Chainring size vs BB spacers- Mtbr.com
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  1. #1
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    Chainring size vs BB spacers

    After building up my first SS, I'm trying to find the right gear ratio. 32/18 (1.78) is working great, but I'm looking to move up to 2.0 for some of the flatter trails. The plan was to move to a 36/21 (1.8) for normal riding and 36/18 (2.0) for flat trails. However, I have concerns about chainstay clearance with the 36t chainring. It looks like I'll need an extra BB spacer. As long as I fix the chainline, is there a rule-of-thumb about the maximum number of BB spacers? Minimum # of treads on the BB?

    Other option could be to go with a 16t in the back, but I worry about not having enough teeth engaged in the back. My tensioner only works in push-down due to geometry.

    Suggestions?

  2. #2
    Downcountry AF
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    I'll take a crack at it. One spacer should be within the acceptable range unless you already have two spacers on the drive side and are at the limit.

    What BB and crank are you using? If you think you need more threads engaged there are some options if you dig around. Like the Raceface X-type Team DH threaded BB (for Shimano style spindles or 24/24), it has a longer threaded part for deeper insertion into the BB shell and would allow you to run an extra spacer.
    Rigid SS 29er
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    Stop asking how much it weighs and just go ride it.

  3. #3
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    If you have a direct drive chainring, try flipping it, did that on my ROS9+ for tire clearance works great.
    Canfield Riot SS
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  4. #4
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    I've got a Raceface N/W crank and BB (initially was going to run 1x11, but thought better of it). Without tearing the drivetrain apart, I'm not sure if the chain will have clearance from the crank if I put the chainring on the inside of the spider. Maybe I'll give it a try and see.

    From what it looks like, I'd need 3-4 BB spacers leaving it as-is. Flipping the chainring seems a much better idea.

  5. #5
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    Quote Originally Posted by HaolErik View Post
    I've got a Raceface N/W crank and BB (initially was going to run 1x11, but thought better of it). Without tearing the drivetrain apart, I'm not sure if the chain will have clearance from the crank if I put the chainring on the inside of the spider. Maybe I'll give it a try and see.

    From what it looks like, I'd need 3-4 BB spacers leaving it as-is. Flipping the chainring seems a much better idea.
    I'd think 3-4 spacers would be way too much. The other crank arm would probably hit the frame too. They also make flat chainrings, which should offset the chainring 6mm or so.

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