With 18's your looking at 225/40/18 tires. Personally the "40" is why I didn't go with the 18's. Like I said earlier, I bent a few rims already.
Try places like
www.tirerack.com they give a lot of info on the rims they sell and
www.1010tires.com has a very handy tire size calulator to make sure the speedo stays right on the money.
Also "Kwhauck" posted this the other day
http://www.aleromod.com/forums/showthread.php?t=16193
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33% ALEROMOD OWNER!!
2000 Olds Alero 3400 SFI 14.53 @ 94.93
1985 Olds Delta 88 307 SBO 17.96 @ 76.99
2007 Volvo V50 T5 6M 15.782 @ 89.12
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