I found the perfect offset/wheel width was et35 7.5j, this is just on the limits of 'about to hit arch', so won't scrub, but only just. So, if the wheels you have are et43 (i think) and 6.5j (again i think), then in theory you need 20mm spacers front and rear to bring them to this point (8mm would bring it out to et35, then 12mm would bring it out to the equivilant of 7.5j)
As per sig pic, and this
and this,
ok, so those were 16's, but they would poke out the same.