Adding backspacing by widening the wheel will do nothing to help/change your outer fender clearance.
Actually it should. I have a 255 mounted on it right now and have some minor rub issues on the drivers side. The car is already painted so I'd like to avoid more paint work or screwing up the paint that is already there.
Here's my thought. This 255 is tight to the front and is really maximum tire for an 8" rim. Widen the back half by 1/2" and it will move the tire back 1/4" from the front, giving me some clearance and a wider footprint from the wider wheel.
This makes sence in my head anyways. Anyone see fault to my logic?
I think I understand what you are trying to do... going to a wider rim will make the rubber sit with more of a /---\ shape instead of |---| This may help you.. but keep 2 things in mind:
1: Technically, you are changing the rim width to help resolve your problem...not the backspacing (although the backspacing will change in your case).
2: Personally, I think that tires looks best on the skinniest wheels possible. Wheel/tire packages where the wheel is too wide for the rubber look like ass. Not to mention that you want the rubber to be wider than the wheel and stick out past the wheel lip. You want this so that the rubber protects the wheel from contact with curbs, etc.
Have you rolled the fender lips yet? If not, spend the money doing this instead of messing with the wheels.