This is from the site Bring a Trailer (https://bringatrailer.com/) ...
This 1948 Ariel Square Four is fitted with an interesting Watsonian sidecar, though the real point of fascination here is the bike’s unusual engine in which two vertical twins occupy the same case, with their cranks geared together to provide drive. The seller describes condition as original, though also admits to some restoration work–regardless of its history, condition looks truly excellent throughout. Find it here at Hyman in Saint Louis, Missouri for $42,500.
The Ariel looks to be in great shape, despite showing a few very minor nicks and other imperfections. The frame has been repainted at some point, but trim, badges, and hardware remain original, as does the seat. The engine casing covers and exhaust pipes look well-polished, and there are great details everywhere, such as the inverted fork, rear wheel guard, and dual-spring seat to name just a few.
The fully enclosed tandem sidecar is a Watsonian–founded in 1912, they remain one of the oldest manufacturers of sidecars still in existence. It’s an intriguing thing, with an unusual but attractive body shape, plenty of windows, a rollback canvas soft-top, a small luggage rack on the rear roof, and a decent-sized trunk in back.
Forest Green paint complements the gleaming black bike nicely, and the interior is fitted with handsome saddle colored weatherproof material. The tank wears an attractive, polished gauge pack, and Smiths instruments within still appear essentially as-new.
The 997cc eight valve four puts out 38 HP to the rear wheel, and should be capable of pushing the bike to speeds well over 100 MPH–at least without the sidecar attached. Torquey and smooth, the “Squariel” remain one of the most interesting British motorcycle engines ever built. Check out this great cutaway image for a clearer idea of its inner workings.
Described as completely sorted, the seller adds that the bike runs and rides well, adding: “No words might better describe the experience than these used in promotion of the Ariel Square Four, promising ‘Good performance and comfort with a genuinely refined feel.’”