i found a cool youtube channel when pondering about ducting. i can see this being an easy way to create ducting similar to the hard motorsport 3d printed pieces.... use regular ducting, then flatten it out where it would make contact with the tire.
this stuff is cheap enough to have some fun experimenting with!
link to the casting material;
https://www.amazon.com/gp/product/B0...KZ44CJMXVBT2FS