will 8" wheels fit, with 245/45/17?
 

Like title says. Not sure on the offset, but they're from a '99 Mustang GT. I have these on my RX-7, but my friend wants to borrow them for a vacation, since his tires are in dangerously bad condition, and mine are nearly brand new.

So, has anyone tried something that size?

Stock rim width for a mustang Gt from 99 to 04 is 8 inches
dont know the offset

Trust me I know stangs

Yes, I realize that, they're my wheels.

We went ahead and tried it. There is some minor rubbing on the front side of the plastic inner fender lining, and it rubbed once on the very inner most lip of the outer fender. I was quite surprised they fit in there as well as they did. Obviously, they stick out a bit more than the stock wheels, but that gives it a mean stance.

So you can swap out mustang wheels and mazda 3 wheels
if thats the case now i am REALLY pissed i sold my stock mach 1 rims

If you did swap the wheels, you'd probably be better off rolling the front fenders a tad. Either that, or going with a slightly skinnier tire than 245.

I have 19x8.5 on my car

Fender rolling should be a last option, unless you can get it done professionally where they guarantee the work. The problem with the procedure is that the paint becomes much more prone to cracking and developing corrosion. So if you do it yourself you're s**t outta luck if it happens .. but if you find wheels with the right offset you can bypass the whole thing. Just my $.02 on the topic ..