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PostPosted: Fri Dec 11, 2009 7:54 pm 
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1996xj wrote:
Well, I took Towstap's KJ back to the dealer and the Tech. and I decided to go with the largest tire size avalible in the DRB III, which was 235/75/16, the speedo work's great, only off less than 1mph and the shift point's seem better !! :D :D :D


Your Dealer Tech does not know how to use his DRBIII. Yes, there are predefined setting based on tire-size (215/75, 225/70, 235/70, and 235/75, I believe), but there is also an "Other" selection possible where you put in the revolutions per mile (taken from the specifications listed by size per manufacturer at TireRack) that allow you to put in exactly what it should be because the number of revolutions per mile differ per manufacturer (since no two manufacturers' tires are actually the same exact size) and size of the tire -- this is the way that you can do 235/85s, 245/75s, 255/75s, and 265/75s. This does not surprise me, as half of the Jeep Dealers I have run across (2 of 4) in the past 5-years did not know how to do this...

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PostPosted: Fri Dec 11, 2009 8:12 pm 
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I was asking him if there were other ways to imput the data to the BCM/PCM and he said no, The Tech did enter the RPM for the tire size 245/75/16 but that caused the speedo to quit working and the check eng. light to come on. I know with GM there usually is couple differnt ave. He was abel to input the tire size 265/75/16 into my 04 KJ, without a prob. I wanted to grab the DRBIII and try myself but that prob. wouldn't of went over to good !!! :roll: :roll: :roll: :roll:

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PostPosted: Fri Dec 11, 2009 9:11 pm 
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Cobolt-60 wrote:
1996xj wrote:
Well, I took Towstap's KJ back to the dealer and the Tech. and I decided to go with the largest tire size avalible in the DRB III, which was 235/75/16, the speedo work's great, only off less than 1mph and the shift point's seem better !! :D :D :D


Your Dealer Tech does not know how to use his DRBIII. Yes, there are predefined setting based on tire-size (215/75, 225/70, 235/70, and 235/75, I believe), but there is also an "Other" selection possible where you put in the revolutions per mile (taken from the specifications listed by size per manufacturer at TireRack) that allow you to put in exactly what it should be because the number of revolutions per mile differ per manufacturer (since no two manufacturers' tires are actually the same exact size) and size of the tire -- this is the way that you can do 235/85s, 245/75s, 255/75s, and 265/75s. This does not surprise me, as half of the Jeep Dealers I have run across (2 of 4) in the past 5-years did not know how to do this...


I had issues with my 31s. When I went to the dealer I forgot the Rev per mile I had written down on paper so I had the service writer call a tire shop and get a number from them. I got the jeep back and the speedo didn't work, just like with Towstrap's jeep. I went right back and talked directly to the tech and he told me the number he had input, which I knew wasn't the number I had written down. I called my wife and got the correct number directly from Interco and the number he put it in was way off. He tried a few other numbers and he found there was a limit that the KJ could use, limit as in it only accepts a number of rev per mile up to a certain height. I could not take my 35s in and tell them the Revs per mile and have it to work. The 35s number is outside the KJs parameters and the tech said my old 31s were just under the limit. He could be full of crap but the input he entered the first time would leave me to believe he was right because of how the jeep acted.

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PostPosted: Sun Dec 13, 2009 5:14 pm 
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Inc wrote:
I had issues with my 31s. When I went to the dealer I forgot the Rev per mile I had written down on paper so I had the service writer call a tire shop and get a number from them. I got the jeep back and the speedo didn't work, just like with Towstrap's jeep. I went right back and talked directly to the tech and he told me the number he had input, which I knew wasn't the number I had written down. I called my wife and got the correct number directly from Interco and the number he put it in was way off. He tried a few other numbers and he found there was a limit that the KJ could use, limit as in it only accepts a number of rev per mile up to a certain height. I could not take my 35s in and tell them the Revs per mile and have it to work. The 35s number is outside the KJs parameters and the tech said my old 31s were just under the limit. He could be full of crap but the input he entered the first time would leave me to believe he was right because of how the jeep acted.


I can believe that... The 265/75R16s are 32" tires and most seem to be able to make those work (but I woudn't want to try and do them without 4.10 gears... LOL). I am not surprised that the BCM doesn't know what to do with 35" tires...!!! :lol:

I know my General AT2 LT 245/75R16s (30.7" x 9.8") were 679 RPM, and I know the DRBIII was able to take these values. I also know that a Goodyear MT/R in the same size is 676 RPM and the BCM will accept these numbers as well. I don't have any personal experience with any RPM value "lower" than these but I DO know that my "default" when I had my stock Wrangler ST donuts (P215/75R16s) was set at 750 RPM from the factory where if you check the values at TireRack the value from that manufacturer for this size should have been 729 RPM!!! :shock:

It also makes me wonder about the differences between the BCM in the '04 verses '05 models as well...

