I modified lyshie's mBot hub so we could add some awesome tractor wheels to mbot.
The wheels are from an old (80's) John Deere tractor toy, which my son found in his grandma and grandpa's basement. I must have broken the original toy at least 30 years ago, but the wheels were still cool. :)
The hubs fit very tightly on mBot. Like, be careful pressing them on. But you may not needs screws once they're on.
The 1mm slot and lots of surface area hold the hub to the tractor wheel just fine for this application. Obviously a few drops of CA could make a permanent install for a more powerful vehicle. We're relying on friction for now. The inside of the hole that faces the tractor wheel is flat, but adding a square shaft could make things even tighter, but I didn't have time -- we needed to do a test drive before bedtime!
I used rafts and supports because it was hard to get the first, fairly precise layer to stick without, and there's a void that needs to be nice and flat underneath.
You're probably better at 3D printing than I am, so don't take my word for it...
Just mash it on the axle. Mine was very very tight. If you cant get it on the motor's axle, a teeny amount of filing with anything metal might help you out.