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  1. #1
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    Cyclocross gear ratio question

    If 34/15 is similar in ratio to 42/18. What if any draw backs would there be to running a smaller chainring and cog. Are there measurable efficiency gains either way?

  2. #2
    Riding Engineer Tomo_Ishi's Avatar
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    I think you are better off with 42/18. I think 15T might be too small and chain might skip. Sheldon Brown said gears and chains are less strained with big gears (given same gear ratio), too. (Go to http://sheldonbrown.com/singlespeed.html and look for an entry under "Big or Small?"

    He also said clearance could become a problem, though. You should check in with Cyclocross forum to find out about the clearance you need.


  3. #3
    aka mattio queerpunk's Avatar
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    i too have heard from trackies that larger chainring/cog combinations are more efficient.

    i saw the title of the thread and was gonna chime in and say "i rode 42x18 for a few cross races and it was good."

    'course if you don't want to spend money on a new cog and cr, you could just do the 34 15 or whatever you've got.
    the hipster myth.

    i practice vagabondery.

  4. #4
    Ride for Life wearyourtruth's Avatar
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    the reason a smaller chainring/cog combo is beneficial for cyclocross is the clearance of the chainring. a cyclocross frame is already designed with a higher BB for this. it's simple... the smaller your chainring, the taller the obstacle you can roll over without trouble.

    it is true what has been said about chain wear though. a 15t will wear your chain out a little faster than an 18t.

    as for efficiency, it's pretty much identical.
    before posting, a "noob" should always ask themselves "could this have been answered by first visiting Sheldon Brown

    -Tim-
    www.velocipedebikeproject.org

  5. #5
    Team Beer Cynikal's Avatar
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    I run a 38x17 with is about the same. It's what I had in the parts bin and works. SS CX kick a$$.
    I'm not one for fawning over bicycles, but I do believe that our bikes communicate with us, and what this bike is saying is, "You're an idiot." BikeSnobNYC

  6. #6
    Senior Member mihlbach's Avatar
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    Quote Originally Posted by Tomo_Ishi View Post
    I think you are better off with 42/18. I think 15T might be too small and chain might skip.
    This is nonsense.


    Quote Originally Posted by wearyourtruth View Post
    the reason a smaller chainring/cog combo is beneficial for cyclocross is the clearance of the chainring. a cyclocross frame is already designed with a higher BB for this. it's simple... the smaller your chainring, the taller the obstacle you can roll over without trouble.

    it is true what has been said about chain wear though. a 15t will wear your chain out a little faster than an 18t.

    as for efficiency, it's pretty much identical.
    A+

  7. #7
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    Great info. I am going to run 34/15 see how things go. I'll report back with my opinions once cross season gets under way. Thans

  8. #8
    Dion Rides
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    Quote Originally Posted by mihlbach View Post
    This is nonsense.

    I think you can post this in every thread, on every board, on BF.

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