It occurs to me that if a perfectly rigid wheel cannot roll, then it cannot do anything. The same practical arguments relating to molecular interactions etc. apply equally to its internal structure and make its existence impossible. As soon as we say "perfectly rigid wheel" we are in the realm of an idealised mathematical model. Any talk of atoms is absurd in this model, for many reasons. It's a bit like advancing practical reasons why a point particle, say, cannot move in a perfect circle.