Larger tires and speedometer/odometer variation

Discussion in 'General Chevy & GM Tech Questions' started by Boxman7481, Oct 22, 2009.

  1. Boxman7481

    Boxman7481 Member

    With larger than stock tires installed on my Colorado the speedometer is 4-5 MPG less than actual at speeds of 65-75 MPG (checked with GPS).

    How does this affect the odometer? Am I putting more miles on my truck than actual??
  2. daweinah

    daweinah Rockstar 100 Posts

    Hmm, your wheels have a larger circumference, so they are traveling further per every rotation of the wheel, so I think your odometer would actually read less?

    EDIT: So yes, if your wheel circumference got 10% longer, you will have traveled 110 miles when your odometer says you've been 100. Would probably throw off your DIC readings too. Wonder if that can be adjusted..?
    Last edited: Oct 23, 2009
  3. Thundare

    Thundare Rockstar 100 Posts

    Yes this can be done by changing the gear in i think the transfer case to match the size of your new tires.
  4. XS ive

    XS ive Rockstar 100 Posts

    I believe you can also modify the ECU to compensate for larger tires by changing shift points as well as speedo/odo readings??
  5. canislupis69

    canislupis69 Epic Member 5+ Years ROTM Winner 5000 Posts

    You can adjust for the tire size (and gear size if you ever change gears) with a hand held tuner. I used a hand held tuner to adjust my speedo for my 35 inch tires and my gear change from 3.73 to 4.56. I used a garmin and kept adjusting with the hand held until my speed was dialed in perfect.

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