the BS is measured from the outside edge of the lip to the back of the mounting flange, the width is measured from inside edge of the lip to inside edge. Most aluminum rims have roughly a 1/2" thick lip, so an 8.5" wheel will actually be 9.5" from the outside edge to outside edge of the wheel lip.
SO
if it's really an 8.5" rim, then it's going to measure 9.5" wide with a 4.75" centerline and a 3.75" BS, that means that you'll have 1" offset out (I prefer to use in and out rather than + and -, because what wheel manufacturers call + and - is reversed from what is used in a lot of chassis engineering books and it can be confusing). I do wonder if you really have an 8" rim, since that would be a more common size, and I'm also suprised that a 1" offset rim clears the fender lips well enough with a tire that wide.
That said, I'm asking you to confirm all these numbers since if you do you could be providing us the best data points WRT to what will fit that I've seen yet. I can calculate where the outside surface of your tire bulge is within about .1", and based on your picture I would guess that what most people would call a _perfect_ fit would be with that edge .25-.5" in from where you have them now (I think that most people would say that your tires stick out _a little_ but they more than close enough for 90% of people). Based on that and a little math I can calculate the offset or backspacing that you'd need to tuck just about any tire in that can possibly fit in the wheel well (well, with a little bit of allowance for height, but since your 245's are around 26.5" tall, taller than most normal tires you've even accounted for that).
BTW, usually at least the rim width is cast into the back of the rim (the offset is usually not because the final setting is determined by machining)
BTW2, depending on the hub thickness and they type of lug seats, if you're ambitious you might be able to machine the hubs down enough to get the rims to tuck at least another .25" in, maybe more. Typically if they're machined for washer seat lugs and have a thick hub you can make a lot of change without weakening the rim, tapered seat lugs not so much so.
xoliex- again, I'd like to see pics of your car and any more details you can give, that should confirm my math and his numbers.
I don't know if this will help you, but I'm running 15x8 American racing 200s on the rear with a 4.75 backspacing and I do have to use air shocks to keep the body off the sidewalls.
The wheels your considering do look really sweet! I've always liked the look of the "Slots"! ::thumb::
QCode... I found these pics of your car (I love daisy mags, beautiful car, sweet stance):
What size are those back tires? Do the outer fender lips tend to touch or are you hitting on the inside somewhere without the air shocks?
What's your front tire and wheel size/offset???
This one would also be very helpful in figuring this out, especially since you seem to have a very nice fit with a great stance and largish tires.
I'll try to pull the rims that came on mine off also and do some measuring (I think they're a set of old school centerline Champ 500's, but they're missing caps...), but they're not really big enough to get really good numbers off of (I think they're 15x7 with 235 60 15's on all 4, they look just slightly better stance wise than a set of stockers. Honestly, I'd probably be OK with them if I could find a matching set of 15x10 or at least 15x8.5 for the back, they have just enough old school cool for me to deal with them. Not as nice as a set of Daisies or Jellybeans... interestingly my tires are seriously rotted but hold air fine... I guess that's par for the course for this car.