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PostPosted: Sun Dec 13, 2009 7:24 pm 
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Cobolt-60 wrote:
Inc wrote:
I had issues with my 31s. When I went to the dealer I forgot the Rev per mile I had written down on paper so I had the service writer call a tire shop and get a number from them. I got the jeep back and the speedo didn't work, just like with Towstrap's jeep. I went right back and talked directly to the tech and he told me the number he had input, which I knew wasn't the number I had written down. I called my wife and got the correct number directly from Interco and the number he put it in was way off. He tried a few other numbers and he found there was a limit that the KJ could use, limit as in it only accepts a number of rev per mile up to a certain height. I could not take my 35s in and tell them the Revs per mile and have it to work. The 35s number is outside the KJs parameters and the tech said my old 31s were just under the limit. He could be full of crap but the input he entered the first time would leave me to believe he was right because of how the jeep acted.


I can believe that... The 265/75R16s are 32" tires and most seem to be able to make those work (but I woudn't want to try and do them without 4.10 gears... LOL). I am not surprised that the BCM doesn't know what to do with 35" tires...!!! :lol:

I know my General AT2 LT 245/75R16s (30.7" x 9.8") were 679 RPM, and I know the DRBIII was able to take these values. I also know that a Goodyear MT/R in the same size is 676 RPM and the BCM will accept these numbers as well. I don't have any personal experience with any RPM value "lower" than these but I DO know that my "default" when I had my stock Wrangler ST donuts (P215/75R16s) was set at 750 RPM from the factory where if you check the values at TireRack the value from that manufacturer for this size should have been 729 RPM!!! :shock:

It also makes me wonder about the differences between the BCM in the '04 verses '05 models as well...


That is my big question. The issues I ran across were with my 31" tires, and I thought people had their KJs reprogrammed with 265/75 (32") tires and didn't have issues. I wonder if anyone with an 05+ KJ has tried to program their jeep for 32s. I am sure someone has had it done with 02-04 KJ, right?

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PostPosted: Sun Dec 13, 2009 7:38 pm 
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Inc, I had the 04 done with 265/75/16 = 32 and worked great no issue's !!

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PostPosted: Sun Dec 13, 2009 7:49 pm 
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No help here I believe I had to have mine reprogrammed for 28.5" tall tires for my 265/75's but I had to compensate for 4.10's.


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PostPosted: Sun Dec 13, 2009 8:34 pm 
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tjkj2002 wrote:
No help here I believe I had to have mine reprogrammed for 28.5" tall tires for my 265/75's but I had to compensate for 4.10's.


I find this part of the discussion fascinating....

I since my '04 KJ Sport originally came with 28.5" street tires (215/75), it required reprogramming when I went to 29.5" (245/70) and later 30.7" (245/75) tires. I wonder what the "optimal" combination RPM programming and gears are necessary for "optimization" based on utilization of the vehicle based on the tire-size used (i.e., which profile gets the best mileage, which one gives the most torque, which is the best balance, etc.).

Troy, how did you figure that your BCM needed to be programmed for 28.5" tires to compensate for the 32" tires you were using with your 4.10 gears?

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PostPosted: Sun Dec 13, 2009 9:38 pm 
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Cobolt-60 wrote:
tjkj2002 wrote:
No help here I believe I had to have mine reprogrammed for 28.5" tall tires for my 265/75's but I had to compensate for 4.10's.


I find this part of the discussion fascinating....

I since my '04 KJ Sport originally came with 28.5" street tires (215/75), it required reprogramming when I went to 29.5" (245/70) and later 30.7" (245/75) tires. I wonder what the "optimal" combination RPM programming and gears are necessary for "optimization" based on utilization of the vehicle based on the tire-size used (i.e., which profile gets the best mileage, which one gives the most torque, which is the best balance, etc.).

Troy, how did you figure that your BCM needed to be programmed for 28.5" tires to compensate for the 32" tires you were using with your 4.10 gears?
The tech,actually the service writer(a real good friend of mine,has built more offroad vehicles then I can count) did the math,I believe it was the rpm's for a 28.5" tire,it could have been a 28" tire,anyways it was a smaller tire then what came factory on my KJ which was the 235/70's.


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PostPosted: Sun Dec 13, 2009 10:43 pm 
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tjkj2002 wrote:
Cobolt-60 wrote:
Troy, how did you figure that your BCM needed to be programmed for 28.5" tires to compensate for the 32" tires you were using with your 4.10 gears?
The tech,actually the service writer(a real good friend of mine,has built more offroad vehicles then I can count) did the math,I believe it was the rpm's for a 28.5" tire,it could have been a 28" tire,anyways it was a smaller tire then what came factory on my KJ which was the 235/70's.


This is just amazing!!! Since 28.5" (215/75) is a valid factory size, and available as a choice in the DRBIII and has a RPM of 729, while the RPM for 265/75s is generally around 650 (BFG A/T KOs in that size are 654 RPM), that is over a 75 RPM difference!!!!! It is amazing to me that the gearing difference of going from 3.73s to 4.10s can compensate for that!!!! How far off is the speedometer?

I have noticed that whether I had on 245/70s or 245/75s, the shift points (with the manufacturers listed RPMs used after the pinion index reset) are about 300 rev/min higher than they were when stock (shifting at 2800 rpms as opposed to 2500 rpms), which is still a heck of a lot better than where it was shifting before the reprogramming (~3000-3200 rpms!!!)

