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  1. #1
    Al noisebeam's Avatar
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    Which cog/ring would you choose?

    These are all basically the same ratio:

    41x14
    43x15
    47x16
    49x17

    Al

  2. #2
    Slower than you Judah's Avatar
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    47x16, this gives you the option of going down to 47x20 or up to 47x13, a good range IMHO...

  3. #3
    heliocentrist cicadashell's Avatar
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    possible selection criteria:

    a) availability of parts
    2) number of skid patches
    iii) spreading out the wear

    i would pick the combination easiest to obtain - z.b. i have a 17-tooth cog already, all i need is the chainring (although of course cogs are less expensive than chainrings).

  4. #4
    Al noisebeam's Avatar
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    Quote Originally Posted by cicadashell
    possible selection criteria:

    a) availability of parts
    2) number of skid patches
    iii) spreading out the wear

    i would pick the combination easiest to obtain - z.b. i have a 17-tooth cog already, all i need is the chainring (although of course cogs are less expensive than chainrings).
    I picked 41, 43, 47, 49 because with the exception of 49x14 these four chainrings all result in the number of skid patches equal to the number of cog teeth (at least for cogs 12-18)
    I already have a 14 cog, but don't think it would be wise to go with a 41 chainring as it may be limiting.
    So I guess it boils down between 43 and 47 where I could get use out of the 14 with 43.

    I made this handy chart to help me figure out skid patches and equivalent ratios:


    Al

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    whichever cog/ring matches the ring/cog I already own.

  6. #6
    Senior Member etchr's Avatar
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    Quote Originally Posted by noisebeam
    I made this handy chart to help me figure out skid patches and equivalent ratios:
    sweet!
    love delights to give.

  7. #7
    i don't stop travsi's Avatar
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    just remember, big chainring = sexy

  8. #8
    broken spokes bike club napalmandroses's Avatar
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    that chart is amazing

    right click save!

  9. #9
    Lord Carlton of Worksop ETQC's Avatar
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    Quote Originally Posted by travsi
    just remember, big chainring = sexy
    Does this mean that I would have to change my 53/18 to a 54/18 to gain aditional sexiness with the ladies?
    Falling down is Newton's way of saying you suck.

  10. #10
    Senior Citizen Discount fixedfiend's Avatar
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    Quote Originally Posted by ETQC
    Does this mean that I would have to change my 53/18 to a 54/18 to gain aditional sexiness with the ladies?
    Actually bring your back cog down to 16 and your penis will grow

  11. #11
    Direct Hit Not Required BlastRadius's Avatar
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    Quote Originally Posted by Judah
    47x16, this gives you the option of going down to 47x20 or up to 47x13, a good range IMHO...
    Seconded.

  12. #12
    hang up your boots ostro's Avatar
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    also this is for one foot only, if you skid with different foot, you can double your spots

  13. #13
    Al noisebeam's Avatar
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    Quote Originally Posted by ostro
    also this is for one foot only, if you skid with different foot, you can double your spots
    Of course, but the chart still gives a comparision that is valid. Not to mention that one can spin tires on the rims - but the bottom line is that the higher number of skid spots the less you have to think about any of this.

    I'm leaning toward a 43 ring. Right now I converted an old bike resulting in 40x14, but for a variety of reasons I (unfortunately) need to change the cranks, so I'm using this as an opportunity to pick a good size chainring.

    I wonder why 48x16 is so oft recommended as it has the worst skid spot? I guess 48 chainrings are more common.

    Al

  14. #14
    heliocentrist cicadashell's Avatar
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    Quote Originally Posted by noisebeam
    I picked 41, 43, 47, 49 because with the exception of 49x14 these four chainrings all result in the number of skid patches equal to the number of cog teeth (at least for cogs 12-18).Al
    i noticed that; they are all prime. nice chart! i still listed skid patches as a possible criterion because some persons might feel that 17 is a lot more than 14 (or, for the ambidextrous, 34 is even greater than 28).

