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  1. #1
    Jr. Engineer moosetags's Avatar
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    Jan 2008
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    Santa Rosa Beach, Florida, in the Florida Panhandle, so far out that we are in the Central Time Zone
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    259

    Default Speedometer Is Out of Sync

    I recently upsized the tires on my '04 Suburban 2500. I went from the stock 245's to 265's. This increased the circumference by about 1.5" to 31". This change put my speedometer/odometer off by about 5%. At 70mph on the GPS, my speedo is showing 67mph. I have also done a couple of measured miles on the highway, and the odometer is also shy by about 5%.

    I have been to the GMC dealer twice and asked the to make the proper adjustment. They said that it was done, but the speedo is still off.

    Are there any suggestions out there as I am about ready to go to 265's on my '05 Yuk XL 2500.

    Thanx.
    Brian McCabe
    Santa Rosa Beach, Florida
    '05 Yukon XL 2500 Quadrasteer
    '11 Silverado 3500

  2. #2

    Default

    I am not sure if you can really do much other than getting the computer adjusted for the right tire size. I have 285s on my suburban and I have gotten my computer adjusted to the tire size and the speedometer is exact until i start going past 50mph, once i get past that there tends to be a 3-4mph difference in actual speed.
    K1500 5.7L Chevy Suburban
    290000+ miles
    K&N CAI
    Black Bear Performance Tune
    TCI Servo and Shift Kit
    Long Tube Ceramic Pacesetter Headers
    Custom Side Swept Dual Exhaust
    Dual 2.5in electric DMH Performance Exhaust Cutouts
    BFG A/T 285s

  3. #3

    Default

    Ya i had mine calibrated for 35's and mine has a sweet spot also past 65 on gps it starts to lose track and get behind by a couple i think its the syntrifical force thing as the tires grow DONT know that for sure just one of many guesses

    99 tahoe 2 dr. 4x4 7.4 4L80-e NP246, SAS, dana 60 hp, sterling 10.5 rear, gibson headers, and alot of tricks of the trade !!!!!!IF YOU'RE NOT CHEATING YOUR NOT TRYING!!!!!!!!

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