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Modifying speedometer for varying revolutions per minute

Discussion in 'Prius c Accessories and Modifications' started by actiondonkey, Jun 4, 2014.

  1. actiondonkey

    actiondonkey Member

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    2012 Prius c
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    II
    Has anyone found a way to reprogram the ECU or some other control system to account for the lower revolutions per minute from a larger rim/tire?

    ETA 2 weeks until a road trip to South Florida and I've got a screw in the sidewall of my stock tires. For a couple years now I've been saying I'll get new wheels and tires but never got around to it... I guess now is the time. After exhaustive research I've decided on Konig Feather rims and Michelin Energy Saver A/S tires. Unfortunately the tires are fairly large and aren't available in a lower profile, leading to the speedometer displaying 65mph when it's actually 69.7. Any help would be greatly appreciated!

    Edit - I meant rotations per mile, not revolutions per minute. My bad homies!
     
    #1 actiondonkey, Jun 4, 2014
    Last edited: Jun 4, 2014
  2. mahout

    mahout Active Member

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    For engine rpm its a tachometer
    For different speedometer display its putting new stickers on the speedometer with correct mph at the needle display. If you're going 69.7 mph when the speedometer says 60 your oversize tire is 26.06" in diameter. Thats a 205/70x15 tire; sure you have the conversion right. I'm not sure that size tire would fit.
    If your tires really are that big the easiest thing to do is print new mphlabels for the 10 mph increments and stick over the originals.
    Again, you sure you have a 205/70x15 tire on your Fit. Wouldn't fit mine.
     
    #2 mahout, Jun 14, 2014
    Last edited: Jun 27, 2014
  3. SamanthaC0716

    SamanthaC0716 Active Member

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    I'm also wondering about this. It's going to be a factor in deciding to go with wider wheels. I still want 15", but they'll be wider. I know I'm not gonna be able to have the overall diameter come out exactly the same as stock.



    iPhone ?
     
    #3 SamanthaC0716, Jun 16, 2014
  4. KK6PD

    KK6PD _ . _ . / _ _ . _

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    Let me save you some time. I went through this with my Gen II, even called Toyota.
    NO YOU CAN NOT RECALIBRATE THE ECU!
    If you change overall outside diameter, OD, it will mess with the computer and produce erroneous data.
    The car will not like that!
     
    #4 KK6PD, Jun 16, 2014
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