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    Yen
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    Tire size for new cyclocomputer

    Another newbie question....

    I bought a cyclocomputer today to keep track of my distance and time on my new bike.

    The instructions explain how to change the tire size in the odometer function. The default setting on the computer was 820. I have 700x40c tires on my bike. The side of the tire says "42 - 622 (700 x 40c)". How does all that correlate with the default setting on the computer? I can raise or lower that number..... but to what?

    Jen
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    Ride Daddy Ride Jet Travis's Avatar
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    Do the instructions show settings for different tire sizes? If so is there one for 700 x 40? That would be the one to use. They may also have instructions for rolling the tire (on the bike) and marking the distance of one full revolution, then setting up your computer based on the distance. Worst case, you can do what I do in times of mechanical stress--go to the lbs when its not too busy and ask for help.
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    Yen
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    No, the instructions just say how to set the tire size on the computer, nothing about how to determine tire size. I may try rolling the bike one revolution.

    Thanks,
    Jen
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    I need more cowbell. Digital Gee's Avatar
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    Quote Originally Posted by Yen
    No, the instructions just say how to set the tire size on the computer, nothing about how to determine tire size. I may try rolling the bike one revolution.

    Thanks,
    Jen
    I can't answer your question, but I am impressed you can read the "manual" that came with the gadget. I'm guessing it's one large sheet of paper that's folded in half six times, and has the instructions printed in half a dozen languages, in 6 pt. font.
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  5. #5
    Senior Member Bill Kapaun's Avatar
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    Go to this link-
    http://sheldonbrown.com/cyclecomp_a.html

    Multiply by 10 should get you close. It appears the computer default is a 26X 2.125 tire.

    When you have a chance to actually ride a precisely mesured distance, you can "tweek" the numbers then.

    PS- Tires tend to run a bit smaller than their "listed" size, so you might want to use a slightly smaller number, like about 3% smaller.

    Edit- I forgot which forum this was. Are you old enough

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    Yen
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    Quote Originally Posted by Digital Gee
    I can't answer your question, but I am impressed you can read the "manual" that came with the gadget. I'm guessing it's one large sheet of paper that's folded in half six times, and has the instructions printed in half a dozen languages, in 6 pt. font.
    Actually, it's printed in ONE DOZEN languages. It was fun hunting for the English section. Thank God for bifocals!!

    Bill - thanks, I'll try that. (Old enough for what?)
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    Quote Originally Posted by Yen
    No, the instructions just say how to set the tire size on the computer, nothing about how to determine tire size. I may try rolling the bike one revolution.

    Thanks,
    Jen
    If you do a rollout, be sure your tires are inflated to the pressure you normally ride. Do the rollout while you are on the bike with someone holding you up but not pushing down on the bike. If you measure this distance in cm, I'm guessing there will be a way to enter that number.

  8. #8
    Senior Member Bill Kapaun's Avatar
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    I figured out the "code".
    Tire diameter in inches * PI (3.1416)

    Your tire- 40mm
    622MM (rim)
    622+40+40
    =702mm (Diameter of the tire)
    1mm = .03937"
    702*.03937= 27.638"
    27.638" * Pi (3.1416) =86.8"
    *10 = 868

    868 is the "magic number for you!

    It appears since your tires are listed as 42 AND 40 MM, 40 would probably be the number to use in your initial calculations. (to allow for the slightly smaller actual size)

    Since this is the 50+ forumn, I had to make sure you're "old enough"

    I've BEEN wearing bifocals for 49 years!!!

  9. #9
    Senior Member Old School's Avatar
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    Quote Originally Posted by Louis
    If you do a rollout, be sure your tires are inflated to the pressure you normally ride. Do the rollout while you are on the bike with someone holding you up but not pushing down on the bike. If you measure this distance in cm, I'm guessing there will be a way to enter that number.
    Use this method only if you are truly committed to "Fred" level accuracy!
    Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW! WHAT A RIDE!"

  10. #10
    Senior Member Old School's Avatar
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    Quote Originally Posted by Bill Kapaun
    I figured out the "code".
    Tire diameter in inches * PI (3.1416)

    Your tire- 40mm
    622MM (rim)
    622+40+40
    =702mm (Diameter of the tire)
    1mm = .03937"
    702*.03937= 27.638"
    27.638" * Pi (3.1416) =86.8"
    *10 = 868

    868 is the "magic number for you!

