So you guys will have to forgive me I need help figuring out what tires I can use on my 15 with 17 inch rims. I know there's a lot of information out there that's a quick Google search or forum search away and I've seen it. The problem is I don't understand it so I need someone to break out the crayons.

Now what my plan is, I plan on putting a level in but whats the largest size tires can I use with out trouble? How do I understand the new numbers in relation to the ones on now-265 70 r17- how does it change my speedometer? Or would it be easier to bite the bullet and go up to 18s

The reason for all this is I'm putting a fairly decent set of all terrains on sense I got stuck in my stock tires

Figures I can do drug dose calculations in my head in the back of the ambulance but can't figure out tires
Thanks guys!

 

that might help making sense of the numbers:
http://www.rimsntires.com/specspro.jsp

plug in your stock size on one side, and play with the new tire size on the other. this will tell you how it affects your speedometer, how much larger in diameter the new tires are, etc...

as far as what fits and what not, there's a gigantic tire fitment thread here you might want to check

 

Why do you want a different size? The goodyear tires it comes with are horrible, they are more of highway tire. Upgrading to a good all terrain like BFG AT K02 in the standard 265/70R17 will keep you from getting stuck in snow or mud.

 

Honestly when it comes to the tire size its all looks because I don't have the mechanical know how to install a true lift or have the cash to shell out to pay a shop to do it. So i'm settling for a level kit and bigger tires