# XT FC-M785 Crank Specs.



## Clockwork Bikes (Jun 17, 2006)

Does anybody have tech. docs for the Shimano XT FC-M785 2-ring crank? Specifically I'm looking for the X,Y locations for the chainrings and crank arm.

Their website comes close but doesn't quite get this detailed.
Product

Thanks, Joel


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## pvd (Jan 4, 2006)

y1-83.6,y2-59.5,y4-35.4,cl-48.5,x1-50.3,x2-42.3,x4-41.4,x5-66.0,x6-66.0


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## Clockwork Bikes (Jun 17, 2006)

Perfect. Thanks!


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## Peter E (Feb 16, 2004)

what are those numbers?


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## Clockwork Bikes (Jun 17, 2006)




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## Blaster1200 (Feb 20, 2004)

What I don't understand is why the specifications for the XTR M980 cranks is so different than what the cranks actually measure.


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## Yogii (Jun 5, 2008)

You guys speak a completely different language! Happy New Year...


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## whydomylegshurt? (Jul 28, 2004)

Blaster1200 said:


> What I don't understand is why the specifications for the XTR M980 cranks is so different than what the cranks actually measure.


What I was told by a contact at Shimano was that the spec for the M980 cranks "included the required clearance". I can't say 100% if it's true as I bailed out of the industry right before the cranks became available. All I know is that's what I was told when figuring out OEM build kits.


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## Blaster1200 (Feb 20, 2004)

whydomylegshurt? said:


> What I was told by a contact at Shimano was that the spec for the M980 cranks "included the required clearance". I can't say 100% if it's true as I bailed out of the industry right before the cranks became available. All I know is that's what I was told when figuring out OEM build kits.


I was thinking that there was a change in idealogy. The 980 3x10 (I think I misquoted the crank model number before, but it's the 28/40 double that I measured), has the same specs as the 970, which measure out correctly. When I was measuring the double, it seemed like there was plenty of clearance to allow a chain to go through. What you're saying is that Shimano's now including clearance into the specification instead of the hard measurement makes sense with my findings. Though I wish they would stick with the hard numbers.


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## zank (May 19, 2005)

pvd said:


> y1-83.6,y2-59.5,y4-35.4,cl-48.5,x1-50.3,x2-42.3,x4-41.4,x5-66.0,x6-66.0


The 785 26/38 crank I have here in the shop measures 73 mm for the x5 and x6 and an overall Q-factor of 176 mm.


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## zank (May 19, 2005)

Blaster1200 said:


> I was thinking that there was a change in idealogy. The 980 3x10 (I think I misquoted the crank model number before, but it's the 28/40 double that I measured), has the same specs as the 970, which measure out correctly. When I was measuring the double, it seemed like there was plenty of clearance to allow a chain to go through. What you're saying is that Shimano's now including clearance into the specification instead of the hard measurement makes sense with my findings. Though I wish they would stick with the hard numbers.


The 980 (24/32/42 and 26/38) should measure the same Q as a 970. The 985 Q should be 6 mm narrower. You found the 985 28/40 the same as a 970? Sorry to be redundant. Just trying to clarify. Interesting if that is the case. The narrower Q was one thing they really pitched as a selling point for the 985.


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## Blaster1200 (Feb 20, 2004)

zank said:


> The 980 (24/32/42 and 26/38) should measure the same Q as a 970. The 985 Q should be 6 mm narrower. You found the 985 28/40 the same as a 970? Sorry to be redundant. Just trying to clarify. Interesting if that is the case. The narrower Q was one thing they really pitched as a selling point for the 985.


Sorry, I wasn't very clear. I'm not referring to the Q, but chainring clearance from centerline (X1, X2, or X3 - well...only the X for the double) of the 28/40. And making matters even more confusing in my post, is that I can't seem to remember the new XTR numbers and quote them correctly (980/985/986/988, etc).

The 28/40 does have a narrower Q than the triple 970/980. Of course, the 26/38 double is the same Q as the triple.


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## thomasbs (Jun 16, 2012)

*This is confirmed:*

FC-M770 Q-factor: 172 mm
FC-M785 Q-factor: 172 mm

I have measured it by umounting the chainset and flipping the right arm 180 degrees.

In other words: the "optimized Q-factor" for the M785 double (advertised by Shimano) is *exactly the same as for the old triple* (and I imagine for the FC-M780 triple as well).

*What we can learn from this:* 
If your frame can accommodate it, you get a better chain line and the exact same Q-factor by converting an triple XT chainset (eg. M770, M770-10 or M780) to a double by removing the outer ring and put your preferred size ring in the middle position and a larger-than-22t granny in the inner position (eg. 42-28).

The BCD are all the same (104/64), som the only problem I can see, is if the spacing between the rings differs by a fraction of a mm - this may or may not give shifting problems, but I hardly think so. I will try to get accurate measures for this later.

*Who should buy the double version?* 
If your rear chainstay is too wide to accommodate a large enough inner ring (eg. 28t), then the double will probably give you the clearance you need.

Since my frame has lots of clearance, I will probably put the 40t in the middle position of my old M770 and use the 28t in the inner position.

Cheers,
Thomas


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## coconinocycles (Sep 23, 2006)

If you are under 88mm overall width of the chainstays @ 50mm from the BB shell you are A-OK.
- Steve Garro, Coconino Cycles.


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## j-ro (Feb 21, 2009)

coconinocycles said:


> If you are under 88mm overall width of the chainstays @ 50mm from the BB shell you are A-OK.
> - Steve Garro, Coconino Cycles.


I'm going to write an app to copy this and laser paste it directly to my shop wall


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## coconinocycles (Sep 23, 2006)

j-ro said:


> I'm going to write an app to copy this and laser paste it directly to my shop wall


I'll post a picture of my wall heater - it's got tons of these written on it.
- Steve Garro, Coconino Cycles.


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## InertiaMan (Apr 16, 2004)

Anyone have a more recent version of the photos above, specifically the X dimensions for newer cranks, ideally including the most recent Boost versions? But even M780 and M782 and M785 crank X dimensions would help.

I'm diddling around w/ various 2X/3X crank variations for some Boost rear spacing frames and trying to anticipate what will work best.


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## Walt (Jan 23, 2004)

Nope. Shimano hasn't released tech specs in years AFAIK. 

-Walt


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## DSaul (Dec 13, 2012)

I don't remember where I found this, but it is the 2015-2016 tech doc for all the Shimano components. It is a huge PDF file, so here is a Google drive link to the file.

https://drive.google.com/open?id=0B-GqT5xP2oqNYy1aVmhHOGhjQnM


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## InertiaMan (Apr 16, 2004)

Very helpful @ DSaul, many thanks for the document.


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