It will fit, but is not a good fit. I had some Kumho 275/40's put on my 17x8's at all four corners. It looked mean, but handled like crap. The rim is not wide enough, so the tire doesn't seat right. It also cupped a tiny bit in the middle. I tried all sorts of air pressures. It made the car dangerous as hell to drive. At the track is was so squirrly I never could give full throttle. On a stock car with 3.90 gears only. I put the 245/45's back on and noticed night and day driving difference. Even the guys at Discount Tire said I shouldn't put 275/40 on anything less than 9''. Les Schwab refused to do it, because their machine couldn't squeeze down the tire enough, and they claimed it was not smart to force the tire on the rim.
In short, 275/40 will fit on, but is not a good idea.