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  1. #1
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    Crank/BB only rough in certain gears???

    Hi, newb question, hoping someone here can point me in the right direction...

    I was riding today on a smooth, flat road and noticed that when in the middle ring, lowest gear (11t in rear) my cranks felt gritty. Shift up 3 or 4 gears and they felt smooth. I thought this was odd and was wondering if anyone could point me in the right direction. I don't know if it is worth mentioning that last week I had creaking in my rear cassette and it turned out that the cassette was a little loose. I figure it is a new bike and things loosen up as it is broken in, but do cranks really loosen? Oh, BTW the bike has only 170 miles total on it.

    The cranks and BB are Shimano SLX.

    Thanks.

  2. #2
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    When you use the middle ring and the outboard cogs, the chain may end up rubbing on the inner side of the big chainring as it passes. Could that be it? If so, just punch up to the big ring and then find the cog that feels good from there.

    The chain also might rub your front derailleur cage. If so, an adjustment will probably help. Your bike shop should be able to get that touched up quickly for you, or consult Park Tool's how-to section for some guidance.

  3. #3
    Bicyclochondriac.
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    Quote Originally Posted by sageashton
    Hi, newb question, hoping someone here can point me in the right direction...

    I was riding today on a smooth, flat road and noticed that when in the middle ring, lowest gear (11t in rear) my cranks felt gritty. Shift up 3 or 4 gears and they felt smooth. I thought this was odd and was wondering if anyone could point me in the right direction. I don't know if it is worth mentioning that last week I had creaking in my rear cassette and it turned out that the cassette was a little loose. I figure it is a new bike and things loosen up as it is broken in, but do cranks really loosen? Oh, BTW the bike has only 170 miles total on it.

    The cranks and BB are Shimano SLX.

    Thanks.
    I think it is very likely that it is the front derailleur that the chain is rubbing up against. If so, you need to tighten the FD cable a tad to pull the FD outboard.

  4. #4
    Nouveau Retrogrouch SuperModerator
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    Quote Originally Posted by sageashton
    Hi, newb question, hoping someone here can point me in the right direction...

    I was riding today on a smooth, flat road and noticed that when in the middle ring, lowest gear (11t in rear) my cranks felt gritty. Shift up 3 or 4 gears and they felt smooth. I thought this was odd and was wondering if anyone could point me in the right direction. I don't know if it is worth mentioning that last week I had creaking in my rear cassette and it turned out that the cassette was a little loose. I figure it is a new bike and things loosen up as it is broken in, but do cranks really loosen? Oh, BTW the bike has only 170 miles total on it.

    The cranks and BB are Shimano SLX.

    Thanks.
    Chain angle. The chain is angling quite a bit, which adds friction. Shift to the middle of the cassette and the chain runs straight from ring to cog, which is most efficient.
    mtbtires.com
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  5. #5
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    Quote Originally Posted by mechBgon
    When you use the middle ring and the outboard cogs, the chain may end up rubbing on the inner side of the big chainring as it passes. Could that be it? If so, just punch up to the big ring and then find the cog that feels good from there.

    The chain also might rub your front derailleur cage. If so, an adjustment will probably help. Your bike shop should be able to get that touched up quickly for you, or consult Park Tool's how-to section for some guidance.
    Sorry, I should have mentioned that I checked the front derailleur and it was clear - no rub. I will check for rub on the large chain ring tonight. Thanks.

  6. #6
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    Could also be that your 11 has serious wear, and the chain is shifting about to take up the wear. In this case it feels like the front as the movement is transferred through the chain to the cranks.
    Rimmer - "There's an old human saying - if you talk garbage, expect pain"

  7. #7
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    Quote Originally Posted by AlexRandall
    Could also be that your 11 has serious wear, and the chain is shifting about to take up the wear. In this case it feels like the front as the movement is transferred through the chain to the cranks.
    It is a brand new cassette, so that is not it. And I checked for rubbing of the chain on the middle chain ring, no dice.

    Does water get in BB easily? It has been raining out here in Cali and I have been riding through some streams, but I have never had water be a real issue on my older bikes.

  8. #8
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    Its not your BB or Crank. Its the excessive angle the chain has when in that combo. The best thing to do is if you need to use your 11t gear with the middle chain ring, is to upshift to the large chain ring and select a gear on the cassette that will feel similar to the middle chain ring/11t gear.

  9. #9
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    Water getting into the bearings could be part of the problem. Using the 11 would put more stress on your bb compared to a middle gear I think. If you don't feel the problem with your big ring then it's probably chainline, but hard to believe you could have a bad enough chainline with the middle ring.

  10. #10
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    At 170 miles The drive train should be broken in enough to be completely smooth cranking in all middle ring gears. It could be the shifter cable is slightly too tight. Turn the barrel adjuster inward 1/4 to 1/2 turn to shorten the housing. If no better, return the barrel adjuster to where you started from and take the bike to your dealer, they normally do the tune up for free, and check that everything is tight and aligned properly.

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