We have found that we can stuff 15 x 10 on 4.5" backspace into our '86 - '88 Olds 442 G bodies without ANY rubbing! Rims in use are the Wheel Vintiques Olds Rallye Repro SSII Type and the tire sizes used are 245 60 15's, with 26.5" height, 9.64" section width, and 5.78" sidewall.
Here is a great resource for translating the tire sizes:
http://www.americanracing.com/techce...Calculator.htm
With this resource, you should be able to nail down your 18's just right. The Extreme Plus 14" Baer 6 Piston system we will be installing sometime soon had me recalc for 18's, and I came up with 245 45 18, which provides a 26.6" height, 9.64" section width, and 4.34" sidewall.
If you want to see what this looks like in motion, we have action vids on our 'site - check 'em out and see what you think about the look with these size wheels / tires.
http://www.hydratechbraking.com/mult...os/movie_5.WMV
http://www.hydratechbraking.com/mult...os/movie_6.WMV