  15. #15
    Al noisebeam's Avatar
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    Quote Originally Posted by cicadashell
    i noticed that; they are all prime. nice chart! i still listed skid patches as a possible criterion because some persons might feel that 17 is a lot more than 14 (or, for the ambidextrous, 34 is even greater than 28).
    What do folks who primarily skid stop think is a good minimum of actual skid patches? I bolded everything above 7 (which woudl be 14 for ambi of course)

    Al

  16. #16
    hang up your boots ostro's Avatar
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    Quote Originally Posted by noisebeam

    I wonder why 48x16 is so oft recommended as it has the worst skid spot? I guess 48 chainrings are more common.

    Al
    I would say that someone is conspiring with tire companies to make that claim. I am in the same boat with 14x42

  17. #17
    Tiocfáidh ár Lá jfmckenna's Avatar
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    Quote Originally Posted by napalmandroses
    that chart is amazing

    right click save!
    yup

    good work noisebeam

  18. #18
    SuperstitiousHyperrealist jinx_removing's Avatar
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    It would be really cool to collect really interesting/helpful things like this and jimv's post and keep them somewhere. Every so often really good, well thought out posts appear and after the thread dies it takes me forever to find them. Well, I guess that's my own problem. But still it would be nice.

  19. #19
    ******** modmon's Avatar
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    Quote Originally Posted by jinx_removing
    It would be really cool to collect really interesting/helpful things like this and jimv's post and keep them somewhere. Every so often really good, well thought out posts appear and after the thread dies it takes me forever to find them. Well, I guess that's my own problem. But still it would be nice.
    seconded. this chart would fit nicely in a 'FAQ Sticky'.

  20. #20
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    Quote Originally Posted by ostro
    also this is for one foot only, if you skid with different foot, you can double your spots
    not always, though. one case that comes to mind is a 2:1 ratio - you have only 1 skid spot even if you skid both ways.

  21. #21
    Senior Member Kiecker's Avatar
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    yep. There's bound to be overlap between skidding with both feet.

  22. #22
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    umm, what's a skid patch?

  23. #23
    King of the Hipsters
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    All skidding aside, I have a mechanical intuition that larger chainring and sprocket pairs have lower stresses and greater efficiencies.
    I say intuition because I can't prove it with numbers.
    However, for a given ratio between front and rear, it seems that the smaller the number of teeth the less mechanically elegant the system.

    Secondly, how much of a rear tooth spread will one chain and horizontal dropouts support?
    If each tooth in the rear cog moves the axle one eighth of an inch forward, going from 13t to 21t involves one inch of travel (assuming 1/8" per tooth).
    Not that anyone would do that.
    Still, what tooth spread represents a reasonable spread, say on a fixed fixed hub that one wanted to flip over with the same chain?
    Does the size of the gear pairs matter in all of this?

    For myself, building my winter bike (with 38mm tires), a 43t chainring and 15t and 17t cog on a fixed fixed hub would serve me well, if it has the same mechanical efficiency as say a 49X17X19 combination, which has almost the same numerical ratios.
    And, by the way, the chainring and cog combinations above give me the same gear inches on a 38mm tire as I presently have on my 48X16X18 with 23mm tires.

  24. #24
    Iguana Subsystem dolface's Avatar
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    Quote Originally Posted by pista_chica
    umm, what's a skid patch?
    the place on your tire that's in contact with the ground when you're skidding.

  25. #25
    Retrogrouch in Training bostontrevor's Avatar
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    Quote Originally Posted by Ken Cox
    All skidding aside, I have a mechanical intuition that larger chainring and sprocket pairs have lower stresses and greater efficiencies. I say intuition because I can't prove it with numbers.
    I believe this has been experimentally demonstrated.

    Does the size of the gear pairs matter in all of this?
    Nope. Assume the ring is x teeth, one cog is y teeth, and the other is z teeth. The first gear ratio can be expressed as x/y and the second as x/z. To compare the second gear to the first, we would look at (x/y)/(x/z). Expand this to get xz/xy. The x's cancel out and we have z/y.

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