Hi everyone!
If you've been exposed to the Shimano 12 speed drivetrain as of late,
you probably know that they have to offer
two versions of their derailleurs:
One for the 1x12 drivetrains,
second one for the 2x12 drivetrains.
I have them with me today.
I have the RD-M8100-SGS right here on the right
and this is something that I've reviewed recently.
And on my left I have the SLX, the RD-M7120-SGS.
What's the difference between them?
What are the design differences between the two?
Let's take a closer look.
Shimano blurred the waters on this quite a bit because when they launched it,
they had this XTR M9100-GS or medium cage
that was good for 11 and 12 speed,
with cassettes up to 45 teeth.
Shortly after introducing it,
Shimano dropped the 11 speed drivetrains altogether
and today we have two cassettes:
a 10-51t or wide range cassette,
a 10-45t or Rhythm Step cassette,
and we have two derailleurs:
one for 1x12, and one for 2x12.
Cable routing is similar but not identical.
All these parts here have been redesigned,
B-gap adjustment screw on both,
then you see the limit screws,
these are in a different spot,
and that is mostly because this whole middle section of the derailleur,
which is the parallelogram,
the area between these four bolts that moves up and down,
it's actually larger on the 2x derailleur.
Clutch is the same, clutch lever it's going to be the same,
the next thing that is different is the bumper here on the 1x derailleur.
This is only useful to silence the drivetrain when on the smaller cogs.
Here at the back is where you'll notice the biggest differences between the two.
First of all, these are both SGS or long cage derailleurs,
However if you were to measure them,
1x derailleur, the distance between the two jockey wheels is 9.5 cm,
and that's about the same length as the SGS 11 speed derailleurs from Shimano
The 2x derailleur has 10.5 cm between the two jockeys
so definitely this is a longer cage even though it's considered to be a SGS as well.
The third derailleur that Shimano has only in the XTR line
is the RD-M9100-GS that has this distance shorter by 28 mm.
So, as you can imagine, you would have the whole derailleur going all the way down to here.
Making for a really nice and stubby 12 speed derailleur.
At the top of the cage is pretty obvious that the offset of the two derailleurs is quite different.
The 2x has about 3 cm between the axle of your guide pulley and that pivot point.
The 1x derailleur has 4.5 cm so about 50% more offset.
This allows the 1x derailleur to operate properly with a wider range cassette
That's why this is meant for the 10-51t cassette
and the other one is meant for the 10-45t.
Offset on both of these is actually bigger than what we had on the old 11 speed derailleurs.
The offset over here is only about 2 cm
and look at the difference between the cage length.
This is a M8000-GS 11 speed
and that's your M7120-SGS 2x12. Wow!
Otherwise both cages are bent and twisted
which makes for better chainline throughout the wide gear range.
Out of the three 12 speed product lines XTR is the only one giving us
one derailleur for 10-45t cassette,
another derailleur for 1x12 with 10-51t cassette
and the third one for a 2x12 speed drivetrain.
SLX and XT keep it simple by offering only two derailleurs:
The M7120 and M8120 derailleurs take care of that 10-45t cassette,
whether you use it with 1x and 2x drivetrains
With 1x I would argue that this is a compromise to save on the number of SKUs.
because this cage is extra long and there's no need for it in that combination
As opposed to that, I would guess this M8100 is going to be the bulk of the Shimano sales
definitely because it works well with the 10-51t cassette,
which I also believe that's going to be the bulk of their sales as opposed to the 10-45t.
What about you folks?
Is anybody using a 2x12 drivetrain out there?
I would love to hear!
As for me, I've been using this type of derailleur
with Shimano 10-51t or 10-50t cassette from SRAM,
and have a few videos about that.
If money was not a problem
I would probably get the short cage XTR derailleurs and the 10-45t cassette
for most of my bikes,
only because that range is good enough for Ontario.
Let me know if you have any questions in the comments below.
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And until next time,
I hope to see you folks on the trails
hopefully riding some Shimano gear.
Cheers guys!