I just put 315 70 17 kelly safari on my 4dr rubicon 2008 auto. when I first did it i had not re-flashed for the bigger tire. Sure it may my mileage look like crap at about 8 mpg. but it wasn't bad at all. kinda erie to be have the speedo say 60 and be blowing by everything on the freeway. and far from the go I was expecting it seems pretty good around town and up and down steep local hills. Encinitas CA Next I re-flashed it to the tire size so my mileage jumps up so to speak to about 14 mixed city and freeway. but it seems al little doggier barely just barely..
so when the motor was turning the bigger tires at the old calibration it would be shifting at what perceived was the correct speed and Higher rpm? but was actually faster due to the larger tires correct?

or is the opposite way?

can this be used to an advantage in performance even thought speedo would be off?