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  1. #1
    Join Date
    Mar 2008
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    Setting up my speedometer

    Hey guys,
    I just started riding my bike again. It's a Trek 800 with suspension fork.

    Anyway, I have some sort of a C3 computer on it (very simple, displays time, speed, trip meter and odometer).
    The wheel size is set at 2124
    I assume this is mm?
    In which case I should measure the rolling diameter of my wheel and put that in, in mm?
    It's a 26" wheels, so 26 * 254 * 3.14 = what I should enter in mm or does this not include the tyre?

  2. #2
    Senior Member twinquad's Avatar
    Join Date
    Oct 2007
    State College PA
    My Bikes
    Cannondale T2000, Dean el Diente
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    Different 26" tires have different circumferences, from 1950 mm for 26 x 1.25 to 2170 mm for 26 x 3.00, according to the table of estimated circumferences in the Cateye instruction sheet I have (download PDF here).

    You can roll and measure if you want to be more precise. Lay a tape measure on the floor, line up the valve stem (or some other identifiable point) with zero on the tape, and roll until the stem is at the bottom again, and read where you are on the tape.
    2008 Salsa Casseroll (commuter)
    2002 Dean el Diente (road)
    1996 Trek T100 (tandem)

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