Changing cog size- Mtbr.com
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  1. #1
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    Changing cog size

    Wanting to move from a 32-20 to 32-18 setup. What will I need to do to the chain to allow the smaller cog? Any other considerations?
    Thanks

  2. #2
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    if you're stepping down, then you may be able to get away by just using your tensioner. If you're maxing on your your tensioner's range, then you'll need to take off a link. Can you give us more info on what bike, tensioner type etc.?

  3. #3
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    Quote Originally Posted by jammo View Post
    Wanting to move from a 32-20 to 32-18 setup. What will I need to do to the chain to allow the smaller cog? Any other considerations?
    Thanks
    I didn't do anything for my set up. I just swapped the 20t for an 18t, jumped on and rode.

  4. #4
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    The sliders on my Rockhopper take me from 32/20 to 32/17.

  5. #5
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    what frame do you have? if you have a lot of room to move the axle position, you might be able to take out a link. but if you do that and decide in the near future that you want your 20t back on there, you will need to somehow add a link to your chain or put a longer chain back on.

  6. #6
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    [QUOTE=goldenaustin;9846052]if you're stepping down, then you may be able to get away by just using your tensioner. If you're maxing on your your tensioner's range, then you'll need to take off a link. Can you give us more info on what bike, tensioner type etc.?[/QUOTE

    Trek Marlin SS. I don't have a chain tensioner, it's just built in to the frame with sliding bolts.
    Tensioner bolts are currently about halfway back on the 20T and there is some chain slap.

  7. #7
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    You may need a http://www.amazon.com/gp/aw/d/B001CN...948267-9376604 half-link.

    Sent from my Samsung Galaxy Note II

  8. #8
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    The frame is a Trek Marlin SS. I don't have a chain tensioner, it's just built in to the frame with sliding bolts.
    Tensioner bolts are currently about halfway back on the 20T and there is some chain slap.

  9. #9
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    Just try it, if it doesn't work, take a link out.

  10. #10
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    If it were me I would go with bigger ring and keep the 20 tooth cog because the system will run smoother. You could use a 35/20 because it is a very similar ratio to the 32/18. You will need to add some links or slide your wheel forward.

  11. #11
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    Quote Originally Posted by febikes View Post
    If it were me I would go with bigger ring and keep the 20 tooth cog because the system will run smoother. You could use a 35/20 because it is a very similar ratio to the 32/18. You will need to add some links or slide your wheel forward.
    He'll be just fine with 32x18. Why spend extra on a chainring, lessen clearance, with virtually no benefits?

  12. #12
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    Do you already have smaller cog or bigger chainring? If you don't want to deal with shortening the chain, try to fit 18t cog. If it doesn't fit I would get a bigger chainring.

  13. #13
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    You could just buy another chain to suit the 18T cog. It'd be cheaper than buying a whole new chainring i'd reckon.

  14. #14
    Ahhh the pain....
    Reputation: Raybum's Avatar
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    A 1 tooth change in the cog will move the axle about 1/8"...so going from 20 to 18 w/o changing anything else (chainring, chain), will move the axle back about 1/4". Obviously, if your chain is already super loose (chainslap), then it's gonna move more to properly tension it.

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