Direct Mount Chain line/Chainring Help!- Mtbr.com
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  1. #1
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    Direct Mount Chain line/Chainring Help!

    Hello All,

    I could use a bit of help. I have a 2020 Marin Rift Zone Carbon 2.
    The bike is currently running a XT rear derailleur and cassette, and up front it is running a FSA Gradient modular crankset and chainring.

    After buying the bike I noticed that the chain line could be improved.
    Its current Chainline is 53mm (which is at the extreme end of boost) and I would like to bring it inboard by 1 mm or 2 mm.

    Can anyone suggest a Chainring the would work?

    My current chainring is a 32T 6mm offset (I think) there is no stamp on the chainring showing the offset.

    *Note 1* the FSA gradient crankset can move inboard by 3 mm by itself using a spacer. But 3 mm seemed to put the chain ring to close to the chain stay for comfort. Does anyone know of a 2mm or 1mm spacer for these cranks?

    *Note 2* I have been looking at the Wolf tooth Camo system or Garbaruk Chainring. Maybe someone from the community would be able to measure the dish on either of these chainrings so that I could see the offset.

  2. #2
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    I agree moving it inboard isn't a bad idea, but IMO, 1-2mm will have no significant effect on anything. The only possible effect will be very slightly less tendency to derail when backpedaling in the lowest gears. What do you hope to improve by doing that?

    When I got new rings for my boost bikes, I got non-boost offsets (3mm closer chainline), but I wouldn't replace a good existing ring just to change the offset.
    What, me worry?

  3. #3
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    Quote Originally Posted by Lone Rager View Post
    I agree moving it inboard isn't a bad idea, but IMO, 1-2mm will have no significant effect on anything. The only possible effect will be very slightly less tendency to derail when backpedaling in the lowest gears. What do you hope to improve by doing that?

    When I got new rings for my boost bikes, I got non-boost offsets (3mm closer chainline), but I wouldn't replace a good existing ring just to change the offset.
    Well the FSA Gradient crankset has the ability to switch a spacer moving the chainring from boost to non-boost. I've tried this and it did move the chainring inboard but it left only a 1.5mm to 2 mm gap between the chain stay and chainring. I questioned if that was too close?

    I guess let me ask the members here .... is a 1.5mm gap between the chainring and chainstay too close?

    However while testing that configuration, the Chainline did seem to improve. (But I didn't have a chance to ride the bike and test for frame flex)

    Another option I guess.... would be to downsize the chainring from 32t to 30t (giving more chainstay clearance) and then move that spacer. Effectively giving myself a bit more space.

    Thoughts?

  4. #4
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    You cheated. You added those two notes after I posted. It'd have been better etiquette to add a post with that info after mine.

    IMO, 1.5mm is cutting it kinda close. Dropping 2 teeth on the ring will reduce its radius 4mm. It will help but how much that increases clearance with the chainstay depends on the angle between the ring and chainstay at that point. For example, if it's 30 degrees, it'll increase clearance by 2mm for a total of 3.5mm, which is better.
    What, me worry?

  5. #5
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    Quote Originally Posted by Lone Rager View Post
    You cheated. You added those two notes after I posted. It'd have been better etiquette to add a post with that info after mine.

    IMO, 1.5mm is cutting it kinda close. Dropping 2 teeth on the ring will reduce its radius 4mm. It will help but how much that increases clearance with the chainstay depends on the angle between the ring and chainstay at that point. For example, if it's 30 degrees, it'll increase clearance by 2mm for a total of 3.5mm, which is better.
    Lol no cheating on purpose here just edited my English cause I suck at it! And I am self critical on it.

    But anyway I see your point.
    The clearance between the chainring at stock is about 4.5mm to 5mm so that's why I'm hoping to move it inwards only 1mm or 2mm.

    The agle between the chainring and chainstay is rather flat how ever it does slightly progress as it gets closer to the bottom bracket. I will have to subtract 4mm from the current radius and see what that angle is. I'll report back.

    Thanks

  6. #6
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    Yeah it won't work, I just took measurements and I would need a 28t or 26t ring to make it worth it... And I live in Wisconsin not many extreme mountains in these parts.

  7. #7
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    I'd still be interested to hear if anyone has experience with the chain rings that seem to have a greater offset inwards

  8. #8
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    change your cr so that you use the gears With the best chainline the most

    That should be all you need to do. Also to expand you time in those gears, switch to an oval.

    I suppose that the cr position is optimized for the widest tire that will fit, but it also keeps the chain a little cleaner by moving it a bit more from the tire edge.

    Hope that helps.

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