the carpet at the nats was really bad in that it had a ton of ripples (i think cyrul's car actually got some air once) however i ran mine right at the limit and some guys i heard ran their's lower. however you want to smooth your chassis so it doesnt "catch" the carpet. rubbing is bad, however so is high CG, its a trade off between handling and scrubbing speed, if you are scrubbing too much speed so it defeats the purpose than dont do it.