correct me if im wrong but doesnt a 30 series 19" rim have the same rolling diameter as a 45 series 18" rim....? Sorry, No idea mate.. I just read about people losing power and 1/4 mile times with bigger wheels and I've seen it on dyno's. And..I'm just a bit peeved at all these blokes ringing me looking to buy my T and saying stuff like, "the last one I looked at had big wheels on it, boo hoo". I've been telling them that I'm waiting for a buyer who wants a quick car and that they should go buy their big wheels. lol..