SPEEDO ADJUSTMENT

thebenagade · **Posted:** Sat Feb 24, 2007 10:53 am

I am am going to bet getting my tax money back soon and I have gotten the all clear from my wife for a lift, tires and wheels for the libby. I am going with 245/75/16 tires. Now to the big question, my wife is a speeder, big time and drive the jeep most of the time. With the increase in tire size the speedo will be off and I was wondering if anybody has their speedo corrected. I will not be doing gears for a while so I need to try to have the speed corrected before she come home with a big ticket because she forgets about the speed differance.

Jeepjeepster · **Posted:** Sat Feb 24, 2007 11:35 am

My GPS says that my Speed-o is right on with the 245/70/16 tires. I guess it was off alittle with the stock tires. The dealer must correct the speed-o. They hook it up to a computer and change the Rev's per mile I believe.

You mention she is a speeder...She may loose some of that speed with the bigger tires.

What lift do you plan on getting?

2006 KJ · **Posted:** Sat Feb 24, 2007 1:35 pm

i was wondering the same question.. im planning on the frankenlift and 265/75/16's.. and im pretty sure it would throw off my speed-o. did you say that the dealer can correct this problem? and if so.. would it void your warrenty???

tjkj2002 · **Posted:** Sat Feb 24, 2007 1:52 pm

Yes a dealer can recalibrate the speedo,they just need the the old tire size and the new tire size.Some dealers will say that it can't be done but it can,had mine done after getting 265's and 4.10's,cost me $59.99.As for the warrenty,it won't effect it,now the lift and tires may have a dealer screaming about warrenty.

thebenagade · **Posted:** Sat Feb 24, 2007 2:03 pm

I think I am going to go with the skyjacker 2.5, now that I think about it the speedo reads about 4mph faster than the actual speed. that of course is and unofficial guess. I got that from the construction zone on the highway near the house.

OzLtd · **Posted:** Sat Feb 24, 2007 6:46 pm

tjkj2002 wrote:

Yes a dealer can recalibrate the speedo,they just need the the old tire size and the new tire size.Some dealers will say that it can't be done but it can,had mine done after getting 265's and 4.10's,cost me $59.99.As for the warrenty,it won't effect it,now the lift and tires may have a dealer screaming about warrenty.

I tried that as well tjkj but it depends on what model KJ you have. With my last 2003 V6 Renegade, when we plugged in the DRBII unit, it gave us 3 tyres size options to chose from, but I had 245/75/16 on that KJ as well and we chose the closest as it didnt have the exact size.

Now I have a late 2005 built LTD CRD and we tried the exact same thing but it only had 1 choice, as that wheel/tyre combo (17" for LTD's) was the only factory combo available.

talk about bummed out.......... :oops:

I havent looked into this much but can we get the speedo cog thingy changed on the output of the Tcase like the XJ guys do ? Same Tcase afterall ?

unixxx · **Posted:** Sat Feb 24, 2007 7:34 pm

The Liberty's NP231/242 has no speed sensor because the computer gets the speed off a tone ring next to the ring gear. A company makes a kit that can intercept a transfer case speed signal and change it, but I'm not sure if it'll work with our differential's tone ring.

tjkj2002 · **Posted:** Sat Feb 24, 2007 8:31 pm

When I got my speedo recalibrated the tech used the DRBIII and changed the program that calculates the speed for the speedo,it had the 2 preset tire sizes but skipped them and had to punch in new numbers for the PCM.Like I said some dealers wll say "huh?",you need to find a tech that knows the jeep system really good(they are hard to find,trust me).

KJ04 · **Posted:** Sat Feb 24, 2007 9:39 pm

Yeah, my dealer told me they only had 2 size options. I called another dealer and they said no problem, bring it in. Then set it to reolutions per mile.

thebenagade · **Posted:** Sat Feb 24, 2007 11:33 pm

I took it in today for the BCM recode/reflash tsb and talked to service manager. We got on the subject of lift and tire size. I told him the way I understand the warranty info in the owners manual the only way to completely void the warranty is to mess with the speedometer/odometer. Obviously they won't warranty any after market parts I install. He agreed and when I asked him about calibrating my, he look at me kinda wierd (I'm pretty sure his eyes crossed) and said I will have to ask the tech if that is possible. After that I didn't push the issue cause I didn't want him to faint or something so I went outside to look at some of the new jeeps on the lot, when I saw something that caught my eye in the employee parking area.

It was a well used TJ. Big lift, big tire, lots of lights,winch, and lots of trail pinstriping, with crud in all the nooks and crannies. I ran back inside and asked the service manager who owned the jeep. He told me that it was the tech that was working on my libby. I think i even said woohoo. He let go back and talk to him and it just so happens that his dad has a lifted libby and he can do my speedo with out any problem at all. the more i thought about it the more I started to think it wasn't going to be worth the hassle of lifting and tires for the price of the tickets that for sure would have followed due to the inaccurate speed reading.

SRotblat · **Posted:** Sun Feb 25, 2007 2:49 am

There are presets for the various OE tire sizes built into the ECU, but the dealer can edit those specs for ANY sized tire. Anyone telling you that it can not be done should be avoided.

My KJ is still using the 235/70-16 setting but with the 265/70-16 tire revolutions per mile. The dealer was nice enough to change it for free when they mounted my tires...too bad they are now out of buisness :cry:

OzLtd · **Posted:** Sun Feb 25, 2007 4:14 am

tjkj2002 wrote:

When I got my speedo recalibrated the tech used the DRBIII and changed the program that calculates the speed for the speedo,it had the 2 preset tire sizes but skipped them and had to punch in new numbers for the PCM.Like I said some dealers wll say "huh?",you need to find a tech that knows the jeep system really good(they are hard to find,trust me).

So is it the actual DRBIII's capability that can change it, or the parameters built into the cars' ECU/PCM ?

I might have to talk to the guys again.

SPEEDO ADJUSTMENT

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