    It appears since your tires are listed as 42 AND 40 MM, 40 would probably be the number to use in your initial calculations. (to allow for the slightly smaller actual size)

    Since this is the 50+ forumn, I had to make sure you're "old enough"

    I've BEEN wearing bifocals for 49 years!!!
    I knew one of our 50+ forum members would have a 128-key calculator, horn-rimmed glasses, and a pocket protector!
    Life is not a journey to the grave with the intention of arriving safely in a pretty and well-preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW! WHAT A RIDE!"

  11. #11
    Yen
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    LOL!! I'm beginning to look forward to the hilarious responses in this forum.

    Thanks everyone!

    I'm off to a little league game so I will take another look at this later.... my head is spinning with numbers right now. It's drizzling this morning so no riding today unless it clears up later then I'll test the accuracy of the computer.

    Thanks again everyone.

    Jen
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    Senior Member CrossChain's Avatar
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    Strange, often the directions will offer a handy, generic chart of tire sizes that allows you to eyeball a good approximation. Jen, unless you are a compulsive, pocket protector type....a close guess is good enough. Speed is relative to your own performance and soon you'll discover what is fast for you, easy for you, typical for you...and you won't be checking the computer so much. As for distance, unless you ride huge mileage, the difference between a "good guess" and "precise accuracy" isn't so significant.

    Besides, wouldn't want your new-found joy in riding to descend into bean-counting compulsion (i.e. "If I sprint thru that red light I can keep my avg. speed up.")

  13. #13
    Time for a change. stapfam's Avatar
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    The mechanical side of biking is bad enough- but electronics get me every time. Now just a tip- Get yourself another magnet for the wheel- Then when you decide that you only want a quick 30 miler this morning- fit 2 magnets to the wheel. The 30 miles will fly past.
    How long was I in the army? Five foot seven.


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    Senior Member freeranger's Avatar
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    Use the roll out method and multiply the inches traveled by 25.4. That's your number.

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    Quote Originally Posted by Old School
    Use this method only if you are truly committed to "Fred" level accuracy!
    Fred level accuracy? Hrumph! I'll put my roll out calibrated bike computers up against any other method. Any day.
    Last edited by Louis; 04-07-07 at 03:32 PM.

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    Quote Originally Posted by freeranger
    Use the roll out method and multiply the inches traveled by 25.4 That's your number.
    +1 to the above EXCEPT, this would be off by a factor of 10 on my Cateye computers, and much more if your computer is in inches (83 x 25.4= 2108). I have Cateye Enduro 8's on three of my bikes so I am always resetting something. These three bike computers use a setting equivalent to the rolling circumference measured in centimeters.

    I think Yen's computer is set in units equal to 1/10th of an inch. Then again, maybe it is set to use inches with mph and centimeters with km/hour. (1 inch = 2.54 centimeters)

    You guys are working this too hard. You can calculate circumference with diamters and pie, or pigh, or pi, but Bill Kaupan above has it right.

    Yen, your tire is a 700 x 40. The instructions should list a setting for this tire. If they do not, go to a smooth floor, set the inflation valve on the bottom, and mark the spot. Roll it one revolution in a smooth straight line. Measure the distance on the floor in inches and convert to centimeters (cm) by multiplying time 2.54. That is the most accurate way to set the computer, using the actual rolling cirucmferenc. A 700 tire is about 83 0r 84 inches around, which would make a setting of 210 cm to 213 cm. Cateye lists a circumference of 220 CM for a "standard" 700x40 bike tire, so your circumference should be about 86.6 inches.

    But you have a default setting of 820? It might mean 82.0 inches. Maybe your computer uses 1/10th of an inch as the calibration, in which case 820 = 82 inches = 209.92 centimeters (go ahead and call it 210) which is also "standard" circumference listed by Cateye for a 26" x 1.5" tire, a mountain bike size.

    The hardest part is finding your own language on the little folded up manual, and then finding it again when you need. Why do I buy the same computer? So I can have extra copies of the little folded up instructions.
    Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman

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    All my computers will take a rollout reading in centimeters directly entered into the computer. No need for higher mathematics.

    Rollout is the best method to calibrate any bicycle computer. Period.

    Let's see now, Who are we going to listen to when it comes to bicycles? How 'bout Sheldon Brown? Yeah, that's the ticket. http://sheldonbrown.com/cyclecompute...n.html#rollout

    Fred level accuracy...my ass!

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    Quote Originally Posted by Louis
    Fred level accuracy? Hrumph! I'll put my roll out calibrated bike computers up against any other method. Any day.
    +1
    Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman

  19. #19
    Senior Member Bill Kapaun's Avatar
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    I knew one of our 50+ forum members would have a 128-key calculator, horn-rimmed glasses, and a pocket protector!

    None of the above!

