I spoke with some guys at a
conference yesterday and had the pleasure of discussing robotics design with a guy from American Plastics Manufacturing based out of southern IN. They specialize in injection molding. There are a few rules of thumb he described and this particular wheel appears to break two of them: Keep a UNIFORM wall thickness, and have NO sharp corners.
Injection molded plastic has a flow direction, and all polymer compounds shrink 0.5%-3.0% depending on the compound. Most likely you'd go with a crystalline-type plastic material for the wheels, which also has unpredictable shrinkage. This shrinkage causes a variable wall thickness injection to shrink at different
rates, thereby warping whatever item you're trying to make. When the variance is too great, many times the thicker area of the part will crack since the plastic is still trying to shrink after cooling down. In addition, a sharp corner will not have plastic flow smoothly through it, which will cause a non-uniform shrinkage at the corner when it cools. This severely weakens the corner.
He had some equations up, and depending on the strength of the plastic material you choose for the wheel I'd estimate that you'd want a solid 1/4" thickness all the way around, with (and this is critical) no lower than a 1/2" radius on the fillets. If you use a non-crystalline plastic, then you can have a slight variance for your thicknesses, but not much. AM's wheels are ingeniusly designed and have the right material composition. Though as a warning, since polycarb is non-crystalline, I now think that teams should take the weight of the bot off the wheels while it's in shipment, since the shipments can go through various extremes of heat which will cause the polycarb to creep.
Hope this helps if you still decide to do molding. -- edit -- As a followup, if you do want to do the molding, follow the link above to the conference and get the contact info of the APM guy. He was glad to give me a couple of pointers, and probably wouldn't mind spending a few minutes looking at your design.