Appropriate Wheel Offset for 18" Wheels?

Im not busting your balls here intentionally lol! Your mock up tire/wheel was a 275 tire yes, but on a 17x8. So your section measurements will not be over 10 wide I would bet. To end this debate here is what I would do: buy a pair of the fronts and mount the tires you want to run, then see what is needed in the rear with those. Prove me wrong!