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Speedo issues after bigger tires and regear

Discussion in 'Technical Chat' started by jacobigindi, Oct 18, 2013.

  1. Oct 18, 2013 at 7:22 AM
    #1
    jacobigindi

    jacobigindi [OP] Well-Known Member

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    Hey everyone. So I upgraded the tires on my 5 lug from the stock 27" to 32" recently and I experienced the expected change in my speedo and odo accuracy. Since the new tires were about 19% bigger than stock, the speedo read about 19% too slow. Then I regeared to 4.10 and expected the speedo accuracy to go back to being only about 4% off based off the math in this thread: http://www.tacomaworld.com/forum/performance-tuning/155144-true-speed-after-regear-formula.html. But i was verifying it with a GPS speedo on my phone and it's still about 15 percent off. Anyone know why this could be?
     
  2. Oct 18, 2013 at 7:31 AM
    #2
    Paleus

    Paleus Well-Known Member

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    I think the speedometer is based on wheel speed. Changing your gears didn't affect your wheelspeed relative to the axle, just how fast the engine is turning. Your wheels are still turning 19% different than the distance your speedo thinks you are traveling. The gear change put your RPMs about back to normal, but your bigger tires are still covering more ground with each revolution.
     
    Last edited: Oct 18, 2013
  3. Oct 18, 2013 at 7:56 AM
    #3
    jacobigindi

    jacobigindi [OP] Well-Known Member

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    darn, i thought it was before the driveshaft. Well at least I have more power now haha
     
  4. Oct 18, 2013 at 8:00 AM
    #4
    Hairy Taco

    Hairy Taco Bush Pusher

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    Exactly, you must be happy to have the power back, that is a significant change in wheel diameter
     
  5. Oct 18, 2013 at 8:03 AM
    #5
    bjmoose

    bjmoose Bullwinkle J. Moose

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    hypertech in-line speedometer calibrator.
     
  6. Oct 18, 2013 at 8:04 AM
    #6
    Delmarva

    Delmarva Mayor of TW

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    this... easy install and setup
     
  7. Oct 18, 2013 at 8:12 AM
    #7
    jacobigindi

    jacobigindi [OP] Well-Known Member

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    hmmm I'm very seriously considering this. Found it for 200 with free shipping on autoanything.com.
    Any other feedback on this thing?
    Also, if i have an ultragauge, will the calibrator correct the speed and mileage data going to it through the OBDII?
     
  8. Oct 18, 2013 at 9:06 AM
    #8
    bjmoose

    bjmoose Bullwinkle J. Moose

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    When you install it, check and double check that you've connected it the right way. Unlike many modern "idiot proof" plugs, it's possible to plug this unit in backwards. That's not a reason not to do it - just a reason to be careful.

    I haven't used it with an Ultragauge, so I can't say for sure. You could call tech support at Hypertech and ask them.
     
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