Maybe a front wheel/tire from a dirtbike would work well. The rim, axle, bearings etc. would be time proven to the task and assembly/removal would be cake. Also a larger diameter tire is beneficial in many ways. The "forks"-like structure that holds the wheel in place could run horizontal (parallel to the ground) and act as support for the frame.
Just keeping the ideas flowing.
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Gravity - It's not just a good idea, It's the law.
1998 Honda Valkyrie
1946 Chevy pickup