I melted plastic ones my first time at CMP.
I quit running them after that. All my Miata wheels require conical nuts, which are self-centering. I have had no eccentric wheel or loosening lug issues for the couple of years I've been running w/o them. I still check them prior to going out each session.
Personally, unless you have flat bottomed nuts, I don't see the need for hub-centric rings unless they're serving as spacers also. I will be running the widest permissable spacers on my E30. Those spacers are aluminum hub-centric. I believe the BMW wheels require conical nuts also.
Of course, now that I've posted my $.02 worth, Vincent will come charging in to crucify me.
