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  1. #1
    we are 138 Philatio's Avatar
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    Changing chain ring size, keep same gear inches

    If you took two set ups, both with similar gear inches but dramatically different chain ring sizes, would there be any sort of noticable difference in mechanical advantage? Would it "feel" easier to spin with one or the other?

    For sake of argument something like 39/14 and 52/19, both giving ~74 gear inches.

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    52/19 should feel "smoother", but not really easier to pedal. This has to do with the way more teeth are engaged on the cog/chainring at any given time as opposed to 39/14. It's kinda hard to explain, but the more teeth engaged at any one time should make things feel smoother.

    Obviously, 52/19 will also be heavier, and 19 teeth cogs may limit you to only a couple manufacturers.

  3. #3
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    I use to run 39x15 and now run 49x19. They are basically both ~69 gear inches. The main difference I notice is that my new setup is quieter. Not necessarely because of the size difference, though. It's also 1/8", so different cog/chainring/chain. Who knows where the quietness came from.

  4. #4
    \||||||/ ZachS's Avatar
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    bigger chainrings and cogs also look cooler

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    Senior Member barba's Avatar
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    Is there any difference in wear based on the gear and ring sizes? Logic would seem to imply that more teeth would distribute the load across more contact points.

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    With bigger cog/chainring for the same ratio:

    Less drivetrain wear, as torque is spread over larger area
    More efficient, less chain deflection=less heat

    Why anyone would run small chainring/sprocket out of choice rather than necessity, who knows?

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    Quote Originally Posted by highlyselassie
    With bigger cog/chainring for the same ratio:

    Less drivetrain wear, as torque is spread over larger area
    More efficient, less chain deflection=less heat

    Why anyone would run small chainring/sprocket out of choice rather than necessity, who knows?
    i understand why those would be true in theory, but in practice i doubt either of them have any effect.

  8. #8
    not the car. tempo's Avatar
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    in my observations....

    more teeth in contact = more *connected*, and easier to hold pace...think truckin'

    less teeth in contact= starts quicker, and better in sprints but not for distance

  9. #9
    "not enough rage" Old Breadbutt's Avatar
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    Quote Originally Posted by highlyselassie
    Why anyone would run small chainring/sprocket out of choice rather than necessity, who knows?
    weight would seem the obvious reason, but resistance probably has more impact.

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    With a bigger ring, you get to roll that one pants leg up more.
    Bigger looks better, but unless you are comparing the same brand of rings, chain, and cogs in the same condition at time of install, there are a lot of other variables to consider. You may have a more round or true chainring.

  11. #11
    "not enough rage" Old Breadbutt's Avatar
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    Quote Originally Posted by highlyselassie
    Why anyone would run small chainring/sprocket out of choice rather than necessity, who knows?
    weight would seem the obvious reason, but resistance probably has more impact. I have some friends that ride SS mountain and BMX, one of them said that they keep it small so that it doesn't catch on logs and ****.

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    Quote Originally Posted by zip22
    i understand why those would be true in theory, but in practice i doubt either of them have any effect.
    They'd be true in practice too, it's just pure Vulcan logic.

    It's our legs driving these things, so even small efficiency gains should be embraced with open arms. Of even more interest, the extra longevity of such a setup would far outweigh any *supposed* advantages by losing 100/150g, if that on chainring/sprocket.

    Try it with two bikes if you like, same gear ratio, 14 tooth sprocket on one, big as you can go on the other(20/21?, obviously chainring clearance is going to be the determining factor). Since efficiency is such a grey area for those of us without access to a laboratory, just note the chain/chainring/sprocket wear over time.

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    Something I'd love to see tried out is 80+ teeth chainrings with 22+ teeth sprockets in the rear on track bikes. I'd bet good money that even if these setups weighed 300/400g more than other bikes on the track, given similar riders/or the same rider on timed laps, the added efficiency would decrease times.

    Anyone game?

