Bikepacking gearing with GRX Di2

[ooo]

Sooo I'm guessing there's something preventing me from using shimano's XT cranks? Something like this https://bike.shimano.com/en-EU/product/ ... 00-B2.html 36-26T would give me a really nice spiny setup for bikepacking and looks in line with tour divide rigs.

From the Shimano FC-M8000-B2 page (https://bike.shimano.com/en-EU/product/ ... 00-B2.html): "Chainline 3 mm outboard, . - It requires special dimension of frame which cassette position and front derailleur mount position are 3 mm outboard., . - Only E type and D type front derailleur are compatible with the special frame"

I'm actually going to be building this thing...apparently the 3mm outboard chainring is just to accommadate Boost spacing which is required by the Cutthroat's frame dimensions, therefore XT cranks should work. Now I'm just wondering about XTR vs GRX di2 front and rear derailleurs. Planning on running a 26/36T front with an 11-40 rear.

Cutthroat seat tube is square with braze-on road FD mount - it looks like you can't mount mtb FD on it. Salsa website quotes:

Frame Spec: "1x MTN Boost: 40t Max; 2x RD Boost outer ring: 46–50t, inner ring: 30–36t"
[- mtb boost is 1x only (no 2x mtb boost); "RD Boost"="road boost"]

Frame Q&A: The modern Cutthroat is designed around a road front derailleur using a braze-on mount so any front derailleur you use will need that interface..

GRX FD "road boost" (road CL+2.5mm) may work with "non-boost mtb" cranks, but it will not work with "mtb boost" cranks

"mtb boost" > "mtb non-boost" > "road boost" > "road non-boost"

[Nikoras]

Yeah viable touring options for me right now look like.
2x GRX front with 817 rear. 30/46T with 11-42 rear
or
1x XTR rear derailleur 32T or 34T front with 11-46 rear. The only thing is with 32T seems like I would spin out on anything slightly downhill at all, and 34-46 doesn't quite hit my granny-gear target of 20 gear inches.

the 2x setup hits that range but I will have 2-3 gears with the 46 front that I probably wont use much. 1x will save weight and remove a point of failure/potential battery drain.

By the way, can anyone recommend a di2 compatible 27.2 carbon seatpost that might be good for bikepacking on rought roads?

[ooo]

You can try to fit 42/28 cranks with 11-42 cassette.
(grx fd + 42/28 or grx fd + fitlink + 40/28)

11-46 11-speed casseette is uncomfortable.

So I'm looking for a gravel/bikepacking rig which I want to use for both
day long gravel events (no intention of getting on the podium)
but more importantly long bikepacking trips.

Are you sure you need the same gearing ranges for both scenarios?
If you can find two separate gear ranges for each scenario - you can use different front chainrings for them

[Nikoras]

You can try to fit 42/28 cranks with 11-42 cassette.
(grx fd + 42/28 or grx fd + fitlink + 40/28)

11-46 11-speed casseette is uncomfortable.

So I'm looking for a gravel/bikepacking rig which I want to use for both
day long gravel events (no intention of getting on the podium)
but more importantly long bikepacking trips.

Are you sure you need the same gearing ranges for both scenarios?
If you can find two separate gear ranges for each scenario - you can use different front chainrings for them

Yes this is being revised to an N+2 scenario from when I made this thread about a year ago. I actually ended up picking up a diverge and love it and have been riding it all the time, but I kind of also want to build a cutty for an ambitious bikepacking setup.

[uquality]

If the Shimano page lists the correct information, the GRX 48/31 crankset has a special P.C.D. of 110/80mm - so even smaller than supercompact. with this chainring diameter, you could easily swap to 26/40 (heavy touring gears)...if you need it. But: smaller chainrings are not yet available, as Shimano doesn't offer them. BUT: Just had a chat with Absolute Black.



looking forward! This 48/31 crank could be a one-does-it-all! 48/31 for road/gravel - and change to 26/40 for touring.

I want to go the opposite way. I gravel race and fastpack. I'd like a 34 inner ring for tighter gearing.

Also the 815 derailleur does 36T just fine I believe.

[uquality]

I want to go the opposite way. I gravel race and fastpack. I'd like a 34 inner ring for tighter gearing.

Also the 815 derailleur does 36T just fine I believe.

I posted this and when googling and found out GRX is fully compatible with Shimano 11-speed road chainrings.
Well... that solves my issue. 34T inner rings are easy to find.

