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  1. #1
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    Questions About Chainrings

    I have a 2008 Giant Reign X0 that I bought used last April, and it's been a blast to ride it on local trails. It was ridden pretty hard by both me and the previous owner, so now the chain, cassette, and chainrings are worn out to the point that the bike is not rideable anymore.

    I picked out a new chain and cassette, but I am a little confused about the chainrings. This is the only part that I can't figure out what I currently have on my bike. I only know that they are 24/36 tooth. My questions are:
    1. How can I find out what bolt center diameter (BCD) I need?
    2. Am I supposed to buy each ring separately or are the two supposed to come together?


    Thanks

  2. #2
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    Easiest way is to look up the model of the crank you have.
    Most 4 arm MTB cranks are 104 for the large rings and 64 for the granny.
    From here, Sheldon Brown's Bicycle Crank/Chainring Bolt Circle Diameter Crib Sheet
    A 104 BCD crank will measure 73.5 between the bolts and 64 BCD will measure 45.3
    Depends on who you buy the rings from - some can be purchased as a set, others individually. Should get them from same manufacturer/model so the ramps and pins line up.

  3. #3
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    Okay, I looked closer and it says on the bash guard in very small text that the bigger ring is 104 BCD. Is it safe to assume the smaller one is 64 BCD? I looked at the smaller one too and the only things labeled on it were "24T" and "X TYPE". The crank I have is the Race Face Atlas, but I can only find specs for the newer versions. Mine is from 2008.

  4. #4
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    Quote Originally Posted by s11s11 View Post
    Okay, I looked closer and it says on the bash guard in very small text that the bigger ring is 104 BCD. Is it safe to assume the smaller one is 64 BCD? I looked at the smaller one too and the only things labeled on it were "24T" and "X TYPE". The crank I have is the Race Face Atlas, but I can only find specs for the newer versions. Mine is from 2008.
    you are correct.

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