Lot's of runout in XT 760 cranks?

Are you saying the you contact one side of the derailleur while in the small cog, and the other while in the large cog....

Or are you claiming that your large ring is so out of flat (planar) that you contact both sides of the derailleur simply by turning the cranks in a full revolution (without changing cogs)?


Are you sure that your front derailleur is installed correctly (height, angle)? Are you sure that your bb spindle is not causing the runnout..ie spacer set-up is correct and the spindle is not able to move side to side?

Lastly, I dont think it would be a big surprise to buy used cranks and have the big ring bent...That is the first part that would contact something (log, rock, etc) and see damage.

The big ring travels side to side as it revolves.

davep said:

Or are you claiming that your large ring is so out of flat (planar) that you contact both sides of the derailleur simply by turning the cranks in a full revolution (without changing cogs)?

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Exactly that. I had a road bike once that did this too, but not so much. I only noticed it when looking down on it--it didn't rub. From what I understand, some runout is normal except, ideally, in SS or track cranks.

davep said:

Lastly, I dont think it would be a big surprise to buy used cranks and have the big ring bent...That is the first part that would contact something (log, rock, etc) and see damage.

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Everything is tight and adjusted, it's not the spindle moving in the BB shell. The big ring is brand new so it isn't bent.

My FD might be a smidge too high on the ST. I'll check that!