The 2004 record still stands in the category of 'fastest monowheel'
A man shows off the Mini Mono Wheel during a press preview 
at a motor show in Essen, Germany. The machine can reach 86.5 km/hr
[53.7 mph], a world record for that type of vehicle. (Photo: Michael Sohn/AP - link)
Apparently, the monowheel design dates back to pre-industrial times with many variations developed on the theme and designs resembling at various times a bicycle, a hamster wheel, a gyroscope, a horse-drawn carriage and a giant tractor tire.
While the unicycle as we know it today was - like the bicycle - still in its Penny farthing infancy, a strange looking propellered version of the monowheel made the cover of Popular Mechanics back in April 1914 with the name, 'unicycle' and later, in response to a request for funding, 'a mechanical freak'. Motorized versions continued to develop through the 20s, but advances in monowheels stalled in the mid-30s, presumably left in the dust of the automobile.
Kerry McLean is the guy who's up to making them go fast nowadays and also, more comfortable. Aiming for comfort over record speeds, here's a larger version of a monowheel- the 'monocycle' :