We made custom intake wheels this year using a casting process.
The original positive wheel model was 3D printed and then hot glued to a piece of foam board and then a ring from a 2L soda container was glued around it to create a mold frame. We then poured in Mold Star 16 fast from Smooth On into the mold frame creating a silicone negative mold.
To make the final pieces we used IE-3075 from Innovative polymers which is miles stronger than the Smooth-On products and is incredibly rigid. Looking back on it we should of used TP-4052 which has a higher impact strength but is slightly more flexible as we did have some issues with chipping on the thin side walls. We followed the
process detailed here for pouring the urethane. I made my own vacuum chamber from a old pressure cooker to degas the urethane.
The tread in the picture is urethane made by a local urethane company. They were able to cast a long tube of urethane in a size and color of our choosing. The company then cut the tube into strips on a lathe using an exacto knife as a cutting tool. It ended up costing us about 6$ per 1" wide tread. While treads can be cast at home the hot pouring processes that the manufacture uses creates a more durable tread for the equivalent durometer.