Want to know the widest tire for my rim... Let me know what u guys think... Right now I'm running on 275's but would like to get 315's in the rear at some point but would I need to get a larger rim or can I stick with the 9.5 rim?

 

This is a picture of a 285/40/17 on my pickup... If you're going with a 45 series tire, a 315 may fit...
What I have found is that if the tire is too wide for the wheel, it allows the wheel to kind of swim in the tire because the sidewalls of the tire will flex and create a sloppy feel.
I had matching Yokohama 255/45/17s on an 8" wheel on the front of this truck and the truck didn't drive well and I couldn't figure out why so, I installed a 235/45 tire, which fit the rim nice and tight. No more slop...

 

I wouldn't run a 315 on a 9.5 wheel. I run a 285 on my 10" rear wheels and I've run a 295 on them in the past.

 

I have a 295 35 series on my 9.5" wheels and I would not run 1mm wider.

 

Yeah, that's about as wide as I would go too.