I have the opportunity to purchase a left sided power meter for a decent price, that is a newer FC-R8000 arm, whereas my bike currently has Ultegra FC-6600 equipped. My assumption is that because it is only left side it should work, but I would like to gather secondary opinions before I bite the bullet. Thanks!

  • Yes, it’s a fit.
    – Noise
    Commented Jul 25, 2022 at 20:16
  • 1
    @Noise Make that an answer?
    – Weiwen Ng
    Commented Jul 25, 2022 at 20:38
  • 1
    Remember - its very hard to see both sides of the bike at the same time, so aesthetics don't really matter. As long as they're the same length.
    – Criggie
    Commented Jul 25, 2022 at 20:45

1 Answer 1


Compatibility between Hollowtech II crank arms is a sure thing if you are fitting road to road (not forgetting the spacer for triple) or mountain to mountain. Therefore you'll be fine with a new Ultegra on an old Ultegra. Minor details can change, Q-factor by a very small amount for instance, but it is unlikely to be detectable to you the rider and won't have an effect on frame clearances.

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