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odometer incorrect

Discussion in 'Technical Q&A' started by climb, Oct 30, 2012.

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  1. climb

    climb F1 Rookie

    Sep 19, 2006
    4,866
    Atlantic Beach Fl
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    Stuart K. Hicks
    #1 climb, Oct 30, 2012
    Don't know how long it's been keeping inaccurate mileage but took the same drive the 308's odometer measured as 7.0 miles in my two other cars and both read 5.5 miles.

    Always felt it was giving the car more miles than it was actually driving and suspected it was registering kilometers but a translation of 5.6 miles to kilometers would be 8.8 or so. Must just be off.

    What vendor should I send it to?

    Thanks
     
  2. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    #2 Steve King, Oct 30, 2012
    What size tires are you running. Are they the same OD as the OEM tires/wheels. If smaller then this could be your problem. If same as OEM then you either need to get the speedo calibrated or the sending unit checked.
     
  3. climb

    climb F1 Rookie

    Sep 19, 2006
    4,866
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    Stuart K. Hicks
    #3 climb, Oct 30, 2012
    Oh jeez. Didn't even think about that. Car came with the original 14 inchers. Put the QV's on years ago. That must be it.

    Thanks
     
  4. BigTex

    BigTex Seven Time F1 World Champ
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    Dec 6, 2002
    79,404
    Houston, Texas
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    Bubba
    #4 BigTex, Oct 30, 2012
    But that would indicate your wheel/tire combo went SMALLER overall?
     
  5. climb

    climb F1 Rookie

    Sep 19, 2006
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    Atlantic Beach Fl
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    Stuart K. Hicks
    #5 climb, Oct 30, 2012
    Oh man, now your really throwing a wrench into the chain. So your saying that it should show less mileage than actual with the bigger wheel/tire combo? Not more as it is now?
     
  6. Crowndog

    Crowndog F1 Veteran

    Jul 16, 2011
    7,042
    Fairfield,Pa
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    Robert
    #6 Crowndog, Oct 30, 2012
    I believe I have read that these speedometer/odometer systems in our cars can be susceptible to electrical noise or spiking from ignition sources etc. that could be adding pulses to the pulse stream from the sender maybe causing false higher readings then normal speeds. Maybe. Also, failing diodes in the alternator have also been associated with false readings and can ruin a speedo. This thread which is long covers most of this : http://ferrarichat.com/forum/showthread.php?t=329231&highlight=speedometer+calibration
     
  7. DanS*

    DanS* Karting

    May 29, 2012
    218
    Manhattan Beach, CA
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    Dan
    #7 DanS*, Oct 31, 2012
    No. If you have a bigger diameter tire, then the car travels further with each revolution than the original. So, you're traveling further than odometer reads. You are also going faster than the speedometer reads!
    All that said, I doubt that you're tire diameter is 20% bigger.
     
  8. BigTex

    BigTex Seven Time F1 World Champ
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    Dec 6, 2002
    79,404
    Houston, Texas
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    Bubba
    #8 BigTex, Oct 31, 2012
    Depending on actual tire selection, I'd bet your combo on 16" rims is actually a smaller outer diameter, due to the modern short sidewall..

    That would agree with your variance...

    Just drive it!! :D :D

    Of course, depreciation is gonna kill you....:D
     
  9. tomberlin

    tomberlin Formula Junior
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    Apr 9, 2005
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    tom berlin
    #9 tomberlin, Oct 31, 2012
    Palo Alto Speedo

    Tom
     
  10. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    #10 Steve King, Oct 31, 2012
    The OEM 14" wheel was a 215/70-14 which has a dia. of 25.9" and turns at 803 revs per mile. What size tires are you running.
     
  11. climb

    climb F1 Rookie

    Sep 19, 2006
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    Stuart K. Hicks
    #11 climb, Oct 31, 2012
    225/60/15 rear

    215/60/15 front
     
  12. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    #12 Steve King, Oct 31, 2012
    The 225/60-15 should be around 25.6" in dia and the rev per mile is 811. They are smaller then the OEM size of 215/70-14 but I don't think the difference would cause your millage error. Are you sure they are 15" and not 16"
     

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