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    its funny how miniscule advantages in wear and efficiency are embraced with open arms but *supposed* weight advantages are shrugged off.

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    Senior Member barba's Avatar
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    Quote Originally Posted by highlyselassie
    Something I'd love to see tried out is 80+ teeth chainrings with 22+ teeth sprockets in the rear on track bikes. I'd bet good money that even if these setups weighed 300/400g more than other bikes on the track, given similar riders/or the same rider on timed laps, the added efficiency would decrease times.

    Anyone game?
    I have an old Campy 57t ring and it looks huge. I can't even imagine what 80 mould look like.

  16. #16
    don't pedal backwards... MacG's Avatar
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    Quote Originally Posted by barba
    I have an old Campy 57t ring and it looks huge. I can't even imagine what 80 mould look like.
    Maybe like this?



    (from here)
    from Minneapolis, with bike love

  17. #17
    \||||||/ ZachS's Avatar
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    Quote Originally Posted by highlyselassie
    Something I'd love to see tried out is 80+ teeth chainrings with 22+ teeth sprockets in the rear on track bikes. I'd bet good money that even if these setups weighed 300/400g more than other bikes on the track, given similar riders/or the same rider on timed laps, the added efficiency would decrease times.

    Anyone game?
    if it did, racers would already be doing it.

    and if you want to bet your good money against mine, you'd be more than welcome. any possible advantage the "added efficiency" would add (i.e. not much, if any) would be more than offset by reduced aerodynamics.

  18. #18
    Senior Member mattface's Avatar
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    I don't know about any perceivable difference in mechanical advantage, but the increased wear especially on smaller cogs is significant. Even though the chain may wrap around more than half the cog, I believe I read somewhere that the leading 1/4 of the cog bears the force. So when you have a 12 tooth cog, that's 3 teeth dividing whatever torque you are applying. That WILL wear cogs significantly faster than it would on a larger cog, and that's why on super lightweight aluminum cassettes the small cogs are made from Steel or titanium.

    I would think larger rings and cogs would have more friction which would balance out any mechanical advantage, and the that improved wear characteristics would reach a point of diminishing returns LONG before you got to 80 tooth chainrings. For instance the difference between a 12 tooth and 16 tooth is one more tooth engaged, but when you only had 3, that one more means 1/3 less force per tooth. now jump from 16-20, and the one more tooth is only 1/4 less force. To get another full tooth engaged on the rear, you'd next need to jump to a 24 tooth cog, and you'd only reduce wear by 1/5. At least that's how I see it. I tend to think 16 teeth is probably the sweet spot for weight/wear characteristics, but there's no high end engineering going on here just my mind working through the mechanics. Force ÷ teeth.


    For a more significant way to reduce chain and cog wear, always use even numbers of teeth as explained here by Sheldon Brown http://www.sheldonbrown.com/chain-life.html

    I wish I'd read that before settling on 46x17

  19. #19
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    I would really like to see some numbers on how much difference that even/even actually makes. It still sounds theoretical at best to me.

  20. #20
    i don't stop travsi's Avatar
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    Quote Originally Posted by zip22
    its funny how miniscule advantages in wear and efficiency are embraced with open arms but *supposed* weight advantages are shrugged off.
    that's because on the track weight doesn't
    play as much of a roll as efficiency.

    and as far as the efficiency goes the smaller ratios
    do give an advantage in sprint situations.

    does anyone know why the 10 pitch never caught on?
    i heard that it makes a difference, or is that just hearsay?

  21. #21
    don't pedal backwards... MacG's Avatar
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    Quote Originally Posted by travsi
    does anyone know why the 10 pitch never caught on?
    i heard that it makes a difference, or is that just hearsay?
    Is that the metric oddball chain that whoever tried to push a while back? If so, then the theoretical advantage is that it allows you to have more teeth engaged without having such physically large parts, so there would also be a little less weight. Other than that, I see no manner in which a smaller pitch chain could offer an advantage.
    from Minneapolis, with bike love

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