I just got rid of the factory 20s off of my truck and found a set of used toyo M55s for them in a 265/70/17. I thought about going bigger, but I also tow with my truck, so I didnt want to change to much to affect that. Check what your gear ratio is. I have the factory LSD and 3:92 gears in the rear end. If you have the 3:55s, you wont want to go too big of a tire or it will be a dog on the hills. I love the look of the steelies over the chrome 20s. I will try and get a pic posted of what my truck looks like with the new wheels and tires. A 315/70/17 is going to be a bit too big for our 2wd trucks....I think that with a leveling kit (2") they might fit, but they are almost 35s. the 4wd rams sit higher than the 2wds.