Today, monowheels are still around, though they aren't being floated as practical replacements for cars anymore. Many are built by hobbyists and amateur engineers and most are used for entertainment purposes.
Builder Kerry McLean created a monowheel powered by a Buick V-8 engine that's capable of more than 50 miles per hour (80.5 kilometers per hour). Amazingly, his creation is street-legal in all 50 states (but good luck explaining it to the police if you get pulled over for speeding.) McLean calls his monowheel the Rocket Roadster, and despite suffering a bad wipeout in one, McLean continues to build his unique vehicles to this day.
Another fun design comes from Jake Lyall, who created a contraption called the RIOT Wheel. This vehicle features an engine inside a huge tire, and the driver sits in a seat outside the wheel where he steers. When the RIOT Wheel is in motion, it keeps the seat upright and in the air. While Lyall built the monowheel for the Burning Man festival, he's working on other single-wheel projects, and is attempting to conquer the land speed record [source: The RIOT Wheel].
Despite its long history, the first commercially available monowheel went on sale in 2007. The Netherlands-built Wheelsurf is powered by a tiny, 31cc Honda four-stroke engine, and it's capable of speeds up to 25 miles per hour (40.2 kilometers per hour). The Wheelsurf is extremely lightweight and it's steered by the driver shifting his or her weight from side to side. Unfortunately, the company says it's not street-legal in most countries -- but it is a lot of fun to be had for $7,000 [source: Wheelsurf].
So as you can see, designers still like to play around with monowheel concepts. One designer, Shaun Stevens, has even showed off his idea for an electrically-powered monowheel-motorcycle hybrid. The design is dubbed the Audi AM [source: EcoFriend]. And while the stylish one-wheeler will likely never see production, it, along with many other modern examples of monowheel design, shows that intrepid designers and engineers haven't given up on monowheels yet.
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