Been 10 years since I have measured for this, so I will do my best..

I used 15 X 8 with 245/60/15 tires ( rear) I spent a lot of time with a couple of used Mags with different backspacing measuring and looking at tire width and aspect dimensions... I did not want any tire rubbing or "nobody can ride in the back" crap sizing.. I still feel I installed the max you can go without any mods.. I had some rubbing on the inside of one fenderwell ( trunk side) and had to install a 1/8" wheel spacer.. Most of that problem went away with the FF rear sway bar that stopped most of the lean in the car..

The fender wells slope towards the tire/wheel ( both sides) so the area for your wheel and tire get smaller the higher you get up into the wheel well..
I remember thinking that I would have gone 5 1/8 BS if I was to do it again..
Just isn't a lot of room.

Hope this helps