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Last edited by Cobalt-60 on Sun Dec 13, 2009 11:08 pm, edited 1 time in total.

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PostPosted: Sun Dec 13, 2009 10:52 pm 
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Information like this really confirms the need to regear when upsizing to a larger tire.

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PostPosted: Mon Dec 14, 2009 12:20 am 
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I need to talk to the tech again and see about getting it set for my 35s it sounds like.

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PostPosted: Mon Dec 14, 2009 12:32 am 
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Inc wrote:
I need to talk to the tech again and see about getting it set for my 35s it sounds like.
What gears did you go with again? If it was 4.88's(If I remember correctly) you should only need to have it reprogrammed for 32" tires.How far is your speedo off now?

I'm so glad I don't have to worry about that anymore,I can adjust my speedo while driving,it's dead on with my GPS.


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PostPosted: Mon Dec 14, 2009 12:43 am 
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tjkj2002 wrote:
Inc wrote:
I need to talk to the tech again and see about getting it set for my 35s it sounds like.
What gears did you go with again? If it was 4.88's(If I remember correctly) you should only need to have it reprogrammed for 32" tires.How far is your speedo off now?

I'm so glad I don't have to worry about that anymore,I can adjust my speedo while driving,it's dead on with my GPS.


I went with 4.88s. There is a local company that specializes in reprogramming off road rigs, Infinite Velocity Motorsports, and I have been told to see them about a fix for it.

At 70 mph, the speedo reads 57 or so. It gets farther off as I go faster, so at slower speeds it is only about 5 off, say around 35 or 40 mph.

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PostPosted: Mon Dec 14, 2009 6:42 pm 
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I went to the shop today and talked to the techs there. They said to get it exact, much closer than what the dealer could do, they need a tuning programmer. They called Diablo Motorsports, I think that was who it was, about the availability of a tuner, and they said they would be releasing one early next year. I may talk to the dealer again to see their take on reprogramming my speedo.

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PostPosted: Mon Dec 14, 2009 7:14 pm 
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Inc wrote:
I went to the shop today and talked to the techs there. They said to get it exact, much closer than what the dealer could do, they need a tuning programmer. They called Diablo Motorsports, I think that was who it was, about the availability of a tuner, and they said they would be releasing one early next year. I may talk to the dealer again to see their take on reprogramming my speedo.
http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/category_id=287/home_id=59/mode=prod/prd126.htm

What I used and my speedo is dead on.


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PostPosted: Tue Dec 15, 2009 12:46 am 
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tjkj2002 wrote:
Inc wrote:
I went to the shop today and talked to the techs there. They said to get it exact, much closer than what the dealer could do, they need a tuning programmer. They called Diablo Motorsports, I think that was who it was, about the availability of a tuner, and they said they would be releasing one early next year. I may talk to the dealer again to see their take on reprogramming my speedo.
http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/category_id=287/home_id=59/mode=prod/prd126.htm

What I used and my speedo is dead on.

For some reason I thought your speedo fix worked in connection with your atlas, I never really read the speedo fix thread in the SFA forum I guess. :oops:

Thanks for the link.

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PostPosted: Thu Jan 07, 2010 2:35 pm 
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Inc wrote:
tjkj2002 wrote:
Inc wrote:
I went to the shop today and talked to the techs there. They said to get it exact, much closer than what the dealer could do, they need a tuning programmer. They called Diablo Motorsports, I think that was who it was, about the availability of a tuner, and they said they would be releasing one early next year. I may talk to the dealer again to see their take on reprogramming my speedo.
http://www.dakotadigital.com/index.cfm/page/ptype=product/product_id=126/category_id=287/home_id=59/mode=prod/prd126.htm

What I used and my speedo is dead on.

For some reason I thought your speedo fix worked in connection with your atlas, I never really read the speedo fix thread in the SFA forum I guess. :oops:

Thanks for the link.


Wouldn't using the Dakota Digital converter cause problems with ABS? The ABS controller would see different speeds from the rear axle and front wheel sensors.

That's only on an '02-04 of course. On an '05+ it would be even more complicated with one sensor per wheel.

I'd think you would need on converter for each wheel speed sensor to get proper ABS functionality.

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 Post subject: Re: Speedometer calibration and shifting points
PostPosted: Thu Jan 07, 2010 3:47 pm 
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I am not sure that '05's would have one sensor per wheel. I think that happened in '06 when ABS became standard. I do not have ABS on my '05.

BTW: My shift points are whatever I want them to be...

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 Post subject: Re: Speedometer calibration and shifting points
PostPosted: Tue Jan 26, 2010 6:41 am 
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found out over the weekend that my reset went backwards. i had stock goodyear 225 75 16's on...then i went lifted on rancho and ome's with kumho road venture at's 245 75 16's. with no pinion reset i was off about 2.5 to 3 mph at 60. went to jeep got a pinion reset and ended up 6 mph off at 60. wondering if anyone has had this happen or if i should just go in cussing like a sailor (helps that i am one) any help would be great. at least they have to fix it for free

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