Shimano 12-speed MTB Cranks Chainline

I am thinking of building a new carbon hardtail and I would like to equip it with a 12-speed Shimano crankset (SLX, XT or XTR). Now I see that Shimano offers all Cranks with three different chainline options: 52mm, 55mm and 56,5mm.

The Frame ist Boost 148mm standard.
Bottom bracket is PressFit BB92.

Is there any way to determine which version will be best suited? I read that 56,5 is only for “Super Boost”, but 52mm and 55mm will be both fitting for Standard boost factor. So I am unsure which one to pick.

I just replaced my M7000 cranks with M7100

The older M7000-B 11 speed boost is I believe 53mm

Went with the 55mm M7120 initially (which comes with a stupid washer that goes on the spindle and looks like it will pickup dirt seems like a cheap design to me). Chain seemed to want to come off when I back pedalled and the Q factor is also a lot wider.

Managed to return it and get the regular M7100 non-boost version for 52mm which works much better IMO and has a nicer for me narrow Q factor. Some googling somewhere told me that the M7100 can be used for boost and non-boost.

thanks for the reply. I also looked at the Q-factor and would definitely also prefer the narrower Q-factor. Still, I find it strange that there is no clear statement on when to use which chainline version. Seems like both (52mm and 55mm) will be working somehow with boost factor!?

I think a lot depends on your frame. Are you sure you’re going to have enough clearance between the chainstays & the crank arms with the smaller Q/chainline? I’m pretty sure you will but what about with a crank arm based power meter should you ever choose to go that route?

My Orbea Oiz came specced with XT 8120’s & I’m glad it did. Despite being a smaller guy at 5’5”, I like a wider Q (I’m duck footed & always have trouble with my inner heels rubbing seat stays; I’m actually running 16mm pedal spacers, too) Plenty of room for my Stages left arm pm.

Just wanted to throw in a few more things to consider other than chainline.

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What did you go with? I am working on a new crankset for a Chisel, and plan to go for narrow q-factor. Debating between the XT 8100 (if I can find it) with the 172mm q-factor; or springing for the XTR 9100 for that road-like 162mm q-factor.

Any recommendations from anyone?

Went with the narrowest q-factor (52mm Version) and it shifts fine in every situation.