Tires and wheel question.

I've been playing around on this site:

http://www.rims-n-tires.com/rt_specs.jsp

You just put in the info for what you currently have that you know will fit your car on the left side & then try out whatever combo of wheel & tire you want on the right.

It pretty much seems to throw all of my figuring out the window. If I can believe it, it looks like a Centerline 15 x 8.5" wheel with a 4.875" backspace (+3mm offset) will work to put a 265/50 15 (Mastercraft makes one) tire in the back with offset springs, MAYBE a 275/50 15. You might even be able to get away with the 265/50 tire without offset springs. If you use this site, don't just rely on the dimensions that the site puts in for the tires. Double check them with the tire manufacturer's info. The tires seem to usually be a bit wider than the calculator says.