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  1. #1
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    tire size and speedometer accuracy

    What is the difference between a 26" (590mm) size tire and a 26" (650mm) tire? How much would this effect a speedometer if a 650 mm rated speedo was put on a 590 mm tire?

  2. #2
    Videre non videri
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    It would give a +10% error in speed and distance.

  3. #3
    AEO
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    can't you set the tire size on the computer?
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    This is a vintage item for a vintage bike. No adjustments. Thanks for the replies.

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    Senior Member Bill Kapaun's Avatar
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    Which 650?
    A 650A is a 590MM rim and is a nominal 26" tire dia. (26x1-3/8)
    A 650B is a 584MM rim and is a nominal 26" tire dia. (26x1-1/2)
    A 650C is a 571MM rim and is a nominal 24.5" tire dia. (26x1)

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    It just says 650mm?

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    Pretty easy to check this if you can find an accurately measured mile (shorter distance would work, but a mile is big enough to be pretty accurate and roads often have mileposts). Just ride the distance once or more, then see what the computer gives you and work from there.

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    Quote Originally Posted by bobn View Post
    What is the difference between a 26" (590mm) size tire and a 26" (650mm) tire? How much would this effect a speedometer if a 650 mm rated speedo was put on a 590 mm tire?
    Easy to check (relatively).

    Put one tire on, put a line of toothpaste down, ride over it. Measure the distance between the marks.

    Repeat on the other tire.
    Eric

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