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Boost frame spacing has a few benefits when it comes to frame design, but it alone is not enough reason to justify a new bike purchase. However, if you own a frame with 12 x 142mm spacing, you might have some questions when it comes to compatible drivetrain parts, specifically the crankset and chainring.

That seems to be the case with Kris, who wrote in an asked, “I have a bike with 142×12 rear spacing. I ordered a Boost Crank. Is this a major problem? A minor problem? Or, hopefully, no problem? Is there a consideration on ordering an 11 speed rear cassette? Thanks so much!”

That is a very good question which we decided to send out to our friends at Wolf Tooth Components. The WTC staff have grown to become one of our first sources for chainline related information since they have had to develop chainring that will work on so many different bikes and drivetrain configurations.

AASQ #47: Will crankset w/ Boost chainline spacing work for 12 x 142mm frame?

Image c. Wolf Tooth Components

From WTC:

Will it work? Yes. It would be better to use the right chainline though. There are a few  downsides of the chainring being 3mm more outboard than it should be:

  • The drivetrain (chain, cassette and ring) will wear out faster and have more drag in the bigger cassette cogs.
  • The chain will drop down when backpedaling when the chain hits the next shift gate (most 11 speed systems do this even at a non-boost chainline but they might make it a shift gate or two).

What can I do to improve the issue?

If you’re planning on running a 1x drivetrain with the new crankset, it may be possible to space the chainring inboard 3mm to reverse the effect of the Boost spaced crank. This may be able to be done using different chainring bolts and/or spacers between the crank arm and the chainring (or moving the chainring from the outer position to the inner if a 2x/3x crank). Or, if you have a crankset with the option of running a direct mount chainring, you may be able to purchase a chainring with a different offset that will bring it back to non-Boost specifications as well.

To get back to the original question, you could probably call it a minor problem but one that won’t leave you unable to ride your bike. It may lead to accelerated drivetrain wear and cause backpedaling problems, but there are also ways around the issue if you’re willing to play with some different chainring and/or bolts and spacers.

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7 comments

  1. Justin White on

    You just had to say “If you space the ring 3mm inboard, then yes. Otherwise it will behave badly in the large cogs.”

    You didn’t need all that marketing wank from WTC: those chainline numbers don’t match every other reference, which says 142/135 hub ideal chainline is 49mm and 148 hub ideal chainline is 52mm. They’re basically saying Boost cranks don’t need to exist, because existing non-Boost cranks already have 49mm spacing…

    If fact, if you follow WTC’s recomendation, a Boost Crank with a 3mm offset direct mount chainring that is flipped around would give that 46mm optimal 142 hub chainline.

    Reply
      • Ricky Bobby on

        Correct. Wolf Tooth does make a bunch of offset chainrings, so there is likely a solution, but if possible, and depending on your mounting, you can get spacers from McMaster Carr to do the trick, also Problem Solvers.

        Reply
  2. Bmx on

    My hope boost ring is 3mm in board , ie towards the frame. A 3mm spacer between the crank arm and the bb would bring it back out 3mm , better off returning it altogether as this isn’t really an ideal setup.

    Reply
  3. miked on

    Not possible to answer this question until we know what brand/model we are talking about. If the crank has a direct mount chainring, its not a boost crank, its just a crank sold with a boost (offset) chainring. Assuming it is direct mount, original question asker just needs to sell his chainring and buy the correct offset ring.

    Reply

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