Calibrating speedometer - Difference between 225/75R16 and 255/75R17?
#1
JK Enthusiast
Thread Starter
Calibrating speedometer - Difference between 225/75R16 and 255/75R17?
My JK Sport (non-S model) came with the tiny 225/75R16 Goodyears. I'm about to put on a set of BFG Mud Terrain 255/75R17, which of course is the stock Rubicon set up. Here's my question: Do the folks at Jeep really do a different speedometer calibration between the two different stock tire sizes?
#5
JK Enthusiast
Thread Starter
#6
JK Super Freak
Good question, I did the same thing, Rubicon take-offs ; I "assumed" that there would be no re-flash necessary for the largest "stock" tires from the factory. Meaning, the computer would adjust for what is a factory size.
So I have to Flash for correct speedo, mpg readings ? Manual trans, so shift points not an issue as with auto.
So I have to Flash for correct speedo, mpg readings ? Manual trans, so shift points not an issue as with auto.
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#9
Factory would have outfitted the Jeep for that tire combo for sure = you will prob be off if you don't adjust.
Get the Flashcal, and make sure to do an actual measurement of the tire and enter that value - IIRC the stock Rubi setup comes in at 30.25" in the real world, but don't quote me on that one.
Confirm it with your phone or GPS after setting the flashcal, and you are good to go. Of note, I am pretty sure any changes to tire diam. in the tuner will override/reset any power level changes you make (again, this is from memory so I may be wrong on that - just recall reading it somewhere). Do some searches for both topics as the info is out there, in either case - the flachcal will be a nice mod for ya! (running a traildash here and like the 87 tune myself, runs better than mileage XS did and gets better fuel economy too!)
Get the Flashcal, and make sure to do an actual measurement of the tire and enter that value - IIRC the stock Rubi setup comes in at 30.25" in the real world, but don't quote me on that one.
Confirm it with your phone or GPS after setting the flashcal, and you are good to go. Of note, I am pretty sure any changes to tire diam. in the tuner will override/reset any power level changes you make (again, this is from memory so I may be wrong on that - just recall reading it somewhere). Do some searches for both topics as the info is out there, in either case - the flachcal will be a nice mod for ya! (running a traildash here and like the 87 tune myself, runs better than mileage XS did and gets better fuel economy too!)