Speedo change?

Moose340 · **Joined:** Tue May 03, 2011 11:38 pm **Posts:** 505

Hey guys and gals, I was wondering where to get a sensor or gear thatll change my speedo when I get bigger tires on it. A point in the right direction woul dhelp greatly.
Thanks

RED_KJ_666 · **Posted:** Mon Aug 08, 2011 5:59 pm

It's all electronic, You'll have to go to the dealership and have it re calibrated.

Offroad_RN · **Posted:** Mon Aug 08, 2011 6:20 pm

Hello, I assume you have a jeep liberty correct ?

Their is no gear or sensor that will make that correction. The speedometer is tied in with the PCM = powertrain control module ....a.k.a the liberty's computer. Apparently their is a way the dealer can make those changes and plug in the tire ratio and or a different gear ratio. Most dealers may have the necessary equipment but do not know how to do it !! If memory serves me correct from some older post this computer change may not be possible in the newer jeep liberty's PCM ?

I would also like to have this correction done when I get a taller tire, maybe someone who has done it can chime in on the subject.

Dont mean to anwser a question with a question but I wonder if the people who do the B&G flash can make these changes ?

RED_KJ_666 · **Posted:** Mon Aug 08, 2011 6:40 pm

Unsure on the B&M flash question, but the Liberty's computer only has a set number of tire sizes it can work with outside of that you can input the Revolutions per mile of the tire to achieve the same goal while re-gearing.

Moose340 · **Joined:** Tue May 03, 2011 11:38 pm **Posts:** 505

Well Id like to have it changed so Ill have to check into it

ATXKJ · **Posted:** Mon Aug 08, 2011 7:18 pm

it's called a pinion reset - and the dealers here can't figure out how to do it.....

RED_KJ_666 · **Posted:** Mon Aug 08, 2011 10:56 pm

Yeah one dealer in town flat out said that it couldn't be done, at the other the service counter guy gave me a weird look and started saying they couldn't do that when the shop foreman walked by and called him a idiot and explained to him that it was pretty simple and he could do it.

Ryn7 · **Posted:** Wed Aug 10, 2011 6:34 am

It's called a Pinion reset.
The local Chrysler dealership did it for free for our Rig.
Took the mechanic all of five minutes to do it once I gave
him the Revolutions per mile/Kilometer.

Offroad_RN · **Posted:** Wed Aug 10, 2011 12:20 pm

Maybe someone who has had it done can get some directions on what menu's to use on the drb3 scan tool. Anybody do it with a gear change ? or do u have to bust out a calculator and try and figure it out ?

Moose340 · **Joined:** Tue May 03, 2011 11:38 pm **Posts:** 505

http://www.discounttire.com/dtcs/infoTireMath.dos
Heres a cool little do-hicky that I found to help

Ryn7 · **Posted:** Wed Aug 10, 2011 10:30 pm

Here's another good tire calculator.
http://www.csgnetwork.com/tireinfo4calc.html

black and blue · **Posted:** Fri Dec 30, 2011 4:16 pm

Just went to do mine.

The tech didnt know how to do it by changing the RPM. He said all he could do is input the biggest tire size possible.

For my '09, he said the largest tire he could do was 245/50R20 (29.6" Dia/680 RPM)

My new tires are 255/70R17. The standard RPM for this size tire is 649, but Nitto says the RPM for their terra grapplers in this size is 669

does anyone know the reason for this discrepancy? I could see the RPM being slightly different b/w different manufacturers, but off by 20 RPM? 669 computes to a 30.14" tire while my tires are spec'd to 31.06"

i told the tech I was worried about the auto tranny, but he said the speedometer being off wouldnt affect it b/c the computer relearns how to respond with the bigger tires installed

honestly i dont understand how the speedometer would affect the transmission... i always figured shift changes are based on the tach, not the speed...

bunkermonkeycw · **Posted:** Fri Dec 30, 2011 4:44 pm

I tried to have mine fixed and they told me there were just a few select tire sizes to choose from, stock and smaller stock... Interested in an 06s experience.

teckman02 · **Posted:** Fri Dec 30, 2011 4:50 pm

has anyone thought about getting this.

http://www.superlift.com/accessories/truspeed.asp

i have been thinking about getting one for my WJ for a wile

Speedo change?

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