you need to transfer over your TPS(tire pressure sensors) which are apart of the valve stems
Either that or if the 18's have sensors in them currently then they need to be programed to the car which might have to go to the dealer;.
it'll just get annoying after a while. and i've heard rumors of it retarding performance in certain conditions. i've never seen it but i don't have the sensors in my car to test it out.