I'd be interested to know how well layers of 3d printing holds up to that much rotational mass, lateral forces, and vibration at freeway speeds. I have my doubts at this point of its feasibility.

A 3D printer could be used to create the mold for the rubber perhaps.

You can easily do a lost-wax process with a 3D printer.

(Although getting the precision may be difficult.)

Some folks have already moved on to a lost PLA casting process. I've seen some pretty decent results.

http://3dtopo.com/lostPLA/

NinjaFlex is a new type of material that some people are printing for rubber-like things, including little toy tires. Don't think it's ready for a car yet, but it's fun to play with.