What size of tires does my 1998 Nissan Altima need if i got 18in rims?

The rims are Motegi Racing wheels with a 40 offset and 4 lug 18in.. i went to discount tire and they said 215/40/18 or 205/40/18? is this correct.|||Both will work, but a 215/40/18 will be closer to your stock wheel/tire diameter and thus will give you a more accurate speedometer reading.