Time to Buy Tires for the Duster......help please.

Thanx for the reply Dartnut. I prefer not to mess with my freshly painted fender lips. How much clearance do you have on the inside of the rear tire to the springs?
I have about 1 1/2'' between the side of the tire and the leaf springs on both sides.
I could go 275 60 15s easily with the wheels offset at about 1'' more on the inside or 4 1/2'' backspace as some call it.
I tried factory 15 x 7'' rallyes on it and it was getting very close to the wheel lip.
The extra 1/2'' goes toward the wheel lip on the factory wheel, not towards the rear differential.
On a 15 x 7'' factory wheel, the offset to the inside is the same as on a factory 15 x 6 1/2'' wheel, which is 3 3/8''.
BTW, i tried the same tires and wheels on an A-Body 8 1/4'' rear that i had in the car originally, and the tires hit the springs even before tightening them down.