First of all make sure the wheels don’t hit the bus model by making a collisiongroup named i.e. “BusGroup” and all parts in the bus including the wheels should have this group. Then in the editor, make it so BusGroup parts cannot collide with one another.
Secondly, be sure all parts in the bus model except the wheels have the Massless property set to true. If needed you can add invisible weights later on.
Lastly I recommend using spheres instead of cylinders for the wheels, it’s best practice in cases like these. You can then make the spheres transparent and insert cylinders or even meshes as fake wheels by welding them to the sphere.
I thought of adding suspension with springs but it doesn’t seem like a viable solution. Perhaps change the physical properties of the wheels? Higher density and friction? Otherwise, I’m out of ideas.