Shimano crank 4 bolt pattern query

skeetam
skeetam Posts: 178
in Workshop
Is the Shimano crank 4 bolt pattern on Ultegra 6800 and R8000 the same?

The reason I ask is, I've got some oval chainrings for a 6800 crank that I'd like to fit to a new R8000 crank spider with a PM on it. Thanks.

Comments

  • akh
    akh Posts: 206
    edited December 2020
    The bolts themselves are, but unfortunately the arms and chainrings aren't compatible as standard.

    Shimano have put a sticky out bit on the new cranks to stop an older chainring being mounted. This video of AbsoluteBlack oval rings shows it quite well because of the colour contrast. You can clearly see where the newer style rings have a swept cut out to accept the protrusion.

    **EDIT** the video didn't link at the right timestamp, skip to about 03:50 for the most relevant bit

    https://youtu.be/RmJm8nemLAs?t=232

    The newer rings are backwards compatible though, R8000 compatible rings work on the older style cranks, you just have a bit of a cosmetic gap (as in the above linked video).


  • skeetam
    skeetam Posts: 178
    Great, thanks.

    The older cranks have a slight curve which the newer ones do not so to get them to fit, I'll have to Dremel the curve into a straight line. Will report back when I've done it.

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