We keep getting asked if our HD springs will stop my wheels rubbing and the answer is no !
As long as the wheels are the correct dimensions then you can take the rear springs clean out and still drive on the bumpstops with NO SPRINGS !
If you are looking at wheels which have a lower offset (ET/Backspacing) of 42mm i.e 35mm then you are going to get problems as the lower the figure the more they will protrude past the wheelarch which is trouble.
If your wheels are rubbing then you need new wheels or possibly new tyres (we only use a 225/45/18 tyre on our T4's) springs no matter how strong are meant to compress and will do so if you hit a bump fast enough !
Meanwhile here is a a pic of one of my spanking hot Rondells with an offset of 13mm and 8.5" wide which if you paid attention in class above won't work on a T4 !
Peace !