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Hey guys,

In converting my M532 Deore to 2x9 use the other day, I had to add a 1.5mm spacer in order to get adequate clearance between the chainring and stay.

I was concerned about this, so I measured the difference from the outside of the right crankarm to a bottle cage bolt when the crankarm was in the 2 o'clock position. I did this again with the left side.

To my shock and horror, the right side was 9mm further off-center than the left side. It might not seem like much, but coming from the road, with a 146mm Q-factor, it's noticeable. The chart I've attached shows that it is common for there to be a difference between the sides of a Shimano external bearing crankset; usually with the 26-36-48t setup that is available in XT and LX configurations. This results in a 87.5/94.0mm and 87.7/94.20 ratio, respectively.

Now, that makes sense; they need clearance for the larger chainrings that those units provide. However, XTR M960 cranks are 84/84, XT M760 are 87.5/87.5, and LX M580 are 87.7/87.7.

Does anyone have:

A) an explanation as to why Q goes up as the crankset level goes down
B) any idea if the chainlines are exactly the same, but Q increases further down the line?

I'm asking because I'm running a 26/36 setup on the granny and middle ring. I want to get an XTR crankset, put a spacer in, and run 26/38 without a ridiculous L/R offset ratio.
 

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