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    Mph

    My mph is 2-3 mph faster than my gps confirms. In order to make the reading more accurate do I program in a smaller or larger wheel size?

    #2
    Bigger,

    i had this issue as well, the miles were clocking up too fast, i made a mistake in the wheel size.

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      #3
      Originally posted by CharlesZ View Post
      My mph is 2-3 mph faster than my gps confirms. In order to make the reading more accurate do I program in a smaller or larger wheel size?
      Smaller. The speedometer measures RPM and multiplies that by wheel circumference, so you want to tell it you have a smaller wheel which covers less ground per RPM.

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        #4
        And if you want to compute exactly by how much, calculate the factor by doing the reported speed divided by the real speed you were running when you noticed the difference.
        For example if you bike speedometer was reporting 20mph, and in fact you were doing 17mph, the multiplying factor would be 0.85 (17/20).
        You then apply the same factor to your wheel diameter. For example if you wheel was set to 27", set it to 27 x 0.85 = 22.95

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