4wheels4life

I have 18x10 wheels now with a 13.5" wide tire on it and I am thinking of going to a 12.5". Will this rim still work when airing down? I wont have any problems with tires coming off of the beads as long as I don't go extremely low with pressure will I? I still think there will be enough tire bulge to protect the wheel lips with the 12.50's Or would it be cost effective to go to a 9" wide rim? If I do that I think I will go to a 17x9 rim as tires seem to be cheaper in the 17's compared to the 18's just hate to buy wheels and tires at the same time.