I wonder what wheels look like with a -4" backspacing. Are they going to stick out like a 1995 low rider?
as far as how much a wheel will "stick out" or "poke" takes in several measurements, to include backspace, which is a result of wheel width and offset.
Example:
A 6.5" wide wheel w/ -20mm (toward face of wheel) offset = 4" backspace.
A 8" wide wheel w/ 0 (zero) offset = 4" backspace.
A 9.5" wide wheel w/ +20mm offset = 4" backspace
edit: Each of the above wheels will poke differently despite having nearly the same backspace. Obviously, the wider (9.5") wheel will have the potential to poke the most as it has the widest width. I do not have all wheel specs memorized so I do not know for a fact the any of the above wheel configurations will poke as they were used to illustrate an example.
The more backspace one has, the further in (toward the car) the wheel will sit. Too much backspace and the wheel might hit the calipers or suspension depending on design.
The
tirerack explains offset and backspace. Check it out.