Atlas Shrugged

For reference I am building up a new adventure bike and wanted a wider range that was offered by stock GRX 2X systems. On this bike I have a 48-31 front chainrings and 11-40 rear cassette and it works brilliantly. I took a standard RD-810 rear derailleur and mounted a wolf tooth road link dm for extra clearance and also replaced the pulley cage with one from a XT mid range. It works and shifts perfectly with sufficient capacity to go from small-small to big-big without issues. It is clear that it would handle a 11-42 without problems as well. Just for reference if anyone is interested in increasing the range in their GRX bikes without any compromises.

SoSmellyAir

Did you retain the GRX pulleys or use those from the XT cage? I ask because the GRX has a bigger than usual 13T tension pulley.

Atlas Shrugged

I used he XT pulley wheels however it looked like it would fit just it would be very tight.

Polaris OBark

I now have an SLX 11-40T cassette on my touring bike with a GRX 46/30T crankset and GRX derailleurs. A small adjustment of the B-screw was all that was needed. I suspect I could have used an 11-42T cassette, but I didn't want to push my luck.

This makes the gearing viable for a fully-loaded touring bike. I took it for a loaded test ride today, and hopefully will have an extensive real-world test soon.

SoSmellyAir

Are you also using a Wolf Tooth road link (like Atlas Shrugged)? Which GRX RD are you using: (a) RD-RX810 (for 2x front) or (b) RD-RX812 (for 1x front)?

Polaris OBark

No Road Link. Just a standard GRX 2X setup, with RD-RX810, and a turn of the B-screw.

I tried it after seeing this:

https://velonut.com/blog/shimano-grx...1-40t-cassette

which references this:

https://www.gravelcyclist.com/videos...-xtr-cassette/

SoSmellyAir

Great information. Thank you for linking. Good to know there are additional options if a 34T cog would not get me up a climb.

Is the big-big combo viable if you install a longer chain?

Polaris OBark

I had a 36T cassette on there for a few years. Shimano's 34T limit is excessively conservative.

FWIW, I also use a 36T cassette with my 2014 Ultegra derailleur rated at 32T with zero issues (again, just a B-screw adjustment).

SoSmellyAir

I also knew the 34T limit was too conservative and that a 11-36 would most likely work but fitting a 11-40 into a 2x GRX drivetrain is a game changer.

I request a moderator to make this thread a sticky in the gravel sub-forum.

Polaris OBark

I used the whole of the 116 link chain. Big-big works on the stand. I haven't tired it under load, but I would only go there due to a shifting error.

SoSmellyAir

I have 3 Ultegra chains in reserve and all 3 are marked 126L; I wonder if I can go 11-42? Too much chain slack for the RD to take up?

I get why we should avoid big-big (i.e., noise and wear) but why would it work on the stand but not under load?

Polaris OBark

It will probably be fine. I somehow missed your question and was just answering it as accurately as possible. I haven't tried it under load.

Atlas Shrugged

Have run big-big a numerous times under full load and no issues. It works good without the mods but notice it’s just not right. Once I put WolfTooth and swapped cages it shifts like factory across full range. Since I use mine for extended tours rather not stress the system. I also run 11-42 as well for some trips no issues.

HTupolev

This is a very common sort of gravel drivetrain in my area. RD-RX400 or RD-RX810 paired to a cassette with a 40+ sprocket on some manner of subcompact double crank.

SoSmellyAir

OK, gang, I have ordered an 11-speed XT 11-40 cassette for my GRX 2x drivetrain.

Sierra_rider

I too am running the slx 11-40T rear cassette without the Wolf link and with a GRX 810 2x set up. Minor adjustment of the B-screw was all that was needed.

I really like the set up, I ride the gravel bike on quite a bit of terrain that would be better served with my XC mtb, so the 31-34 combo wasn't quite cutting it on some of the double-digit offroad climbs. I really liked the stock gearing everywhere else and was worried that the 11-40 would be too gappy, but that hasn't been the case. I don't use the 40t often, but it's really handy when I do use it.

Kinda O/T, but I've even managed to get the 11-40 on the back of my road bike with the use of a Wolf link, derailleur is an Ultegra GS 8000 mechanical. It worked quite well, I only put it on once for a local century that included 14k' of climbing.

SoSmellyAir

11-34: 11, 13, 15, 17, 19, 21, 23, 25, 27, 30, 34
11-40: 11, 13, 15, 17, 19, 21, 24, 27, 31, 35, 40

One reason I plan to make the switch is because I don't think I need two gears between the 21T and 27T cogs.

t2p

have one 1x bike with a 10-42 - the gaps are little issue … with maybe one exception : the 10 to 12 gap is fairly noticeable …

certainly less than the gap to / from the 48/31 chainring shifts on my 2x gravel bike

did not think I would like 1x but it grew on me quickly … not for everyone / all conditions of course

SoSmellyAir

I am pretty sensitive to gaps when road riding, having switched my 11-speed cassette from 11-32 (came with bike) to 12-25 (no bailout gear) then to 12-28 (Goldilocks), all with 50/34 chain rings. So I was pleasantly surprised that this sensitivity did not carry over onto riding my gravel bike. 11-34 has worked pretty well with my GRX 48/31 chain rings, but now that an 11-40 XT cassette is available for a semi-reasonable price, I picked one up in anticipation of graduating to more challenging terrain later this year.

SoSmellyAir

The diagram on the side of the box is confusing; I will still need to install the 1.85 mm spacer behind the 11-40 cassette, right?

Polaris OBark

If you have a 10-speed free-hub (which is a 10/11 speed mtn free-hub), you do not need a spacer.

If you have an 11-speed road hub (which I assume is what you have, based on what you describe above), you will need a 1.85 mm spacer. (The spacer makes it look like a mtn free-hub).

Troul 

i've had mixed thoughts from lbs in running 50/34 with a 11-36 cassette. None suggested 52/36 with 11-36 cassette. I have not looked further into those two setups, but it would be something I'd go with at a later date... I'd just have to do more investigation. The Shimano Hollowtech II crank options do offer both the 50/34 & 52/36, but only shows the 50/34 being used with a 11-34 cassette. I'm assuming the rear der is a mid length cage at best, limiting to the 11-34t.

SoSmellyAir

1. Do you really need the 52:11 ratio?
2. We are talking about a GRX rear derailleur (i.e., RD-RX810) for a 2x gravel drive train here. Compared to a medium-cage road RD (e.g., RD-R8000-GS), while both have a max low sprocket of 34T, the GRX has a slightly greater total capacity (40T) than the road RD (39T). Plus a GRX drive train is usually paired with a 48T or a 46T big chain ring, rather than the 50T or 52T chain rings in a road drive train.

Troul 

given what limited knowledge I have, the parts will likely be: Shimano mech 105 RD-R7100, 11-36T cassette, 105 FC-R7000 50/34 (compact) . If going with a 52/36 is not out of range with the aforementioned rear der & cassette, then the 52/36 will move in the place of the 50/34.