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  1. #1
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    Tire Size and Computer Help? WTF mate!

    Picked up a Cateye Mirco Wireless for my new MTB. I'm setting it up and realize that my tire size is not listed in the setup chart. I've got 26x2.25 inch tire up front, but the chart skips me going from 26x2.125 to 26x2.35. So I dialed in the 26x2.125. Will this adversely affect the data reported?

    And what about them suckers with 29" tires, they're not listed at all!

    Let me know what you guys think. Thanks in advance.

  2. #2
    trail rat
    Reputation: slocaus's Avatar
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    Here, post 2 has this link.

    Sheldon Brown, 15 ways to calibrate your cyclocomputer,
    http://www.sheldonbrown.com/cyclecom...libration.html
    Last edited by slocaus; 05-04-2008 at 04:15 PM.
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  3. #3
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    Ok I don't know for Cateye, but every other cycle meter I had, had bike size in millimeters (or inches), and never in tire size, and to be honest, I doubt Cateye is any different.
    So I'm really sorry to be nasty now, but is it so hard to calculate bike size, when you measure radius of your bike? So suckers with 29" tires, or with tires, others then those 5 specified in manuals, normally do this... or they bring computer back to store, exchanging it for water battle, because they are too stupid to use it.
    Sorry but is it really so damm hard to turn some logical thinking on?

  4. #4
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    Quote Originally Posted by silkworm13
    Picked up a Cateye Mirco Wireless for my new MTB. I'm setting it up and realize that my tire size is not listed in the setup chart. I've got 26x2.25 inch tire up front, but the chart skips me going from 26x2.125 to 26x2.35. So I dialed in the 26x2.125. Will this adversely affect the data reported?

    And what about them suckers with 29" tires, they're not listed at all!

    Let me know what you guys think. Thanks in advance.
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  5. #5
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    Measure from your hub to your outer tire, that's your radius r. Use the following math formula to calculate your tire circumference, 2 * (3.141) * r = c

    If you measure in inches and you need it in centimeters (I think that's what the cateye uses) take c from above c * 0.0254 * 10 should give you number of centimeters circumference.

    Warning use at your own risk, it's been a while since I've done these conversions regularly :-)

  6. #6
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    Dude, noob here - I didn't even know you could enter a size other than the options they had in the instructions. Nor did I know what the 4 digit number even was, i thought it was some generic code or something. Again, this is my first bike since I was 10 - learning this all for the first time.

    Thanks for the advice though, dick... (referring to RJend and Primoz, not INCO and slocaus, you guys are cool)

  7. #7
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    Quote Originally Posted by silkworm13
    Thanks for the advice though, dick... (referring to RJend and Primoz, not INCO and slocaus, you guys are cool)
    Dick? It really isn't my fault your logic thinking doesn't exist, or if you don't know how to read manual. In Cateye manual (which is available at http://www.cateye.com/en/manuals/66) it clearly says:
    Setting the wheel circumference
    (1) How to measure wheel circumference
    Measure the radius R (cm) with the rider on the bicycle as shown in Fig.4, and calculate the wheel circumference L (cm) using the following formual:
    L = 2 * Pi *R = 6.283 * R (cm)
    Or, paint a mark on the ground contact surface of the wheel, and directly obtain the wheel circumference by measuring the distance between the marks printed on the ground.
    So noob and first time biking or not, setting wheel size is not rocket science... at least I didn't think until now, it is.

  8. #8
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    I had the same problem. Its basic math. The 26" x 2.25" is equal to 2077. You just have to figure out the fudge factor from the chart to figure out in between sizes.

  9. #9
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    26" x 2.125" = 2070

    26" x 2.35" = 2083

    26" x 2.25" = =2077

  10. #10
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by Pistol79
    I had the same problem. Its basic math. The 26" x 2.25" is equal to 2077. You just have to figure out the fudge factor from the chart to figure out in between sizes.
    BUT not all 2.00, 2.125, or 2.25 (or any width) tires are the same actual diameter, especially when you factor in operating air pressure and load on the tire. The ONLY accurate way to calibrate the computer is by doing a rollout.
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