Anyone using a FC-M8100 on a non-boost frame?- Mtbr.com
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  1. #1
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    Anyone using a FC-M8100 on a non-boost frame?

    Back when the Shimano 1x11 drivetrains first came out, there were lots of people that experienced poor shifting on non-boost (142 OLD) frames unless they added chainring spacers to bring their chainline down to 49-50mm.

    The newer Shimano FC-M8100 12-speed cranks have a 52mm chainline spec. However, Shimano claims it's compatible with both boost and non-boost frames. The 52mm chainline can't be optimal for a non-boost frames. But maybe it still works ok because of all the other changes Shimano made to their 12-speed drivetrains (new cassette tooth pattern, angled derailleur cages, different chain profile, etc). Maybe these changes make the drivetrains a little more forgiving of a poor chainline.

    I have a non-boost frame that I'm thinking about converting to 12-speed drivetrain. Has anyone out there actually tried a Shimano 12-speed drivetrain with the M8100 crank on a non-boost frame? How's the chainline look, particularly on the largest cassette cog? Any shifting problems?

    I really like the design of the M8100 crank but there doesn't seem to be anyway to tweak it's chainline with spacers because of the direct-mount chainrings.

  2. #2
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    I don't have the answer but this confuses me as well. What is the best chainline for boost? 52 or 55m???

    M8100 crank is 52mm chainline, 172mm Q-factor - claimed to be for boost and non boost

    M8120 crank is 55mm chainline, 178mm q-factor - claimed to be for boost

    M8130 crank is 56.5mm chainline, 181mm q-factor - claimed to be for super boost

    8100 https://bike.shimano.com/en-NZ/produ...C-M8100-1.html
    8120 https://bike.shimano.com/en-NZ/produ...C-M8120-1.html
    8130 https://bike.shimano.com/en-NZ/produ...C-M8130-1.html

  3. #3
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    Quote Originally Posted by dave_rh View Post
    I don't have the answer but this confuses me as well. What is the best chainline for boost? 52 or 55m???
    This Wolf Tooth article claims that the ideal chainline for a boost hub is 49-50mm.

    But neither Shimano or SRAM follow this. And I assume their engineers know what they are doing. Instead they seem to have settled on a 52mm chainline for boost hubs and tweaked their drivetrains to work well with that.

    The corresponding chainline for a non-boost hub would be 3mm less or 49mm. That's because a non-boost hub is 3mm narrower on each side.

    Given the above, it's surprising that Shimano says that the 52mm chainline of the FC-M8000 can work with non-boost hubs. That's why I'm curious if anyone has tried it.

  4. #4
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    according to shimano the 11 speed FC-M8000-1 has a chainline of 50.4mm

    https://bike.shimano.com/en-EU/produ...C-M8000-1.html

    the FC-M8000-2 crank for 2x has a chainline of 48.8 with PCD of 96/64

    https://bike.shimano.com/en-EU/produ...C-M8000-2.html

    Funny thing is, I heard that these were identical cranks and could take either a 1x or 2x arrangement.

    maybe it might work using a FC-M8000-2, with a 64PCD chainring?

  5. #5
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    Quote Originally Posted by dave_rh View Post
    according to shimano the 11 speed FC-M8000-1 has a chainline of 50.4mm

    Funny thing is, I heard that these were identical cranks and could take either a 1x or 2x arrangement.
    I am also considering the FC-M8000 and have looked very closely at it. Yes, the 1x model is exactly the same as the 2x model. The only difference is that the 2x model comes with chainrings.

    Also, the advertised chainline of 50.4mm is a little misleading. You only get that with the 11-speed chainrings that Shimano sells for it. These have raised tabs near the mounting screws that act like 2mm chainring spacers. Otherwise, the chainline is about 52mm, the same as the FC-M8100.

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