Just doing some research, good info here...for my own info.
http://features.evolutionm.net/article/evomfeatures/46
"The common shave for a full race set-up is at least 4/32. For Track day events we recommend at least 6/32 shave. If you plan on using them for everyday summer driving, then leave them full skid. It is important to leave the tires with as much tread as possible for street driving in case of rain."