Printing wheels

Is there a way to print wheels with a solid cylindrical hub in the center, and a different material for the flexible tire on the outside?

Yes, using a dual extruder setup you print an ABS core and a ninjaflex outer tire, you could either go with a solid wheel design, ora pneumatic one, which would require a bit more challenging design. If you look at the OpenRC project you should be able to see examples of wheels, tires, hubs, and even 3d printed shock struts.