wheel well size Duster

~12" from the inside of the stock wheel well to the inner edge of the lip at the top of the wheel opening. But the lip on the wheel arch is a good 5/8" wide, so you could get some more space there.

Still, I would think that 295's would be the absolute widest you could go, and that would probably include trimming the lip on the wheel arch and getting the backspace perfect. And then you'd still be limited on how much you could lower the car before they started rubbing. And that would be after a spring offset.

I had a set of 275/40/17's on the back of my Duster with the stock rear and springs, 17x9's with a 5" backspace. I needed a 1/4" spacer to get the tires off the spring, but I got almost the entire 1/4" in clearance (the tires just barely touched without it). Top of the wheel arch was right at the top of the tires, I'd guess that I would have had to do some trimming to keep them from rubbing if the back of the car was any lower.