1970 dart max wheel size

Well, if my ‘71 Dart is any indication then a 15x8 with 4.5” of backspace paired with an A-body 8 3/4 with BBP axles won’t be enough backspace to max out your tire size.

On my car the wheel mounting surface to the stock spring location is 6”, but it’s only 5” to to the quarter. To center the rim, which you’ll have to do if you want to max out the tire size, you’ll need a 1/2” of offset (13mm, since offset is always measured in mm). So your 15x8’s would need a +13 offset, or a 5” backspace.

But you should definitely measure your car before you start spending money. Some have less room than others, and some are even different from one side to the other.