Great info AJ thank you. At this piont I am considering doing a us car tool spring relocation kit to run a 15x8 in the back. Otherwise I think your call of 225/60 all the way around would be a wise choice.
You don't need a 3" relocation to run a 15x8. You can run a 15x8 with the stock spring locations, and probably use a 245 on most cars, but you need a 15x8 with the correct backspacing. Doing a spring offset doesn't change that, in fact, it puts all the extra space on the
inside of the wheel well. Which means, you need to run MORE backspacing to take advantage of it.
As I said earlier, a 245/60/15 with a zero offset rim is marginal. It has been done by guys running the SBP 8 3/4, but not everyone has success. If you're willing to do some work on the quarter lips, you can probably make it work. Zero offset on a 15x8 would be a 4.5" backspace. Ideally, you'd want a 15x8 with a +6 offset, which is a 4.75" backspace for an 8" rim (or 4.25" for a 7" wide rim). Unfortunately, in 15x8" rims the 0 offset is usually about the best you can do in a lot of styles, at least off the shelf. Even the +6 offset or 4.75" backspace usually takes a custom order.
Also, if you're not planning on doing a mini-tub, there's no reason to do the 3" relocation. You can use a 1/2" spring hanger/shackle offset and get the same amount of room, because at that point the inner wheel tub will be the limiting factor. The 1/2" offset kit is a bolt in deal on the chassis, obviously you do need to move the spring perches on the axle in.
So would 235/60 on 14x7 cragars not work on my 68 dart or would that be pushing it?
14x7" with a 4" backspace and SBP right?
The 235's should work in the back. In the front, it will be tight. By the math, if that combo were on a BBP front end it would stick out about .27" past the 275/35/18's on my car. Now, the change from SBP to BBP is more than that in offset, so, they should work. But, my fenders aren't in the stock location anymore. I pulled them a little when I installed them, and I've since rolled the lips and pushed them out further. Now, my car sits low, and that's most of why I did that. So, in the front I think it will work, but it will be close, and the lower your car is the more potential for rubbing you'll have.