Triangle-wheeled bicycle - GIF

[mklotz]

The wheels are in the form of a Reuleaux triangle...

https://en.wikipedia.org/wiki/Reuleaux_triangle

a form that has a constant "width". (Use a caliper to measure the "diameter" and the value will be the same for any orientation of the caliper around the central axis of the triangle.) This means that they can be used in place of cylinders to serve as rollers supporting a flat plate placed across their high points.

The difference, of course, is that the height of the geometric center of the cylindrical roller above the ground remains constant while it rolls while that is not true for the RT. This fact accounts for the up/down motion of bicycle wheel attachment points. Good rollers, lousy wheels.

I made three RTs by gripping three lengths of equal-size hex in a 3jaw chuck, machining the exterior, rotating each piece in the chuck, machining, and repeating. As expected, they serve very well as rollers.