If you read the sticky at the beginning of the discussion page, you should find your answer, and some other alternatives. Usable tire width is determined by a lot of factors.
Best to choose a set of wheels or at least choose a certain rim diameter before talking tires. Depending on the rim's backspacing available will depend on how much tire you can stuff in there.
I put a just the rim off a 86 or 87 mustang that was 15 x 7 rim and there seemed to be plenty of room????? It wasn't rubbing on anything when I turned it.
Have you actually driven it with those wheels on it? I put '88 GT wheels on mine, and it seemed great - in the air. As soon as I put the car on the ground, the inside lip of the rim hit the control arm solidly. I'm running 1/4" spacers, and I ground the inside lip of the rim a bit too. I've got 225/60R15 tires on it.
The car just has one coat of primer on it as it was just stripped down to bear metal just days ago. I took off the white and blues stripes to make it black with the gold stripes. I think it looks much better.
