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  1. #1
    jrm
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    chainline impact on effort?

    I have a kona jts cross bike. I have it set up with a truvativ MTB crankset using a 113mm BB spindle. This is hooked up to a sram 8 spd 11-28 using a pc55 sram chain.

    When im in a 44T-14/15/16 combo i have between a 1.25 and 2" gap between the crankset and the cassette. How much does this 1 to 2 inch lateral gap my effort to turn over the cranks. The reason i ask is that if i shift down to the 32 and use the 11/12 or 13T cogs on the cassette the drivetrains seems so much smoother.

  2. #2
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    The drivetrain efficiency charts I've studied indicate an interesting trend:

    (1) For any given chainring you are operating in, drivetrain efficiency steadily drops off as the chain is shifted to smaller cogs on the cassette, even if the shift results in an optimized chainline.

    (2) Operating from a larger chainring and smaller cog is more efficient than operating from a smaller chainring and larger cog (assuming similar gear ratios).

    This would mean that running 44x16 is more efficient than 32x11, even though they both result in approximately the same gear ratio.

  3. #3
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    switch to 108 BB

    Quote Originally Posted by jrm
    I have a kona jts cross bike. I have it set up with a truvativ MTB crankset using a 113mm BB spindle. This is hooked up to a sram 8 spd 11-28 using a pc55 sram chain.

    When im in a 44T-14/15/16 combo i have between a 1.25 and 2" gap between the crankset and the cassette. How much does this 1 to 2 inch lateral gap my effort to turn over the cranks. The reason i ask is that if i shift down to the 32 and use the 11/12 or 13T cogs on the cassette the drivetrains seems so much smoother.
    If your cross frame has road (130 mm) dropout spacing you might want to switch to a 108mm spaced BB. Look to see how much clearance you have at the chainstays and how much room the front derailleur has to move inboard. Anytime you ride with a big chain offset you lose efficiency but even more problematic is the increased risk of chainsuck and increased drivetrain wear.

  4. #4
    jrm
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    Funny you should say that...

    Quote Originally Posted by barrows
    If your cross frame has road (130 mm) dropout spacing you might want to switch to a 108mm spaced BB. Look to see how much clearance you have at the chainstays and how much room the front derailleur has to move inboard. Anytime you ride with a big chain offset you lose efficiency but even more problematic is the increased risk of chainsuck and increased drivetrain wear.
    I ordered a 108bb from Cambria 2 weeks ago and they totally dropped the focking ball. Im still waiting.

    I asked about triple to double conversion on roadbike review and someone said that was the thing to do. If i everget my BB im hopingthat this will no longer be an issue.

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