Crc rims are nylon and indestructible. Shumi/pit premount are abs rims and come pre-cracked in the package. If not they will soon crack on the track. Not sure about gravity. I know they were using abs in their USGT rims and they crack. I think abs belongs on static models but that's my opinion. I asked Paul about the USGT rims and he prefers abs as he feels they run truer. I don't doubt this at all as I know the crc premounts are a bit wobbly. All the gravitys I've ever ran were nice and true. Really personal preference. Not sure what the plastic composition of the sweeps are.