I owned an '05 Z before reverting back to the crossfire, to me, they are only a little faster (with a good driver maybe .5 of second faster thru the 1/4 and a deal heavier) The car did not have the character or the originality that the Crossfire has as they are a dime a dozen near me. Not to knock the car but through '05 (not sure of the '06's) they are plagued with front camber / tire feathering issues = you should have asked him if the new rims and tires were an attempt to deter this unfixable issue.