What is that 3D printed wheel made of that it can support over half of your weight while bumping along a road?

ASA, per the post

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

Yes, but you could have made it out of PETG just the same. I have some PETG parts here that we have tried to break but couldn't, that stuff is ridiculously strong for its weight if you use the right infill and you take the layer direction into account when designing the part.