A Swiss engineer known as Mr. Gerdes designed a monowheel. But these bikes weren't safe. So, their popularity was short-lived.
There is nothing on earth like a genuine, bona fide, electrified, six-foot monowheel. It's on our list of ideas from early 20th century gearheads that we wish had caught on, if only because they look so cool (definitely not because they’re safe).
The monowheel became something of a trend between world wars when exciting visions of the future seemed to spring from the joy that there even would be a future. Although dozens of varieties rolled out over the years since the 1860s, you're unlikely to see one. They now exist mostly in patent applications, magazine covers, and a handful of garages. Unsurprisingly, they’ve made plenty of appearances in sci-fi flicks, adding a measure of cool to otherwise mediocre movies.
The basic principle of the monowheel is easy to understand: Build a big enough wheel, and you can put a rider insider of it along with a motor to move the whole works forward. Early versions featured various combinations of motors (gas, electric, pedal-powered) and gear assemblies and are said to have reached speeds up to 93 mph–though their manufacturers were known to claim ludicrous speeds. Some versions were refined into relatively practical, not-totally-guaranteed-to-kill-you ways of getting around if you’re brave enough to hop in.
It was and remains a generally precarious mode of transportation. Besides the obvious degree of exposure and narrow point of balance, depending on the model (some featured little antennae-like balancing wheels, arguably rendering them non-mono) riders must learn to use their feet on the asphalt in order to counter the tilt of the wheel. If it’s not properly stabilized, or a driver is too fast and loose with the gas or brake, “garbling” is a real risk.