I think your best bet is some kind of Nylon, purely for strenght and durability, its very strong and can withstand heavy impacts, it will flex (to an extent) then regain its shape!! question is what type?? im sure there would be many different types of 'mix'......
I could be wrong but if i was designing and molding, buggy/off road wheels it would be my first option!!
A bit of research is needed methinks!!!!
