Gearing Opinions- Mtbr.com
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  1. #1
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    Gearing Opinions

    Does anyone have any sound background or knowledge on the benefit of running larger chain rings w/ larger cogs to produce relatively similar ratios (aside from chain wrap & wear).

    Example is there a clear benifit to running a 35x19 vs a 34x18?

    35x19 = 1.842
    34x18 = 1.889

    Note: the gearing in question is regarding 29er's.

    Thanks!

    P.S. single speed riding / racing has turned me into a ratio obsessed geek... one has got to wonder S.S.ing is really pedaling the simple life...lol!

  2. #2
    Stateline Falls, Watauga
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    Well, first of all those two gears are not "relatively similar." 35:19 is a significantly easier gear. 36:19 = 1.895 would be the next chainring up that's close to 34:18.

    Personally, I prefer smaller chainrings for better ground clearance. Others will say that larger rings == more teeth == less wear == longer life. Maybe so. Anyone who says there is a torque / mechanical advantage difference between two gears of the same ratio is smoking something good.
    Last edited by JeffL; 05-25-2012 at 12:48 PM.
    It never gets easier, you just go faster. -Greg LeMond
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  3. #3
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    Nevermind - I was looking for constructive feedback not a keyboard argument. Should have known better. Off to the woods.

  4. #4
    Gigantic Hawk
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    You answered your own question. The benefit of larger diameter rings and cogs is chain wrap. I'd rather have smaller rings and cogs, as JeffL stated, due to ground clearance. I also feel that a smaller diameter is less prone to flex, wrap, or distort.

    In the example that you give, the benefit of either combo is up to the rider. 35x19 would be my choice because it is closer to the 32x18 that I run. There is a pretty big gap between 35x19 and 34x18.
    Sheldon's calculator is a great tool for comparing gear ratios.
    Sheldon Brown's Bicycle Gear Calculator

  5. #5
    more skier than biker
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    as others stated, more overall teeth in the drivetrain = longer overall drivetrain life (less wear and tear). Not much, but a little.

    also, in my personal experience, running more teeth has a different "feel". Probably not much in the way of mechanical advantage, but I like the "feel" of a 36 tooth chainring vs. a 32 tooth. For example, given a 32x20 drivetrain and a 36x22 drivetrain (very similar, with the 36x22 slightly 'harder'), I much prefer the feel of the 36x22. This might be because the chain enters and leaves the cogs / chain rings at a mellower angle...not really sure.

    On most of my local trails, I don't need to be concerned with ground clearance, so don't mind running the larger chainrings. Others will feel differently if that's a concern.

    In the end, it's really no big deal either way. You'll adapt to either drivetrain scenario just fine.
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  6. #6
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    If you're running aluminum ring and cog, i would go larger for wear. If you're running stainless or ti, go smaller because its not going to wear as fast. You will decrease weight with the smaller settup and any cog with 16t or more is going to provide enough chainwrap as long as its settup correctly.

    If you're running a tensioner (especially pushing away) then a bigger settup would be best to get all the bite possible.

  7. #7
    (Ali)
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    Those two ratios are similar because the difference is 2%, which happens to be zero in mountain biking.

    Also, one tooth does not make any difference in ground clearance.

    Ali

  8. #8
    Stateline Falls, Watauga
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    Yeah, a half a tooth is zero in mountain biking. Especially in the singlespeed mountain biking forum, where no one ever worries about or obsesses over gearing. Ever.

    I tend to think about gear difference in terms of the number of teeth change at the rear cog, with the chainring size held constant. The difference between the two gears cited by the OP is 1/2 tooth at the cog. Yeah, zero
    Last edited by JeffL; 05-26-2012 at 03:50 AM.
    It never gets easier, you just go faster. -Greg LeMond
    I'm not as fast as I think I am. -JeffL

  9. #9
    Gigantic Hawk
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    A half tooth can end up being a big deal to some. It may mean not making that climb, or not catching somebody on that sprint.

  10. #10
    Oaktown Honkey on Strava
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    If you use a "half tooth", make sure you get a "half link", or chain will run weird.

  11. #11
    Gigantic Hawk
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    Quote Originally Posted by hoolie View Post
    If you use a "half tooth", make sure you get a "half link", or chain will run weird.
    Half links work with normal cogs. You half to get the ever elusive quarter link. The hardest thing about using them though is lining them up just right so that they engage the half tooth perfectly. And don't even get me started on proper half tooth orientation...

  12. #12
    local trails rider
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    To the original question... I don't see one or two teeth here or there being significant for wear or ground clearance. I like my SS chainrings to be around 32 to 36 tooth, choice depending on getting a good ratio with suitable chain length.

    "it IS possible that you are faster or slower than anybody else who is having at least as much if not more or less fun"

  13. #13
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    I have ridden my SS with a 32 and a 36 chainring and see no difference in performance. It is all about the ratio from front to back, as mentioned above. The Sheldon Brown page listed above is a great resource. I calculate using the "gear inches" and that breaks it down into something simple enough for my simple brain to understand.

    I am currently riding with the 36 and have picked up a 34, just for continued comparisons and to try something different. The 36 does hit sometimes on logs, etc, but I suspect that is more my poor ability rather than the size of the ring.

    Good luck. Part of what I like about MTB is playing around with this stuff. Just good fun.

    John
    On One Summer Season Single Speed

  14. #14
    Oaktown Honkey on Strava
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    All half link jokes aside,

    Problem with a big chain ring is clearance. On my NINER with EBB, hitting logs is a no no. I found out the hard way that riding my chainring over 2 ft tall logs CAN bump EBB out of position and loses chain. Thank god I was at the end of my ride, since way out there would have been misery. So, clearance IS an issue for me where I ride.

  15. #15
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    Quote Originally Posted by hoolie View Post
    Problem with a big chain ring is clearance. On my NINER with EBB, hitting logs is a no no. I found out the hard way that riding my chainring over 2 ft tall logs CAN bump EBB out of position and loses chain. Thank god I was at the end of my ride, since way out there would have been misery. So, clearance IS an issue for me where I ride.
    Granted, I stand corrected. Chain ring size is important depending on trails, obstacles etc. Thanks for the further perspective.

    John
    On One Summer Season Single Speed

  16. #16
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    There are other benefits to using larger chainrings and cogs. It is correct that the torque is equal with the same gear ratios, but the tension on the chain and the load on the teeth can vary a lot with different diameter cogs.
    Example:
    F = 50 lbs force at tire contact patch
    D = 27 tire diameter
    T = Torque = F*(D/2) = 675 in/lbs
    16T cog = 2.563 pitch diameter
    22T cog = 3.513 pitch diameter
    16T Chain tension = T/(PD/2) = 527 lbs
    22T Chain tension = T/(PD/2) = 384 lbs
    Now assuming the chain wraps around 180 degrees with equal load on each tooth
    16T tooth load = 527/8= 66 lbs force per tooth
    22T tooth load = 384/11= 35 lbs force per tooth
    So it is clear that a larger cog will put less load on the chain and cog which will make parts last longer and reduce breakage

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