Bikepacking gearing with GRX Di2

[Nikoras]

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. My current contenders are the Specialized Diverge and the Salsa Cuttthroat.

To get right to the point the Di2 version of the Cutthroat looks most appealing but a 30/34 is simply not enough granny gear for loaded up Vermont singletrack. Is there any way to run a 28 or Ideally 25T inner chainring with the Di2 GRX groupset?

In terms of the overall bike choice I realize the diverge and the cutthroat are very different bikes, but the SRAM AXS mullet build on the diverge gives would give me a nice range (36/50 granny), 47mm tire clearence is actually on the high end for gravel racers that can be used for bikepacking. The downtube storage is a nice little bonus. The futureshock is welcome for the day rides (I imagine it will compress when loaded with a frontloader but with the lockout that's fine). Also it has a threaded BB!

On the otherhand the salsa Cutthroat can run all the way up to 2.35 in tires which would be nice for the singletrack. I'm not sure how I would get on with the geometry being that short, but I would have to trust the experts who seem fine with it for long bikepacking epics. The Cutthroat is quite a bit slacker, not sure how I feel about it. My main concern about going with this bike would be achieving the gear ratio needed for bikepacking. If you look at Tour Divide rigs they all run in the realm of 25/34 granny for 2x and 32-36/46-50 for 1x. Talking to the folks over on reddit's bikepacking forum this seems to be the prefered gearing for any loaded up offroad multiday adventures.

[Nikoras]

Just some further thoughts, if my ultimate goal is to ride the Tour Divide, how much would I be handicapping myself on a Diverge with 47mm tires vs A cutthroat with a much more stable geometry and 2.35 in tires?

[pdlpsher1]

You want more gearing and yes, it's very annoying Shimano decided not to offer super-low gearing. But fear not you can make a modification to the GRX RD by using a long cage (SGS). Then you can run 11-40, 11-42, or 11-46 cassette on the back. Open the video link and expand the video description. Good luck.

https://www.youtube.com/watch?v=7kUxmkuJWNg

Content of this video:
The original RX812 rear shifting inner and outer plate are changed to the XT RD-M8000-SGS super long cage rear derailleur to support the front double-speed crank, and further support the rear derailleur to 11-46T. (The results will are like the attached video)
.
The following parts are testing in the video:
1. FC-6800 50-34T
2. CS-M8000 11-46T
3. FD-5800
4. RD-RX812 w/RD-M8000-SGS plates
5. CN-HG701

Required parts.
1. Shimano GRX RD-RX812 1x11 speed rear derailleur x1.
2. Shimano XT RD-M8000-SGS Outer Plate x1.
3. Shimano XT RD-M8000-SGS Inter Plate x1.

[Nikoras]

Hmmm a bit scary to try that hack. It's a shame Salsa did away with the Force 1 specc'd cutthroat. So many "could'ves" Shimano could have offered bikepacking friendly gears on GRX, Salsa could have specced a SRAM mullet build or at least kept the force 1 2019 spec.

I'm leaning towards the Diverge right now for a few reasons A.) The geometry looks favorable (The cutty would take a lot of tinkering with those stem/reach stats). B.) The gearing and is reaaaally nice on the pro model with mullet build. C.) it would probably be a little more fun on the local gravel rides to get my feet wet.

The drawbacks would be, limited singletrack due to limited tire width (compared to the Cutty) and I would likely have to put my tour Divide dreams on hold.

So the plan would be get the Diverge and get the bikepacking setup. Then see how I get on with it and re-visit my dreams of doing the tour Divide a year from now. The only problem I see with this plan is I have a 6 week sabbatical from work available to me now, and if the plan is 2 years out my work might not be around by then. We are a small pharma company in the clinic and I could see us getting bought out or going under (depending how the drugs do). Though I guess the former isn't a problem as I would be in a better financial spot.

[justaute]

Maybe I'm missing something. Thought I had read the GRX Di2 can easily run a cassette up to 40T.

[Nikoras]

Hmm? I'm looking for easier gearing. So something like the SRAM mullet's 36-50 1x is ideal for a 2x a 25-34 would be ideal as well. From what I'm reading for bikepacking in particular you really want gearing on par with a true MTB setup. If I were to go with the cutthroat that means I would definitely want it focused towards the bikepacking end of things. The cutthroat is the bike that comes with GRX. If I were to go with the diverge I could simply swap the front chainring and be good.

[justaute]

Hmm? I'm looking for easier gearing. So something like the SRAM mullet's 36-50 1x is ideal for a 2x a 25-34 would be ideal as well. From what I'm reading for bikepacking in particular you really want gearing on par with a true MTB setup. If I were to go with the cutthroat that means I would definitely want it focused towards the bikepacking end of things. The cutthroat is the bike that comes with GRX. If I were to go with the diverge I could simply swap the front chainring and be good.

Ahhhh...I just thought if you were to go with GRX Di2, you could get a 11-40 cassette as it should be able to handle it and thus give you easier gearing.

[pdlpsher1]

GRX RX-812 can handle a 11-42 but only on a 1x because it has a mid-cage. GRX RX-815 has a long-cage but it can only handle a 11-34. You can run a RX-815 with a 11-40 but the upper pulley will be very far from the smaller cogs, so shifting will be marginal on the higher gears. The RX-815 isn't designed to follow the arcs of a 11-40 or 11-42. The best option for low gearing is a RX-812 modifed with a long-cage, and pair it with a FD for a 2x setup. The RX-812's geometry is designed specifically for a 11-40 or a 11-42. The modified RX-812 will give you 2x capability along with a 11-40 or 11-42.

[justaute]

This review has quite a bit of info.
https://gravelcyclist.com/videos/shiman ... that-good/

[tomh79]

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.

[Nikoras]

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.

Wow very encouraging! I also came across this https://www.youtube.com/watch?v=sRgLG1uP_uo you can basically get a 30-40 granny out of the box or replace the deraillur hanger and get it working a little better, that starts to push it into the range of acceptability for me. With those two pieces of info I'm definitely leaning back towards the Cutthroat. It might not be as thrilling on the local gravel rides and the position will take some work to get dialed, but it does seem significantly more capable than the diverge for touring/bikepacking.

[justaute]

Here's another video for you. https://www.youtube.com/watch?v=wNeYYM9_aeM

[Nikoras]

I do wonder how it would do overtime though. It looks like there might be some strain on that derailleur and the last thing I would want on the Tour Divide is for that thing to crap out on me in the middle of New Mexico.

[ultimobici]

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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[Nikoras]

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.