2019 Jeffsy 29 CF PRO RACE -8mm offset chainring?- Mtbr.com
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  1. #1
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    2019 Jeffsy 29 CF PRO RACE -8mm offset chainring?

    I just received & built my new Jeffsy pro race (e13 TRS carbon cranks w/ 32t ring)- I prefer a 30t chain ring instead of the 32t that it came with, but when I switched it to a 30t, I noticed that the chain ring it came with reads -8 offset (which I didn't know even existed and doesn't really make sense to me) - I tried to install the 30t which is for boost chainline - now the chain line seems way off skewed toward the drive side.

    I did a bunch of internetting and could not find anything explaining this or even anything about -8 offset chainrings. I was hoping somebody could explain what I am missing here?!

    Thanks!

    Update: Further internetting has led me to believe that e13 labels offset different than most other companies

    It seems that e13's -8mm offset = other's 6mm offset (non-boost) and e13's -5mm offset = other's 3mm offset (boost)

    e13 measures the offset from the inner edge of the cranks, while most measure it from what was once the standard, or "0" - they are really out to confuse us!

    So this explains why replacing the chainring w/ boost spacing moved the chainline 3mm out, but I still don't understand why this 2019 boost spacing bike is set up to run a non-boost ring?

  2. #2
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    I went 32t-30t on a 27 Pro Race and just ordered a 30t e13 SL Guidering to avoid any chainline problems. The SL Guidering is reversible, one side is boost and one is non-boost offset. I believe the Pro Race comes setup non-boost, the branding/logos are facing inward. Confusing I know, there was a long thread on PB about whether the 2017/18 Jeffsy should run boost or non-boost rings.

    All that said, I get massive chain drop from backpedaling in the biggest three cogs on my Pro Race with either the stock 32t or 30t so the chainline is not great.

  3. #3
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    Quote Originally Posted by gramboh View Post
    I went 32t-30t on a 27 Pro Race and just ordered a 30t e13 SL Guidering to avoid any chainline problems. The SL Guidering is reversible, one side is boost and one is non-boost offset. I believe the Pro Race comes setup non-boost, the branding/logos are facing inward. Confusing I know, there was a long thread on PB about whether the 2017/18 Jeffsy should run boost or non-boost rings.

    All that said, I get massive chain drop from backpedaling in the biggest three cogs on my Pro Race with either the stock 32t or 30t so the chainline is not great.
    Thanks so much for this response and explanation - I was getting frustrated with all the messing around and I could not get everything dialed in which is usually quick and easy for me - sounds like an issue w/ the bike which is disappointing but maybe not surprising w/ the mix/match drivetrain

  4. #4
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    "It seems that e13's -8mm offset = other's 6mm offset (non-boost) and e13's -5mm offset = other's 3mm offset (boost)"

    I don't know if the above is accurate, but SRAM boost chain rings are 3mm offset.

  5. #5
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    I replaced mine with an Absolute Black Oval 30t
    https://absoluteblack.cc/e13-oval-gu...ion-chainring/

    The offset was different than the factory chainring and I had to remove the spacers between the chain guide and the frame, but I haven't noticed any negative impact on shifting or any other drivetrain issues.

    Edit: Correction. After posting this I decided to double-check everything and discovered that I couldn't shift into the smallest cog on my e*13 cassette. After trying several adjustments, it just wasn't happening. I guess the good thing is, I never use that gear. But something people should know about.
    Last edited by hidperf; 01-16-2020 at 02:52 PM.

  6. #6
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    Deleted. Wrong thread.
    Last edited by hidperf; 01-16-2020 at 02:50 PM.

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