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What exactly will reprogramming the speedo do?

blkhawk_jl

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I know entering the right tire size will adjust the Speedo to show your correct speed and economy, but does it do anything else besides that? I’ve heard it’ll change the transmission shift points based on the tire size. Will doing this be a better bet than a full blown regear? Currently running 34” bfg k02 from the stock 31” all terrains
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Spdu4ia

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would like to know as well as i have 35s on my sport and havn't done the re calibration yet
 

Paluss

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It doesn’t do anything else but what’s mentioned quoted.
I know entering the right tire size will adjust the Speedo to show your correct speed and economy, but does it do anything else besides that? I’ve heard it’ll change the transmission shift points based on the tire size. Will doing this be a better bet than a full blown regear? Currently running 34” bfg k02 from the stock 31” all terrains
I upgraded my Rubicon to 35" KO2 and had the dealer do the speedo software upgrade. Yes, the speedo will now reflect the correct MPH, and all of the mpg calculations will be adjusted too, eventually the transmission shift points learn the new accelerator inputs (I noticed it after 100 miles on a long drive).

A re-gear is not necessary for the JLUR only on non JLURs with upgrades of 35 and larger is what I am told...
 

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blkhawk_jl

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I upgraded my Rubicon to 35" KO2 and had the dealer do the speedo software upgrade. Yes, the speedo will now reflect the correct MPH, and all of the mpg calculations will be adjusted too, eventually the transmission shift points learn the new accelerator inputs (I noticed it after 100 miles on a long drive).

A re-gear is not necessary for the JLUR only on non JLURs with upgrades of 35 and larger is what I am told...
Thanks!
 

nerubi

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They just had this on Motor Week. Changing tire/wheel size to a different ratio than stock may also impact safety systems related to wheel sensors.
 

Uhdinator

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Odometer will not be accurate, ABS, and traction control likely effected. The transmission is adaptive. Slam the skinny pedal all the time and the shift points move up to higher rpm's. Drive like a granny and they move to lower rpm's. Pull the Trans cont module (TCM) fuse to reset it.
 

Stickman3

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would like to know as well as i have 35s on my sport and havn't done the re calibration yet
I just tuned my JL for 35 in tires, My speedometer was almost 10 miles off and it showed better gas mileage then actual....You have to change the gear ratio as well when you change tire size.. I looked up and found that a ratio of 4.25 would give a better shift /rpm and hopefully better mileage.... But changing just tire size does not change the shift points.....
 

swflfireguy

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I just went from 32" tires to 33" tires. I thought it was no big deal, but before installing the Tazer, the trans wouldn't shift into 8th gear on the highway, I had to do it manually. After re-programming, it shifts as it should and the MPG is correct. Prior to the programmer, the speedo was off about 3 MPH 73- reading vs. 70 actual.
 

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jeepingib

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I just tuned my JL for 35 in tires, My speedometer was almost 10 miles off and it showed better gas mileage then actual....You have to change the gear ratio as well when you change tire size.. I looked up and found that a ratio of 4.25 would give a better shift /rpm and hopefully better mileage.... But changing just tire size does not change the shift points.....
So this is where things went wrong for your situation. You should have continued to adjust tire size to reflect speed correctly. Most tire manufacturers do not produce tires that are true to size. So even though you put 35 into your Tazer, it won't read correctly, because the tire is not actually 35 + errors in how the computer reads sizes. Best advice I can give you is to set your gear ratio back to the stock setting, and adjust your tire size until the speed reads accurately by GPS. The faster you are going when fine tuning your adjustment, the more accurate it will be.
 

WranglerMan

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I ran with a Tazer for along time and used it to correct my tire size among other things and I rarely saw 8th gear as the additional rolling mass of the wheels and tires along with the steel bumper and winch affected it and now I don’t have a Tazer anymore and the only difference is my speedo is off along with average MPG
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