Hey everyone, welcome back!
The modern bikes of today are requiring not only different rear spacing for our hubs
but also different chainlines.
As you probably know SRAM is dealing with this in part by giving us
different offset chainrings and also a WIDE version of their cranks.
But what about Shimano?
How are the current 12-speed drivetrains dealing with this? Let's check it out!
And the reality is Shimano with their 12 speed drivetrains they finally introduced Direct Mount chainrings.
However all the chainrings are the same and the difference is in the cranksets,
and you see the 3 models of the SLX here, the M7100, 7120 and 7130.
Interestingly you're not going to see 49 mm chainline here anymore, 49 millimeter was for non-Boost frames.
But what they say is that M7100 is for 52 mm so that's a Boost 148 mm frame
Q-factor is 172 mm and this should be used with the old 142 and 135mm rear spacing as well.
This is still for Boost, M7120, however this provides you with the 55 mm chainline
for bikes like my YETI that need more tire clearance, so they have to go wider here at the spindle.
Finally Super Boost Plus or 157 mm,
that's where you're going to need the M7130 that gives us a 56.5 mm chainline and 181 mm Q-factor.
So again Boost and non-Boost, Boost with more tire clearance and Super Boost or 157 mm hub spacing.
They recommend using the same Bottom Bracket for all these cranks, for threaded BBs both 68 and 73 mm BB shells.
As for Press-Fit it's the same, BB-MT800-PA Press-Fit, both 89.5 and 92 millimeter BB shells.
Chainring is not mentioned anywhere in here because for SLX, XT and XTR it doesn't come with one automatically.
But you can obviously order some of the chainrings that Shimano makes for their cranks.
They're direct mounted, XT and SLX chainrings are identical, or
order some 3rd party chainrings like this oval,
more and more manufacturers like Wolf Tooth have chainrings for these new Shimano cranks
and that's great news because they can offer ovals,
lower weight and maybe more offset options in the future.
And talking about Shimano chairings they are all looking kind of the same as this with a few variations.
Obviously the tooth profile is the DCE+ so Dynamic Chain Engagement,
that's their version of the narrow-wide tooth profile.
And with all these chainrings having the same offset, the difference must be
in the spindle length that they provide their cranks with.
Which also means that the non-drive side or the left side crank arms should be identical between these 3 models.
This is a M7100 for 52 mm chainline which is really tight on this frame by the way.
But if we look here on the non-drive side crank arm,
you're gonna see M7100 but right underneath M7120, M 7130 confirming my assumption.
In the box I have this M7120 for 55 millimeter chainline
and yeah, they provide a user manual but if you look at this non-drive side,
M7100 is what it says on the crank arm, but 7120, 7130 are mentioned in there as well,
just like we saw it on the other crank arm.
Also in the box you're gonna get this Shimano TL-FC41 tool,
this is needed to install and remove the new chainrings so yeah, it's another tool,
and you're also going to get these:
the preload adjuster nut for your non-drive side crank,
you're going to get this Lock Ring for your new direct mount chainring,
and finally you're gonna get two 3 mm spacers.
I'm gonna be installing this absoluteBLACK oval on my cranks
and from the lock ring you're gonna see that this is for SLX and XT only
and you need to tighten it to 35-50Nm.
Obviously you're going to need the tool that I just mentioned to accomplish that.
This tool, actually the whole Direct Mount idea is new for Shimano.
Remember the Q-factor difference between M7100 -M7120 is 6 mm, 172 versus 178mm,
and the chainline difference is 3 mm, 52mm versus 55mm.
The Q-factor means the distance between the outside of each crank arm so where your pedals get connected.
And this spindle should be longer or shorter by 6 mm compared to my M7120.
And measuring it, the M7100 spindle comes up to 115 mm long
and M7120 comes up to 121 mm long,
so 6 mm difference hence the two spacers that they provided with this crankset,
each 3 mm that have to be installed on both sides of my bottom bracket.
Aside from installing one of these spacers on each side of the bottom bracket
and by the way there is a rubbery face to it, make sure you put it against the bottom bracket,
so aside from that the installation of these crankarms is quite simple
and I have it documented, I'll make sure to link it.
But you can see how the 55 mm chainline versus 52 mm gives me a lot more room here on my bike.
You can see how I can install the oval now whereas before I couldn't even dream about it.
So that's the 3 mm spacer that's now installed right there on the drive side
but that's only possible because the spindle of these cranks is longer by 6 mm.
If you're wondering how extreme is the 55mm chainline on a 12 speed drivetrain from Shimano,
I'm not dropping the chain from the largest cog, the 51T,
it is extreme indeed as you can see it here but I guess it would be usable.
This is how that chainline looks like from this other side,
obviously not less extreme, this bike has a 433 mm chainstay.
If your bike has even shorter chainstays, 55 mm chainline might be a bit too much.
Chain is on a straight line from the chainring to the cassette right here on the 5th cog from the smallest
so I guess if you were to use two thirds, 75% of the cassette right here nothing's too extreme.
That chainline gets more extreme obviously when you make it to the 51 tooth.
This wouldn't be any different than what Shimano recommends for their non-Boost frames
which is the use of these M7100 which is a 52 mm chainline.
So I just hope that Shimano tested the heck out of it and it works okay long term.
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But back to our chainline discussion, you can see how Shimano is using different spindle lengths for all these standards,
for Super Boost they have a longer spindle and just 4.5 mm spacers instead of 3mm.
That's how they address the need for more gears, more tire clearance and better bracing angles on our wheels,
that being given by Boost or Super Boost these days.
We did use SLX cranks for our discussion today but if you were to look at the 12 speed offering from Shimano today
the principles we discussed about chainline and Q-factor apply for their entire lineup from Deore to XTR.
Are you folks using 52 mm chainline for your non-Boost frames?
What about Boost frames, do you use 55 mm chainline or the 52mm given to me by the M7100?
I would love to hear your opinion, as usual don't forget to comment in the section below,
and until next time, hope to see you folks on the trails.
Cheers guys, cheers!