Re: Tire size affecting mpg.???
Of course it will make a difference. Also if the tire is Low Rolling Resistance or not will effect it too.
The 2014 OEM 18" Tires are very good on MPG. I don't know too much about the 20's but I expect they are similar.
Not sure if Jeep used Low Rolling Resistance Tires in 2011. I don't think they did. The 2013 Dodge Dakota "Take-Off" Wheels I got had the same tire as the Jeep but were not the Low Rolling Resistance version. But they have a much higher wear rating.
01-15-2015 Overland 3.6L Black W/Black Int, Advanced Technology Group, Zeigler Lifetime MaxCare
Tires: OEM 20"/Nokian 18"
Situational awareness: Beltronics STi-R+