Can I put a stages XTR 9100 left side power meter on a XT 8100 crankset? Seems like it should work, but haven’t found a clear yes answer.
MaplePanda is correct, M8100 is incompatible with M9100.
From the Stages website (emphasis added):
SHIMANO HOLLOWTECH II MOUNTAIN BIKE
For Shimano Hollowtech II mountain bike cranks, compatibility is a bit more difficult due to changes in the left crank between versions. If you are unsure, please submit a new ticket with Stages customer support detailing your current bike and crank model.
Current models (as of Mar 2023):
- XTR M9100 12-speed: Works only with M9100/9120 cranksets, which do not use a pinch bolt attachment system on the left crank.
- XT M8100 12-speed: Works only with M8100, M7100, and similar 12-speed Shimano mountain cranksets that feature two pinch bolts and are 20 mm thick at the BB end. Also works with older XTR pinch bolt style cranks.
Since Ted covered the main points, I shall provide some supporting information and visual aids, as promised.
The XTR FC-M9100 and -9120 cranks feature a single-bolt attachment for the left crank arm.
This mates with short, relatively large splines on the crank spindle.
For comparison, XT FC-M8100 and its relatives (-8120 and -8130) use the older style of left arm attachment, featuring two pinch bolts and a split.
This mates with a relatively long section of small splines.
This is the same joint design as XTR FC-M9000 and -9020.
Lastly, for comparison, let's examine XT FC-M8000 (also -8020). It has a wider left arm interface than both the 12 speed stuff AND the 11 speed XTR (for reference, see the gap between the pinch bolts). The difference is only a few millimeters, but that's enough to make the cranks non-interchangeable. The first image shows M8000, the second M8100.