60 Greatest Bikes: Ariel Square 4 Mk2

Published: 04 March 2015 Updated: 04 March 2015

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Ariel’s Square 4 – affectionately dubbed the ‘Squariel’ – had a lengthy production run stretching from 1931 to 1959 but the classic Mark 2 model was only built during the between 1953 and 1959. The Mark 1 had made 35bhp and had a top speed of over 90mph but the improved Mark 2 featured a re-designed cylinder head with four separate exhausts and the bike, with power upped to 40bhp, was now good for a genuine 100mph – but at almost £337, that improved performance didn’t come cheap.

Year: 1956
Manufacturer: Ariel
Model: Square 4 Mk2
Claim to fame: The ‘Squariel’ boasted the first square-four engine in a production motorcycle
Did you know? Engine designer Edward Turner first offered his Square 4 concept to BSA but it was rejected

Ariel’s Square 4 is significant because it was the first production motorcycle to feature a square-four engine design – a concept later put to devastating use by Suzuki with their two-stroke RG500 race (and road) bikes. Famed engine designer Edward Turner had come up with the concept of a square-four engine as far back as 1928 – essentially a pair of across-the-frame parallel twins – and had offered his design to BSA but was rejected. When Ariel accepted the design, Turner and the Square 4 entered the motorcycling history books.

Ariel actually made a prototype of a Mark 3 in 1954, complete with plush Earles suspension, but the bike never made it into production and the Square 4 – along with all other four-stroke Ariels – was discontinued in 1959 to make way for new two-stroke models.

To mark 60 years of publication, we are proud to prompt maybe the most controversial debate yet!

Between now and the end of the year we will keep the argument, over which of these bikes is the best that we’ve seen over our sixty years, raging and we want you to get involved. Cast your vote, send in tales and pictures as you make a case for your personal favourite.

By MCN

The voice of motorcycling since 1955