factory bullitt rim is 18x8.5 with a 50mm offset.You could run 255/45/18's and the overall diameter is the same as the 235/50/18's.The 245/55/18 is just a bit wider but fits really good.
You could deep dish Bullitts 18x9's-255/45/18's up front(36)45mm offset) and 18x10's-275/45-295/45's(40 to 45mm offset) out back for wider tires and rims.
Here is a list of different tire sizes.S-197 over diameter is 27" and if you keep the tire height the same your speedo won't be affected. http://www.bfgoodrichtires.com/specs/g-force-t-a-kdw/22.html
you can go 275/45/18 on the rear, they are approved for a 8.5" rim, they are pricey tho. I have 265/40/18 MT DRs on my rear, a bit shorter then stock but fit fine, been using that size for near 2 yrs now.
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