You probably could, but I don't think its recommended... 315 = over 12" I think the recommended is 265 with a max of 275?
You can, but it'd be stupid. I have 275s on my 9.5s. I wouldn't run anything wider. I'm actually going to go to 265s when it's time for new tires.
Eh, I think a 285 would be fine for a 9.5", since most people run a 275 on a 9" but a 315 would just bulge way too much
I put some 315's on my old 9" wide wheels and I had to use ether to get the bead seated. They were so wide compared to the rim that it was making the tire bunch up when we tried to mount it. The 275's I had on there fit perfect. The sidewall is straight up and down and looked to be the exact same width as the rim.
Different tires will be different widths but be labeled the same size. I had a 275 Nitto NT01 and Toyo R888 on a 18x9.5, they both had bulge. I consider it bulge because I like straight up and down on the race car.