Speedometer Adjustment Questions

ChooChooman74 · **Posted:** Fri Jan 04, 2013 12:20 am

My speedometer is off, it is affecting my GDE Transmission tune, and I want it corrected. I also understand that it is a dealer thing, or someone with a DRBII machine. But I have a few questions that I hope I can get answered, because my local Jeep service writer seems clueless.

1) Some people say that they can only adjust per tire size, and others say they can put Revolutions per Mile. Which is it?

2) Is there a chance that they will try to flash my ECU or TCM?

3) I am figuring that that my computer is calculated for my base tire size of 225/75R16. I am guessing that using torque software, and figuring out RPM, Reporting Speed, and GPS speed, and doing some calculations, I should be able to estimate how many revolutions per minute or approximate tire size my setting should be to correct my speedometer.

Anyone who has adjusted for tire size, help me out here.

arengant · **Posted:** Fri Jan 04, 2013 2:05 am

ChooChooman74 wrote:

My speedometer is off, it is affecting my GDE Transmission tune, and I want it corrected. I also understand that it is a dealer thing, or someone with a DRBII machine. But I have a few questions that I hope I can get answered, because my local Jeep service writer seems clueless.

1) Some people say that they can only adjust per tire size, and others say they can put Revolutions per Mile. Which is it?

2) Is there a chance that they will try to flash my ECU or TCM?

3) I am figuring that that my computer is calculated for my base tire size of 225/75R16. I am guessing that using torque software, and figuring out RPM, Reporting Speed, and GPS speed, and doing some calculations, I should be able to estimate how many revolutions per minute or approximate tire size my setting should be to correct my speedometer.

Anyone who has adjusted for tire size, help me out here.

What kind of issues with the tune are you having? I am thinking about adjusting my tire size to optimize my tcm tune also.

ChooChooman74 · **Posted:** Fri Jan 04, 2013 9:27 am

Shifting too early due to speedo off.

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Joe Romas · **Posted:** Fri Jan 04, 2013 1:41 pm

Look around on the www for a tire sizing chart, some have a "revolutions per mile" for each size :SOMBRERO:

Some of us have found a "pre-f-37" tcm just so it would shift sooner :BANANA:

Isn't that what GDE's transmission tune is supposed to do :?:

ChooChooman74 · **Posted:** Fri Jan 04, 2013 2:27 pm

Speedometer is off so it shifts too early. I have the tow tune to shift 5th at 65 (doing so at 63 though) but at 63, I am doing 60 on the GPS.

I am hoping Sir Sam or Keith chimes in. I want to know for sure what the setting is and how they do it so the stealership gets it right!

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CATCRD · **Posted:** Fri Jan 04, 2013 4:17 pm

You can enter revolutions per mile for the speedo and odo independently.

Go to tirerack.com and find your tires. In the specs page it will tell you the exact revs/mile for your size tire.

ChooChooman74 · **Posted:** Sat Jan 05, 2013 12:33 am

Can they look and tell me what the current settings are?

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Dennis MacGyver · **Posted:** Sat Jan 05, 2013 2:17 am

Keith at GDE, can adjust the TCM to shift anyway you like. Record you shift points, rpm & mph, with a gps and send those stats to him. He can do the change to the ECM over the net but the TCM will have to be sent in to him.

Joe Romas · **Posted:** Sat Jan 05, 2013 9:48 am

"Speedometer is off so it shifts too early. I have the tow tune to shift 5th at 65 (doing so at 63 though) but at 63, I am doing 60 on the GPS."

I found the following on GDE's site about the towing TCM tune.

•This tune engages 4th gear unlock at 35mph, 4th at 46mph and 5th at 70mph.
•Optimized for fuel efficiency in city driving conditions with speeds below 58mph.
• Increased lock-up lowers transmission fluid temps and lock-to-lock shifting is enabled to make the shifts quicker and crisper.
•The tune keeps the trans in 4th gear lockup between 46mph and 70mph, which is perfect for towing heavy loads and mountain driving.
•Additionally, once 70 mph is reached and the shift to 5th is completed, the vehicle can be slowed down to 50 mph and will maintain 5th gear.
•Variations on the lock-up schedule are available upon request for customers with special needs.

I don't totally understand what the second line is saying but could it possibly be what your talking about? To me it does not sound like the small speedometer error with stock tires we all notice should make much of a difference.
And is the 70 MPH shift to 5th in a pedal to the floor situation :?:

For towing my around 3000-3200 pound trailer my "F-37 TCM" that shifts at a indicated 64 mph works well. But for day to day I prefer my "Pre F-37" tcm :jester:

But I have the Euro TC and the "Eco full torque" ecm tune that could be making a difference.
Your speedometer indicated 64 and GPS indicating 60 is exactly what I see too :CAMPING:

I got the above here :POPCORN:

http://www.greendieselengineering.com/s ... e&model=++

CATCRD · **Posted:** Sat Jan 05, 2013 11:17 am

ChooChooman74 wrote:

Can they look and tell me what the current settings are?

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Yes, they can look in the DRB and tell you what it's set to now. But really I think it would be best to get a GPS speed reading and dividing your indicated speed by that to get a correction factor. Apply that to the current rev/mile setting and you will probably get closer than using a rev/mile number off the tire spec sheet.

teckman02 · **Posted:** Sat Jan 05, 2013 11:25 am

have you looked into this http://www.rustysoffroad.com/superlift-s-truspeed-speed-signal-calibrator.html

Sir Sam · **Posted:** Sat Jan 05, 2013 1:38 pm

For a 2006 you need a starscan, which means my DRBIII would do you no good.

