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Thread: Changing Tire Size and Rear Gear Ratio on 2015 Mustang GT

  1. #1

    Changing Tire Size and Rear Gear Ratio on 2015 Mustang GT

    I looked on the forum about changing the gear ratio and tire size and I get conflicting info. Can you change this in VCM Editor to Calibration instead of Learn from BCM or do you leave the switches set to Learn from BCM and change them in VCM Scanner? Also do I need to adjust the N/V Base or will this be done automatically when using VCM Scanner.

  2. #2
    HPT Employee Eric@HPTuners's Avatar
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    Leave the stuff in Editor to stock, and program the tire size and axle ratio via Special Functions in VCM Scanner.
    Eric Brooks
    HP Tuners, LLC

  3. #3
    Eric what about the N/V Base?

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    Advanced Tuner
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    Thanks for info

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    Quote Originally Posted by Eric@HPTuners View Post
    Leave the stuff in Editor to stock, and program the tire size and axle ratio via Special Functions in VCM Scanner.
    Is there any downside to using the editor? I'm guessing you just need to actually do math?
    Knock Retard is the reduction or prevention of knock by lowering ignition timing:

    (+) Adding Knock Retard = Reducing Timing. PCM is seeing knock.
    (--) Lowering Knock Retard = Increasing Timing. PCM isn't seeing knock.
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    Senior Tuner veeefour's Avatar
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    Quote Originally Posted by blackbolt22 View Post
    Is there any downside to using the editor? I'm guessing you just need to actually do math?
    Tested both - no difference whatsoever.

  7. #7
    Veefour I seen a post on the forum about a user that had a 2019 Mustang GT and it was throwing a hill assist error and causing some more issues, he said the fix was to use the scanner to make the changes for gear ratio and tire size however if you are remote tuning cars i dont see how it would be possible if you couldn't use the VCM editor to make the changes.

  8. #8
    Senior Tuner veeefour's Avatar
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    Never had any DTC like that. People claim a lot of stuff, sometimes not knowing the problem is somewhere else.

    You can use ECU tire and gear ratio calibration it works just fine - I've tried both and it felt the same.

    If you remote tune, your customer still need to use a tuner device - MPVI, nGauge, SCT all have the ability to change the bits in BCM.
    I'm not sure if the BCM bits are ignored completely, should you chose to use ECU data. ECU data offers some wiggle room, BCM does not.

    S197 was MPH based and it took VSS signal form ABS module over CAN. S550 is OSS based and it grabs OSS internally - much faster.