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Thread: Speedometer Calibration

  1. #1
    Potential Tuner
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    Aug 2018
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    Speedometer Calibration

    Hello! Help correctly calibrate the speedometer! Car Hummer H2, 2009, the stock wheels were 305/60 R20. Since this restail was the main pair with a gear ratio of 3.73. When the firmware was read, the SPEEDO tab indicated
    Stock.png
    What's strange, the indicated number of turns per mile does not match the installed wheels. Let me remind you that the tires from the factory were 305/60 R20, which corresponds to 34.4 "= 586 revolutions per mile .The set value rather corresponded to rubber 33.2".

    After the upgrade, I installed the main pairs with a ratio of 4.56 and the rubber put 37x12.5 R20. The site of the manufacturer of rubber Nitto Radge Grapper indicated that the true size of 36.77 and 565 revolutions per mile. When performing the automatic substitution, the following values ​​were obtained:
    after update.png

    The values ​​are different, although if you count through the calculator on the Internet, the program almost correctly substitutes the values ​​of 549, instead of 545.

    All would be nothing, but the speedometer shows at 10 more real speed.
    How correctly to make calibration? Maybe the machine does not perceive the changes made? On the Limiter tab, source changed from GMLAN to Calibration.

    Thanks for the help.
    Last edited by AndretZak; 08-21-2018 at 04:15 PM.

  2. #2
    Advanced Tuner
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    Apr 2015
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    302
    I'm curious, why do you show 36 pulses per rev?

    I thought most GM's were 40. It very well could be the cause of your 10mph difference...

  3. #3
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    This was indicated in the firmware. When I downloaded the firmware of other years from the repository, I noticed this too. Before 2008, 40 are indicated, and 2009 is already worth 36, can they replace the speed sensor?

  4. #4
    Advanced Tuner
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    Apr 2015
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    I checked a 2009 silverado and it was at 40 also, honestly, I would change it and see if it fixes your problem. If it doesn't, change it back...

  5. #5
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    I changed to 40. The readings of the speedometer steel were much more accurate, but the car started to go badly! I click on the accelerator, the engine rises, and the car barely begins to accelerate. Then, on the contrary, it starts very abruptly. I assume that it's easy to change from 36 to 40, this is not enough, you need to adjust the transmission box. Has returned back 36.

    Do you know if it's possible to get a factory firmware for my car somewhere? I just reviewed all the firmware downloaded from this site for Hummer H2 and everywhere it costs 36. In the last post I was wrong. So I would like to look at a completely original firmware. Can you download it on the GM website?