There are two settings, one in the ACM and the other in the BCM, the BCM will affect odo, the ACM affect the speedo. You need to enter the revs/mile, but I have found that even entering the revs/mile from actually measuring the tires, or calculating the tires, is typically off, the best way is to read the revs/mile for your current calibration, (typically about 721) and then calculate for what your new one should be.

So lets say your speedo reads 50mph and your GPS reads 46mph, you would do (721/50)=(X/46)

In this case X= 663, note while thats an interesting starting point its going to be low. I've found this same problem when using PI and a measuring tape to calculate the revs/mile.

Typically I recommend calculating the desired revs/mile and then splitting the difference, and using that as a starting point.

(721+663)/2= 692

Do a road test at 50mph and compare to a GPS reading, you can toy with it and adjust it until the speedo reads correct.

Note to do this you need unfettered access to a DRBIII or starscan, or a tech who is willing to work with you.

ChooChooman74 · **Posted:** Sat Jan 05, 2013 1:40 pm

Joe Romas wrote:

"Speedometer is off so it shifts too early. I have the tow tune to shift 5th at 65 (doing so at 63 though) but at 63, I am doing 60 on the GPS."

I found the following on GDE's site about the towing TCM tune.

•This tune engages 4th gear unlock at 35mph, 4th at 46mph and 5th at 70mph.
•Optimized for fuel efficiency in city driving conditions with speeds below 58mph.
• Increased lock-up lowers transmission fluid temps and lock-to-lock shifting is enabled to make the shifts quicker and crisper.
•The tune keeps the trans in 4th gear lockup between 46mph and 70mph, which is perfect for towing heavy loads and mountain driving.
•Additionally, once 70 mph is reached and the shift to 5th is completed, the vehicle can be slowed down to 50 mph and will maintain 5th gear.
•Variations on the lock-up schedule are available upon request for customers with special needs.

I don't totally understand what the second line is saying but could it possibly be what your talking about? To me it does not sound like the small speedometer error with stock tires we all notice should make much of a difference.
And is the 70 MPH shift to 5th in a pedal to the floor situation :?:

For towing my around 3000-3200 pound trailer my "F-37 TCM" that shifts at a indicated 64 mph works well. But for day to day I prefer my "Pre F-37" tcm :jester:

But I have the Euro TC and the "Eco full torque" ecm tune that could be making a difference.
Your speedometer indicated 64 and GPS indicating 60 is exactly what I see too :CAMPING:

I got the above here :POPCORN:

http://www.greendieselengineering.com/s ... e&model=++

I ordered my tow tune to shift at 65. Per GDE website, you can customize the 5th shift point. I probably wont be towing at 65.

I am going to have to take it to the dealer, fork over the cash, and get it adjusted. The desired results would be 60 on the speedo be 60 to 61 on the gps.

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Dennis MacGyver · **Posted:** Sat Jan 05, 2013 3:27 pm

Joe Romas wrote:

Your speedometer indicated 64 and GPS indicating 60 is exactly what I see too

Same here, I'm running BFG AT/KO's 225/85/16, their height is 29.5"

LIBERTYinLIBERTY · **Posted:** Sat Jan 05, 2013 7:14 pm

Talked to Keith at GDE, he told me to reverse calculate the rpm's. So we (Dealer)did that and ended up programing it to 765 rpm's for the 265 75R 16 and it is now within .5 MPH, but the odometer is off approx 9%.

Lanny at Tony Martins Jeep in Platte City, Mo. 816 858 5575

Dealer Charged me $50.00 and took 4 tried to get right....

Dennis MacGyver · **Posted:** Sat Jan 05, 2013 8:21 pm

So that corrects the speedometer (I guess that correction is in the ECM or is it in the TCM ) ??

So where does the odometer get it's information reading from ??
Does the odometer AND the trip meter get their info from the same device (assume nothing when it comes to the CRD) ??

06PeakBagger · **Posted:** Sat Jan 05, 2013 8:34 pm

@LibertyinLiberty, Did the dealer service to correct the speed affect the GDE?

Sir Sam & anyone else who may know can the Snap-on hand held computer VERUS Diagnostic adjust the speed settings? Or is my understanding correct that StarScan is the only game in town for the 2006?

LIBERTYinLIBERTY · **Posted:** Sun Jan 06, 2013 12:12 am

Shifts into 5th @ 65 mph

ChooChooman74 · **Posted:** Sun Jan 06, 2013 11:41 am

LIBERTYinLIBERTY wrote:

Talked to Keith at GDE, he told me to reverse calculate the rpm's. So we (Dealer)did that and ended up programing it to 765 rpm's for the 265 75R 16 and it is now within .5 MPH, but the odometer is off approx 9%.

Lanny at Tony Martins Jeep in Platte City, Mo. 816 858 5575

Dealer Charged me $50.00 and took 4 tried to get right....

Your answer has been the most helpful so far! MANY THANKS!!!

arengant · **Posted:** Sun Jan 06, 2013 2:13 pm

LIBERTYinLIBERTY wrote:

Talked to Keith at GDE, he told me to reverse calculate the rpm's. So we (Dealer)did that and ended up programing it to 765 rpm's for the 265 75R 16 and it is now within .5 MPH, but the odometer is off approx 9%.

Lanny at Tony Martins Jeep in Platte City, Mo. 816 858 5575

Dealer Charged me $50.00 and took 4 tried to get right....

For your application, the 765 rpm for those 265/75 tires is with stock gears not 4.10 right?

Speedometer Adjustment Questions

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