18' rims are a tad too big, OP. You turning it into a Monster Truck sort of thing? I think 2' is the absolute biggest you can go without doing quite a bit more to the car.
Also, you shouldn't threadjack, especially your own threads. It makes it very easy for you to end up with an unresolved problem. Also, I assure you, there are about 15 things on your car that need attending to more than large rims and headlight do-das. Just saying.
Not being a d!ck...just a Doug!