wheels/tires please help

[WVUFAN18]

I have no help from my local tire dealerships so I really need to rely on those of you with much more experience then me.  Like everyone I want bigger tires.  I am also changing wheels; going with 18x9.  My question:  what is the widest tire I can go with on a 18x9 with 5.0BS or 5.5BS?  I initially wanted to go with 5.5 to keep the tire under the fender as much as possible but I'm worried that a wider tire will have clearance issues.  I have a 2011 Rubicon.  Any suggestions / thoughts / ideas will be greatly appreciated.  I am going crazy trying to figure this @%$# out!

[CJ8Ted]

Tires should not go over two inches over the rim width. That being said I run a 12.5 tire on a 8 inch rim its only a half inch but it is over what is recommend. As for the back space on a JK, sorry IDK about the new stuff.

Ted