Another quick thought last night as I was trying to sleep…
But wouldn’t a torus work as a pretty decent primitive collision shape? It is basically a capsule but instead of defining a volume based on line length along another line, it would be based on line length from a circle.
It would be more expensive than a sphere, but would it be much more expensive than a capsule? Anyway it would make a perfect collider for thinner wheels, since it’s a perfect bike tube shape to begin with.
