tire size?
 

im puting a 3" leveling kit on a 05 cummins with stock rims what size tires can i run with out rubing

I am running 35's with my leveling kit and I rub just slightly at full lock. That being said, I will never buy 35's for my truck again. I am really noticing the lack of power going from a 265. I think I will compromise with a 305 or 285 next time.

315's will be almost 35 inch tires and like 12in wide or so

Tire?
 

I'm running 35" Nitto Trail Grapplers w/ 2" leveln, only slight rub at full lock. I've had these tires on for 11,000 miles and they are barely showing any signs of wear, I will def. get them again. Quiter then MT/Rs and BFGs that Ive run before.

Yup, I believe 315/70 R17s are ABOUT a 35 x 12.5. You will definitely not have clearance issues. If you are using stock wheels you may rub on you lower control arm a little bit when you cut the wheel all the way.