Andy I have thought about displacing some material with cheeper means on the inside of tire. That may be a bit more advanced than I've got yet. That would really require a three part mold. As the mold part on the inside of tire would have to be secured/suspended during casting and then on removal from mold a three part would be better (I think)
. And they may be a little bit more casting material but it will also end up more added weight. I would imagine each tire will be weighing around 2-3 pounds. Just a uneducated guess right now. I'm not even sure the casting resin I am getting is the right hardness. Won't really know till I make one
. I'm shooting for a shore hardness of 60 that should be like a sneaker bottom. Softer than a super gummy tire.