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  1. #1
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    Tire size conversion help

    Hi everyone, I'm a newbie biker, and I just bought myself a new computer (even managed to install it with no problems!). I'm trying to figure out what my wheel factor is.

    I have a Trek 7.2 FX and it says that I have a wheel size of 700 X 35C. The data point I need to enter is the wheel factor, or the distance in millimeters per one turn of the wheel. Per the instructions, a 700 X 32C has a wheel factor of 2155, so I'm assuming that it will be just a bit higher than that. Any help would be greatly appreciated.

  2. #2
    Mad bike riding scientist cyccommute's Avatar
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    Quote Originally Posted by acuteot View Post
    Hi everyone, I'm a newbie biker, and I just bought myself a new computer (even managed to install it with no problems!). I'm trying to figure out what my wheel factor is.

    I have a Trek 7.2 FX and it says that I have a wheel size of 700 X 35C. The data point I need to enter is the wheel factor, or the distance in millimeters per one turn of the wheel. Per the instructions, a 700 X 32C has a wheel factor of 2155, so I'm assuming that it will be just a bit higher than that. Any help would be greatly appreciated.
    That's about right for a 700C x 32mm. You won't be off by much. If you really want to be accurate, get on the bike, mark the tire with something and ride in a straight line until the mark shows on the pavement. Measure the distance. Perhaps do several tests and average the results. But I'll bet they come out around 2160 +/-0.5
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  3. #3
    Senior Member Bill Kapaun's Avatar
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    Your tire diameter would be 6MM more, so that times PI would be about 19MM more.

    I just "lasso" my tire with a string, and measure the string.
    Even if you are off by "a few" MM, remember that's in over 2000 units. 20 "parts" off is only 1%, which is far more accurate then your car!

  4. #4
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    Thanks for your help! The exact number is 2173.8, so 2174, I had initially but in 2175, so I got pretty close!

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