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  1. #1
    brad3104
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    Programming computer...

    Just got a Cateye velo 5. Nice basic computer. Its all set up...but i have 2 questions. One where should the sensor be on the spoke? The pictures look like about 3/4 of the way up the spoke...closest to the wheel. Is this correct?

    also my tire size is not on the chart....and the chart seems fishy.

    Cateye chart says....
    47-406 20x1.75=152cm
    47-406 20x1-3/8=162cm

    Mine is a 37-406 20x1.35=And it came out to exactly 150.5 cm when i measured it myeslf. How come my tire width is the smalles out of these but has the smallest circumference. The smallest out of the 2 listed above.....has the BIGGEST circumference. Does it have to do with the model or brand of the tire? note mine is a 37-406...whatever that means.

    For my first ride i just used the standard "20 inch" setting. However i got home and entered as close to the exact amount as possible. I entered 150 cm...as there is no room for decimals. Should i stick with the 150 cm that i input?

  2. #2
    Insane Bicycle Mechanic Jeff Wills's Avatar
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    Quote Originally Posted by brad3104 View Post
    Just got a Cateye velo 5. Nice basic computer. Its all set up...but i have 2 questions. One where should the sensor be on the spoke? The pictures look like about 3/4 of the way up the spoke...closest to the wheel. Is this correct?

    also my tire size is not on the chart....and the chart seems fishy.

    47-406 20x1.75=152cm
    47-406 20x1-3/8=162cm

    Mine is a 37-406 20x1.35=And it came out to exactly 150.5 cm. How come my tire width is the smalles out of these but has the smallest circumference. The smallest out of the 2 listed above.....has the BIGGEST circumference. Does it have to do with the model or brand of the tire? note mine is a 37-406...whatever that means.
    For my first ride i just used the standard "20 inch" setting. However i got home and entered as close to the exact amount as possible. I entered 150 cm...as there is no room for decimals. Should i stick with the 150 cm that i input
    ?
    37-406 means it's 37mm wide and fits a 406mm bead seat diameter rim. These are the ETRTO numbers, which are less ambiguous than older measurements. Here's some good reading if you're an insomniac: http://www.sheldonbrown.com/tire_sizing.html

    The chart is definitely weird. I think there's a typo- a 20 x 1 3/8" tire should be a 37-451 ETRTO size. It's the larger of the 2 20" tire size "standards" out there.

    The Sheldon Brown/Harris Cyclery site is a wealth of bicycle information, both useful and useless. Here's some reference material on cyclocomputers: http://www.sheldonbrown.com/cyclecomputers/index.html
    Jeff Wills

    All my bikes.

  3. #3
    brad3104
    Guest
    Instead of using the standard 20 inch setting on the computer...do u think i should go with the 150 cm manually inputed in?

  4. #4
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    Put a piece of tape on a part of tire. Start on a line with the tape on the floor, roll the wheel forward until the tape hits the ground again. Measure the distance between the two lines, put that in your computer. All it's trying to determine is the outside circumference of the tire so it knows how many times it has rotated per time elapsed.

    The position of the spoke magnet is completely irrelevant, like previously stated it just needs to know how many times the wheel has rotated per second to multiply that times the circumference of the wheel to find out speed and distance.

  5. #5
    brad3104
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    In my OP i said i measured the tire and it was 150.5 cm. I was just pointing out the Cateyes table of data seems fishy. So yes ill either enter 150 or 151.

  6. #6
    Senior Member BlazingPedals's Avatar
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    Pay no attention whatsoever to the numbers in the manual. The only thing they're good for is to verify that the numbers you come up with via roll-out are in the ballpark. If you measured 150.5, then enter 150. That'll get you within 0.3% accuracy, which is probably close enough for guv'ment work.

    My method of roll-out is to line up the valve stem with a crack in the pavement. With weight on the bike, roll the bike 3 revolutions of the tire and mark the spot where the valve stem lines up. Measure with a tape measure. Divide by 3 to get the average circumference, then multiply inches times 25.4 to get mm.

  7. #7
    rebmeM roineS JanMM's Avatar
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    The 20 x 1.35 Primo Comet Kevlar on my front wheel rolls out at about 150cm. Actually, it rolls out at a bit less than 59" cause there are very few metric tape measures to be had in the American Heartland.
    RANS V3 (steel), RANS V-Rex, RANS Screamer

  8. #8
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    That'll learn me to half read a post whilst mostly asleep

    Sorry for over explaining where it was unnecessary

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