new wheels and everthing changes

just bought some 18" alloys off ebay brand new set of 4 - £150 will wait and see when they come as they sound too good to be true. Did anyone see them on there? And what size tyres shall i go for, was thinking 225/45/18?

225/40/18 these have a overall circumfrence only 0.6% more then your regualr wheels