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Thread: How to change tire size on LL8?

  1. #31
    Joe (Moderator) joecar's Avatar
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    Hi blown4p3, welcome to the forum, excellent first post

  2. #32
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    Welcome to EFILive Dave, glad you made your way over from TrailVoy. Ive only half done the math before, Ill look at redoing it for my friends 04 P10 this week and see if I cant flash it tomorrow when Im borrowing his TB while he tints my SS.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, starting the mods
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  3. #33
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    Thanks for the warm welcome guys!

    Well, for the entertainment of it, I did toss the GPS into the TB tonight. With the stock tires, my speedometer would show about 2 mph faster than the GPS. Makes sense if the pulse count is greater than the actual calculated value. Not that it was be a bad thing. Now, the GPS is reading about 2 mph faster than the speedometer, or a net change of about 4 mph at 70/75. This is also fairly consistent with what the calculated difference would be between the stock 245/70/16s and the new 265/70/16s. A 5% difference at 60 mph in values equals about 3 mph.

    However, the flashscan gave an error when trying to reprogram the computer. The first was the one about needing to be licensed to that vehicle. Ok, no problem, fixed that and tried again. It came up with a different error... but I didn't get a screen shot of it so I'll have to try again tomorrow.
    2003 Trailblazer LS

  4. #34
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    Did you get it working yet? Once it's licensed you shouldnt have any problems flashing it as long as there arent any aftermarket electronics on the databus.
    ~Erik~
    2013 Sonic RS Manual - 1.4L I4T E78, starting the mods
    2008 TrailBlazer SS 3SS AWD Summit White - LS2 E67/T42, bolt ons, suspension, etc.
    2002 Chevy TrailBlazer LT 4X4 Summit White - 4.2L I6 P10, lifted, wheels, etc.

  5. #35
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    After sweating bullets last night when the PCM lost the base program and then finally getting it to recover with another laptop, I stopped working on it. Looks like I probably won't get a chance to try it again until the weekend. I'm committed to putting 4 new struts on our 13 year old Honda this weekend. Since it still has the factory ones on it, I'm sure I'll run into some problems that will have to be addressed before I can mess with the TB again.

    I should mention that the TB is totally stock except for an Airaid filter/tube setup. Stock radio and all.

    If it works, doesn't, or needs some other kind of tweak I'll post up what happens here.
    2003 Trailblazer LS

  6. #36
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    Good post …. nice math !!!

    In the past I had tried various approaches with speedometer calibrations - tire diameter (inches and millimetres) versus manufacturer’s revolutions per mile values.

    I have found the software will make accurate changes to the speedometer calibration, based on tire diameter. If you input an accurate tire diameter, the software will recalculate tire circumference, tire revolutions per mile (this won’t match the manufacturer’s value), and VSS output pulses per mile.

    The values in the Speedo Calculator will appear simultaneously in Imperial and Metric values - how this is displayed in the software will depend on the default settings you have chosen (Imperial versus Metric).

    I would use a little caution in reverse engineering tire diameter from the manufacturer’s revolutions per mile figures - option for rounding and compounding errors to creep into the math equation.

    I will generally confirm the tire diameter for the exact tire being used, and compare this value to the tire diameter of the same tire size from other manufacturers - to eliminate potential error.


    Regards,
    Taz

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