Stock offset is 55mm. Something around 50mm to 45mm should work fine.
I have 15 x 7 race wheels with +45mm offset. I run 225/50/15 on the track, and I don't have any rubbing problems. The tires rubbed on that little inner piece of the rear bumper, but you can't see it, so you can trim the piece off.
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Billy
North Texas Prelude Owners Group
www.ntpog.org