introducing the liquid-cooled engine that might have solved the Square Fours' overheating problem for good.

The reason for a lack of further development was simple: Ariel, by now part of the BSA group, had made its controversial decision to abandon four-stroke production in favor of the fully-enclosed Leader commuter bike. In 1958, the year the two-stroke Leader was launched, the four-cylinder bike was dropped from the range, and an era that had lasted for almost 30 years came to an end. Nobody who had experienced the Square Four's unique blend of performance, smoothness and sophistication would forget it. MC