I used to have 235/60x15 on a 8" wheel with 4.75 ackspace, and had no rubbing anywhere with plenty of room.
I've recently switched to a 255/50x15 on a 8" rim with 4.5" back space. While everything fits, it is very close and body roll will deterimine interference. I'm thinking I may need to roll the fender lip to avoid cutting the tires. That difference in .25" spacing may be the difference.