  20. #20
    Yen
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    Quote Originally Posted by Monoborracho
    +1 to the above EXCEPT, this would be off by a factor of 10 on my Cateye computers, and much more if your computer is in inches (83 x 25.4= 2108). I have Cateye Enduro 8's on three of my bikes so I am always resetting something. These three bike computers use a setting equivalent to the rolling circumference measured in centimeters.

    I think Yen's computer is set in units equal to 1/10th of an inch. Then again, maybe it is set to use inches with mph and centimeters with km/hour. (1 inch = 2.54 centimeters)

    You guys are working this too hard. You can calculate circumference with diamters and pie, or pigh, or pi, but Bill Kaupan above has it right.

    Yen, your tire is a 700 x 40. The instructions should list a setting for this tire. If they do not, go to a smooth floor, set the inflation valve on the bottom, and mark the spot. Roll it one revolution in a smooth straight line. Measure the distance on the floor in inches and convert to centimeters (cm) by multiplying time 2.54. That is the most accurate way to set the computer, using the actual rolling cirucmferenc. A 700 tire is about 83 0r 84 inches around, which would make a setting of 210 cm to 213 cm. Cateye lists a circumference of 220 CM for a "standard" 700x40 bike tire, so your circumference should be about 86.6 inches.

    But you have a default setting of 820? It might mean 82.0 inches. Maybe your computer uses 1/10th of an inch as the calibration, in which case 820 = 82 inches = 209.92 centimeters (go ahead and call it 210) which is also "standard" circumference listed by Cateye for a 26" x 1.5" tire, a mountain bike size.

    The hardest part is finding your own language on the little folded up manual, and then finding it again when you need. Why do I buy the same computer? So I can have extra copies of the little folded up instructions.
    Monoborracho, I have the Cateye Enduro 8 (what an unbelievable coincidence... or is it a very popular calculator for the price point?). You offered the simplest method (why didn't I think of that??) to measure the distance traveled by one revolution of the tire. I will try it later.

    Since you have 3 of this particular calculator, how do you like it? Anything I should know about it?

    Thanks so much to EVERYONE. This has been a very enlightening -- and entertaining -- thread.

    Jen
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    Senior Member Terrierman's Avatar
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    I just reset my Cateye Micro Wireless last night to the Coda. 700x28's. I have the instructions, and the figure I had to enter for that tire size for that computer was 2136. The scale is in millimeters. The table lists 2200 mm for a 700x40. At least that's what the paperwork says. I have no idea what the scale might be for Cateye Enduro 8.
    It's all downhill from here. Except the parts that are uphill.

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    The 820, I'm guessing, is the circumference of the tire in inches multiplied by 10: 82 inches would be 6.83 feet or 2117mm, which is about the size of a 26-inch (diameter, as in a mountain bike) tire (most computers, at least all of mine, are set in millimeters, but it doesn't really matter). Just roll the thing out as somebody else has described, measure it in inches, multiply by 10 and use that as the setting.

  23. #23
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    Quote Originally Posted by Yen
    Monoborracho, I have the Cateye Enduro 8 (what an unbelievable coincidence... or is it a very popular calculator for the price point?). You offered the simplest method (why didn't I think of that??) to measure the distance traveled by one revolution of the tire. I will try it later.

    Since you have 3 of this particular calculator, how do you like it? Anything I should know about it?

    Thanks so much to EVERYONE. This has been a very enlightening -- and entertaining -- thread.

    Jen
    #1 - set it to AT (where it runs when you go) and leave it.

    #2 - forget about using it on more than one set of wheels.

    Its cheap, easy to use, and easy to reset.
    Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman

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    [QUOTE=Bill Kapaun]I knew one of our 50+ forum members would have a 128-key calculator, horn-rimmed glasses, and a pocket protector!QUOTE]


    Are you talking to me?

    You talking to me?

    You talking to me?

    Well, no pocket protector or horned rim glasses, but I have several calculators with a lot of buttons...one for scientific and one for financials. [ My slide rule is in a framed display box over my desk at home, but yeah, I know what all the numbers are for]
    Most economic fallacies derive from the tendency to assume that there is a fixed pie, that one party can gain only at the expense of another.....Milton Friedman

  25. #25
    Senior Member Dchiefransom's Avatar
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    I put a piece of tape on the side of the tire for a rollout. I put the bike next to the garage or other long area next to a support where I can hold myself up, with the tape down. I mark the pavement, sit on the bike and move forward until the tape is down again, and mark that. Measure with a tape measure, use an online conversion site to get my units, and set my computer. My Enduro 8 used millimeters.
    Silver Eagle Pilot

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