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  1. #1
    Banned.
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    More information about # of skidding spots with gearing...


  2. #2
    Iguana Subsystem dolface's Avatar
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    that rocked! hooray for math-geek cyclists!

  3. #3
    nothing: lasts forever ink1373's Avatar
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    43 teeth here i come!

  4. #4
    Senior Member TimArchy's Avatar
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    that page seems to make it a lot more complex than it needs to be.

    48/16 = 3/1 = 3
    so the back wheel goes around three times with each crank rotation and ends up in the same place. so if you always skid with the same foot forward, you always hit the same spot. this is true for all ratios that are whole numbers.

    45/18 = 5/2 = 2.5
    now the crank has to go around two times to get the rear wheel back in the same position so you have two places on the wheel.

    48/15 = 16/5 = 3.2
    here, the crank has to go around 5 times to get back to the same spot on the rear wheel so you've got 5 spots to hit.

    48/17 = something with a lot of decimals.
    it won't reduce so the crank has to go around 17 times to hit the same place on the rear wheel.

    easy formula:
    reduce your ratio to the smallest denominator (chainring/cog). the denominator will tell you how many places you will skid on the rear wheel. (if you skid with either foot forward, double the number)

    much easier right?

    a month ago I taught a lesson to a 6th grade math class about ratios using my fix.

    tim
    Quote Originally Posted by Josh Frank
    I will derive power from their cries of despair. My crank a speedy dervish, spinning and spinning through the darkest night that anyone with the audacity to try and suck my wheel will ever see...

  5. #5
    72 & Sunny adamkell's Avatar
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    nice use of applied math with the kiddies

  6. #6
    Senior Member TimArchy's Avatar
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    yeah, my mentor teacher liked it a lot. I'm teaching high school geometry and algebra next spring. I'm trying to think of lessons using cycling that I can use on them.

    tim
    Quote Originally Posted by Josh Frank
    I will derive power from their cries of despair. My crank a speedy dervish, spinning and spinning through the darkest night that anyone with the audacity to try and suck my wheel will ever see...

  7. #7
    無くなった HereNT's Avatar
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    44/14 = 3.1428571428571428571428571428571 - dammit - I almost had the fabled pi gearing!!!!

    According to the last paragraph, taking the highest denominator (2) I have 7 patches to skid on...

    I don't see how he connects Sheldon with brakeless though...

  8. #8
    Iguana Subsystem dolface's Avatar
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    HereNT, he doesn't connect scheldon with brakeless;

    <snip>
    Though Sheldon Brown, the laws of several states and plain old common sense urge otherwise, many fixed gear riders choose to pilot their machines without brakes.
    </snip>

  9. #9
    無くなった HereNT's Avatar
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    Dang, losing that contact lens earlier must be affecting my eyesight or something. Found it again, but everythings kind of blurry out of that eye...

  10. #10
    Direct Hit Not Required BlastRadius's Avatar
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    I'm glad I found that elusive 43 tooth 118bcd chainring on Ebay.

  11. #11
    Senior Member TimArchy's Avatar
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    damn...
    this thread's been Pi-jacked
    Quote Originally Posted by Josh Frank
    I will derive power from their cries of despair. My crank a speedy dervish, spinning and spinning through the darkest night that anyone with the audacity to try and suck my wheel will ever see...

  12. #12
    BxTS gh-ap's Avatar
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    what's 52-17, for a math ******?

  13. #13
    Iguana Subsystem dolface's Avatar
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    you've got 17 patches, since 17 is a prime number.

  14. #14
    BxTS gh-ap's Avatar
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    hooray!

  15. #15
    as you wish, skeletor. ephemeralskin's Avatar
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    yup i think trevor worked all this out for us a while back. totally awesome.

    and now as of last week my new chainring is 43t. i also changed to a 3/32" drivetrain. hopefully ill take some pics in a week or so..

    'Fun means something that makes you feel good. Someone who likes movies might watch a movie for fun. Games are also a way to have fun. Most people like to have fun. [citation needed]' -simple.wikipedia.

    ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

  16. #16
    NACCC 2007 Winner
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    Quote Originally Posted by BostonFixed
    Fan-diddely-tastic. Now i'm gonna translate this into my native language and put it in our magazine and pretend that i figured it out myself

  17. #17
    natural born loser
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    *drool*

  18. #18
    Senior Member TimArchy's Avatar
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    Quote Originally Posted by dolface
    you've got 17 patches, since 17 is a prime number.
    it wouldn't matter if 17 was a prime number. if you ran a 51/17, you'd only have one skid patch since 51/17 = 3/1 = 3. whole number = one skid patch.

    52/17 indeed gives 17 skid patches, but it's because 52 and 17 are mutually prime.

    tim
    Quote Originally Posted by Josh Frank
    I will derive power from their cries of despair. My crank a speedy dervish, spinning and spinning through the darkest night that anyone with the audacity to try and suck my wheel will ever see...

  19. #19
    Retrogrouch in Training bostontrevor's Avatar
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    relatively prime.

    edit: hey, lookit that, indeed "mutually prime" is also an acceptable term. I don't think I've ever heard it called thaht.

  20. #20
    Iguana Subsystem dolface's Avatar
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    heh heh, i was gonna point that out too, nice to know that both are correct.

    btw, TimArchy, thanks for correcting my comment. nice catch

  21. #21
    Senior Member TimArchy's Avatar
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    mutually prime, relatively prime...
    I can't remember which is correct.
    I took abstract algebra twice, but it was two years ago
    I figured that since they were prime relative to each other...

    tim
    Quote Originally Posted by Josh Frank
    I will derive power from their cries of despair. My crank a speedy dervish, spinning and spinning through the darkest night that anyone with the audacity to try and suck my wheel will ever see...

  22. #22
    Direct Hit Not Required BlastRadius's Avatar
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    A prime chainring is what you want. Otherwise you'll need to do the calculation at the bottom.

  23. #23
    Iguana Subsystem dolface's Avatar
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    you don't need a prime chainring OR cog as long as they're prime relative to each other

  24. #24
    Direct Hit Not Required BlastRadius's Avatar
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    Yes, but what is most flexible is a prime chainring. Then you can run pretty much any size cog and not have to worry.

  25. #25
    troglodyte ryan_c's Avatar
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    Quote Originally Posted by BlastRadius
    Yes, but what is most flexible is a prime chainring. Then you can run pretty much any size cog and not have to worry.
    For anyone wondering, the prime chainrings of reasonable size would be 41, 43, 47, 53.
    Justification of reasonable size: 37 seems a bit small, 61 a bit big. Certainly a good spread though.

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