I agree with Scott about finding out the information, unfortunately sometimes it is innacurate. For instance the cross section width of the Hoosiers I have (mounted) is 9.74 inches. Hoosier (and therefore TireRack) specs say it is 9.3 inches wide. Perhaps unmounted it might be a little more narrow, but all of their 225 width tires are listed as 9.3 inches wide.
Anyway, regardless of that, if you go to a manufacturers website and search for overall tire height,or diameter, and cross section width, you can get a pretty good guideline by using the Hoosier specs I posted. I am quite certain that the Hoosier 225s are as wide as you would ever want to put on a GC8 chassis. They are, as I said, almost 235 widths in honesty. However, they are also shorter than stock size by a small amount. An average 205/55-16 is 24.9 inches in diameter. So the Hoosier is right at 4 tenths of an inch shorter than stock. Meanwhile a 225/45-17(again, average size) is 25.0 inches in diameter, which means it is a small amount taller than stock. What does all this mean?
Ok, from what I have seen in the adventures of making the Hoosiers (essentially a 235/45-16 tire) fit on my car, I would be willing to attempt a 225/45-17 if it is no more than 25 inches overall diameter. And you will definately need at least a 5mm spacer in the rear, I had to use a 1/4 inch spacer (6.35mm) and longer wheel studs. Plus, you are probably going to have to roll the front fenders.
To be honest, I don't know if I needed to do this in the rear, but I figured since I was at it I would go ahead. In my experience the rubbing problems on a GC8 occur against the strut in the rear, but against the top center inside fender lip in front during hard cornering or bumps. And somewhat against the top inside fender well during full lock steering (usually only low speed parking lot stuff). I have not had this problem with the Hoosiers since they are shorter than other wide tires I have fitted, even though they are wider. And to be completely honest with you about all of this I am only going to run the 225s for racing. On the street I will run 215/45-17s. I am just laying the info out for everyone.