Answers (1)
The concept of a hubless or centerless wheel goes back to the 1860s (a handpowered monowheel was patented by Richard Hemming in 1869) but it has not attracted much commercial interest until relatively recently due to material technology and safety/control issues. There is a centerless wheel monocycle which dates back to the 1930s developed by Govetosa and you can see a famous picture of one being ridden by an Indiana Jones lookalike online (check wikipedia on monocycles) and there are many others who have copied the same principle and applied it to everything from pushchairs to cars and of course there are modern varients around today almost all of which are of the monocycle type and only of a novelty value with little or no practical application.