[scurran]

I want to go the opposite way. I gravel race and fastpack. I'd like a 34 inner ring for tighter gearing.

Also the 815 derailleur does 36T just fine I believe.

I posted this and when googling and found out GRX is fully compatible with Shimano 11-speed road chainrings.
Well... that solves my issue. 34T inner rings are easy to find.

I don't think this is the case, although I wish it was. I really would like to have a separate set of CX rings and gravel rings. 46/36 is what I need for CX.

It looks like the ultegra rings are mouted on the exterior of the "spider" while the GRX outer ring is mounted to the interior of the "spider". Can anyone confirm there is not a single option for 2x replacement rings for GRX? I've reached out to wickworks, praxis, absoluteblack, all crickets....

I am planning on going with easton, which seems like an ok choice, but I'd rather do GRX and get the right side (cant fit a left side PM) 4iii PM, as opposed to the cinch due to cost.

[Nikoras]

As for my build, I'm still waiting on the frame. I think it's safe to buy a race face next SL crankset as it uses the Cinch system which will play nice with any gearing choice I choose.

I'm interested in seeing if I can't bodge together a 26/36 setup using this adaptor to lower the GRX FD https://wickwerks.com/products/fit-link-adapter/ with an 11-40 rear. This would keep the jumps smaller and give me a nice gear range.

The simplest solution would be a 32T 11-46 rear 1x, but that compromises on all fronts. Big jumps, low top gear, not quite as good bottom gear. But the pro's would be peace of mind when out in the middle of nowhere knowing that nothing will go wrong as opposed to a bodged together adaptor + Front derailleur setup.

[uquality]

I don't think this is the case, although I wish it was. I really would like to have a separate set of CX rings and gravel rings. 46/36 is what I need for CX.

Damn I just did some googling and found out GRX have different BCD for front/rear as 120/80.
However, you CAN use regular road chainrings for the outer ring, they just won't match aesthetically.

I'll have to play with different cassettes rather than swapping chainrings.

[nateners]

The deciding factor in whether the mech will work is not the cage length. That has SFA to do with it. Hanger length has more to do with it.

If you’re looking to get lower gearing, why not look at a XT or XTR mech setup? I run 44/30 x 10-42 which gives me super low gearing without the top end & gearing gaps compromises 1x forces.

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So it would be possible to use GRX Di2 and an XT/XTR rear derailleur?

Would there be any complications in the drivetrain?

[TerryDi2C]

GRX shifters and XT/XTR FD + RD - yes.
GRX FD and XT/XTR RD - no.

All installed derailleurs must be from the same "category": either MTB (XT/XTR) or "road" (Ultegra, DA, GRX).

[ultimobici]

So it would be possible to use GRX Di2 and an XT/XTR rear derailleur?

Would there be any complications in the drivetrain?

If you’re using it in a 1X configuration, it’ll be fine. If you’re going 2X, you’ll need to keep the mechs matched. XT/XTR has to be used with XT/XTR, DA/Ultegra/GRX can be mixed & matched. Front mech choice on the later will depend on the chainset used. Road chain line = DA/Ultegra, GRX requires GRX. Not sure if MTB & GRX play nice together, though.


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[satanas]

Re rings: Last week I was looking at TA's website and they're now listing rings to fit GRX. The recommended combos are 48x32, 48x31, 46x30 and 44x28 - unfortunately nothing smaller yet, but 42x26 or say 38x25 ought to be possible with the GRX BCDs.

[fourfa]

44/28 with 11-36 cassette would suit me fine for loaded (and even for unloaded roadie days with 10-36)
42/26 even more flexible, as you can get a real granny with a 11-34 or 11-36, and decent roadie gears with the 3T 9-32 cassettes

(FWIW I'm using mechanical shift and 46/30 with 11-40 for short gears when I need to haul and it works - but the capacity is super maxxed. Di2 definitely safer tough as you can lock out big-big and small-small)

[satanas]

Gearing is very individual but FWIW 42x11 was mildly annoyingly low only one afternoon in 2019, when descending from Andorra into France; even then it was only an hour or two. Agreed that 26T at the front would make 34/36T at the back much more useable; maybe that might come later on. 44x11 would be plenty high enough for me 99+% of the time, and 28x34/36 should handle most things, and for steep bikepacking offroad a 13-40 cassette should be possible with a mix of Miche and Shimano cogs. Also FWIW, 42x27 + 11-40 had enough range with an Ultegra RX RD that all the gears sorta worked, not that I used 42x35/40 or 27x11/13.