3" rear drop, what tires will fit???

OK, so I'm dropping my truck 3" in the rear and I want to keep on 15 inch rims. How wide can I go and how high can I go. This is my first mazda and don't know a whole lot of what I can put on it.
Can I put on a 30 x 12 tire without it rubbing???? I don't want to do any cutting but I can bang out the inner lip if need be.