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Discussion Starter #1
Wife and I purchased our 2016 Jeep JKU in February and immediately switched from the stock 16" steel wheels to stock 17" alloys. We have 3.21 gears as this is her daily driver since she works closer to home. The question I have, is the Jeep programmed from the factory to accommodate the 16" wheels and 225 tires? Our average MPG since ownership has been 15-16mpg with the 17" alloys and Wrangler SRA tires. Her drive to work is about 23 miles open roads, light traffic and 70mph limit. Just trying to see if maybe a Procal or other programmer would help with the difference in tire size? BTW, we have almost 3,000 miles on the Jeep. Thanks in advance for any and all help!

Collin C.
 

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Jeeps are programmed from the factory for their tire size, you moved from a 225/75/16 (29”x9”) to a 255/75/17 (32”x10”) so the computer needs to be told the tire size changed.

Hope that helps :thumb:


EDIT: Superchips flashcal or AEV procal seem to be the favorites, both my Jeeps have the superchips.
 

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And since you changed to another stock tire size, a dealer can make the change for you. If you intend to stay with this stock tire size for a long time, and have no other use for a Procal or similar device, it may be better to have the dealer make the change.
 

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I went from the 16" steelies clear up to 315 Duratracs. If I remember correctly, the speedometer was about 5mph low at highway speed (reading 55 @60mph). My wild ass guess would be that you're about 3mph off at that speed. Since everything is calculated off this, your reported mileage is slightly incorrect too.

I adjusted mine with a Procal, might not even be worth worrying about going from the 29's to 32's.
 

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dealership should charge no more than 1/2hr labour to make the update to your computer. if they've done this before they can do it in 10-15 mins!
 

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Discussion Starter #6
I went from the 16" steelies clear up to 315 Duratracs. If I remember correctly, the speedometer was about 5mph low at highway speed (reading 55 @60mph). My wild ass guess would be that you're about 3mph off at that speed. Since everything is calculated off this, your reported mileage is slightly incorrect too.

I adjusted mine with a Procal, might not even be worth worrying about going from the 29's to 32's.
Our speedometer is off by 5mph. Shows 65mph but gps reads 70mph (verified the gps reading in our 2015 civic and it was dead on) also the gas mileage is calculated by me not going by the evic. I'll call the dealer Monday to see what they'll charge but we may buy a Procal since we're considering larger tires in the future.
 

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Speedometer and odometer inaccuracies are not the only concern, especially if you have an automatic transmission. The computer needs to know the correct axle ratio and tire size for accurate calculations about road speed and torque demands/estimates at different points throughout the drivetrain. The automatic transmission may exhibit some less than ideal shifting behavior of these are not calibrated properly.
 

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Our speedometer is off by 5mph. Shows 65mph but gps reads 70mph (verified the gps reading in our 2015 civic and it was dead on) also the gas mileage is calculated by me not going by the evic. I'll call the dealer Monday to see what they'll charge but we may buy a Procal since we're considering larger tires in the future.
Your calculation will be off, because the speedometer thinks you are going slower than you really are. That translates to the odometer as well, so what you think is say, 300 miles, the reality is that you went maybe 270 miles. Your MPG would be adversely affected, and would be lower than it actually is.
 

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Discussion Starter #9
****Update****

One year after starting this thread I finally got an AEV Procal. We went from the 16" steelies, 17" with 255 and now 17"x9" with 285/70/17 tires. Set the Procal to 32.25" tire height and took it for a spin. Immediately noticed a huge difference in the Jeep. Shifts smoother, speedo is dead on now and just way more responsive. Only regret I have is not getting the Procal sooner.
 
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