Today I read an interesting article on the Gravel Cyclist website. I'm currently running on a Shimano GRX groupset with the RX810 derailleurs and 48-31T cranks. According to Shimano, the highest cassette you can run on an RX810 derailleur is 34T. But, as the Gravel Cyclist learned, you can actually run as high as a 40T cassette.
Strange timing in that I was on my way to the bike shop today to pickup a rear wheel for training. I was gonna pickup another 11-34T cassette but, after reading this article, I bought a Shimano XT CS-M8000 11-40T cassette instead.
I can confirm that, yes, this indeed does work. Like the Gravel Cyclist video explains, you have to adjust the tension using the "B screw" (as Shimano calls it). I nearly screwed up and didn't give it enough tension. Just have to be careful with it.
One tip when adjusting is to switch to the second biggest cog just before the big 40T one. That one is close to a 34T so you shouldn't have any problems. From there, adjust the tension so that there is enough room to allow for the switch to the 40T cog. Once that's done you should be able to switch with no problems.
On mine, I had to adjust the tension on the shifting cable a bit as well as a bit of adjusting the L-limit screw. I might have to tweak some things but going back and forth between wheel sets should be just a matter of adjusting the tension a bit. Even then, I might be able to get away with going back and forth between 11-34T and 11-40T cassettes without adjusting anything. Just have to dial it in a bit I think.
Very pleased to hear this! Means I can run my 700c gravel wheelset with better low-end gears. Nice!
Post a comment!
Hi, did someone test with success the following GRX drivetrain : 46/30 or 48/31 + RD812 + 11-42 cassette ?
This video might help with that answer:
Excellent writeup -- seems the wealth of information out there on this topic isn't so much in the Gravel Cyclist video (not that it's bad -- GC did a great job!) so much as a lot of the operating experience coming from folks giving it a try after watching it.
So I too am in the situation of wanting to keep an 11-34t on my 700c wheels for road cycling, but for my 650b wheels with the hefty 2.1" tires for the gravel days, I've purchased an 11-40t. I keep chickening out of playing around with this setup based on not wanting to compromise my road shifting with the excess chain length.
Would you be willing to share your experiences swapping between wheels with different cassette sizes? I'm thinking that if the cassettes are close enough in left-right alignment, the only adjustment would be the B-screw (and possibly a microtweak to the cable tension if it's reluctant to hop up to the 40t). Is this the case? Also, since you now have a slight excess of chain when running the 11-34t, how's the shifting when running that cassette?
Curious as to your thoughts and experiences,
Honestly, on my gravel bike, I decided to keep both my wheelsets (knobbies and semi-slicks) set with 11-40t cassettes. Just makes it easier in the longrun and I don't have to worry about the slack on the chain. The difference between an 11-34t and 11-40t isn't that bad on my gravel bike. For my road bike though, I stuck with an 11-34t on that one.
I changed the front to 30/46 And the cassette to 11-40. It works perfect with my Shimano GRX 810 and Ultegra FD-R8000. I had to change the chain for a longer one.
I really enjoy the granny gear for climbing here in the alps. Thank you!
I was thrilled to see an article addressing the limits of what this system can do. However, I do have a question. Even though I have a GRX groupset, I spend a fair amount on the road. I have a 2x10 (grx600 and mostly 400 combo). I changed the original 46T for a 48T from the 800 system, But I feel like I could do with a couple more teeth at the front. Do you think the system can cope with a 50T, likely changing the smaller front sprocket to stay within the suggested maximum difference in teeth?
I can't say I can give you the correct answer...but I would imagine using a 50T is ok. Use a gear ratio calculator to see what the difference is. Main thing to me that would be critical is making sure you use the correct chain length. Might need to add some links.
Hello. Going the other way, what about a smaller range cassette? Shimano states the low sprocket min is 30T for the RD-RX815. Would like to use the 11-28 cassette for road rides. Not sure what the reasoning is for this but any idea if it would work? I have the 48-31 crankset.
Hey Bob, sorry about the delayed response. I don't have a verified answer but my guess is that it should still technically work. If the minimum is 30T, I don't see why a couple teeth down wouldn't work. Main thing I would think you'd need to pay attention to is the number of links on the chain used. That and adjust the tension on the rear derailleur.
I can verify it still runs smooth with a 11-23 with the same chane I use on 11-34.
Thanks for your review...I'm looking at doing the same thing with my GRX 810 and adding an 11-40t cassette. Is yours mechanical or Di2? I think I'm going to add the Wolftooth Roadlink as an extra measure so that I don't rip anything in big/big since I'm running mechanical instead of Di2.
My pleasure! :)
Mine is the mechanical. Not sure if this hack will work with the Di2 version. If the specs are the same, I can't imagine it not working. I also thought about that Wolftooth cog but decided against it.
Wolf Tooth updated their discription for the RoadLink DM and recommend it for the Grx 810.
Ah good to know! Thx for the update! :D
Great and very helpful article, answering the question I've long had: Is it possible to run a rear cassette with more than 34T with a GRX 2x11 crank? This clear, simple answer is super -- much easier than searching through other sites. Thanks!
Your welcome! Thanks for reading! :D
I assume this will also work with 50/34 chainrings because the derailleur has to make up the 16 tooth difference, which is less than your 48/31 (17)? I will just have to adjust chain length?
Technically, yes. Main thing is setting the chain length to accomodate both the 40T in the back and 50T in the front. Basically, the rear derailleur doesn't care what's up front so long as you have the correct chain length. That said, you probably won't want to be running your bike with 40T and 50T engaged at the same time. That's a serious cross chaining issue and isn't at all recommended with this hack. I don't ever go beyond 3rd gear much less 2nd when in the largest chainring. Just not worth the wear and tear it places on the cassette and rear derailleur. I can feel it too so I just downshift into the smaller chainring as needed.
Thanks for this Jeff. I am tinkering with mine as we speak upgrading from 9s to 11s setup. Almost got for myself the 11-42t cassette but changed it to 11-40t after reading this. Will see how it goes after the installation this week. Hopefully no issues. I am pairing it with GRX 810 RD and GRX 810 FD and 48-31t in front.
Might be late to the party... I have Salsa Fargo Tiagra which has MTB front 26-36 and Shimano CS-HG500, 11-34t in the back. As far as I managed to research, 11 speed GRX810 is comaptible with 10 speed Tiagra shifters. I would like to upgrade to 11-42 in the back. According to my calculations this idea demands chainring capacity of 41 and official GRX810 capacity is 40T. So, what is your opinion, would this work? Would I need longer chain? Thank you for your response!
42T cassette in the back might not work. The reason is that the derailleur needs room to clear. A 40T works and still has just enough room to clear. 42T might clear...but just barely. At that point, the problem is then a matter of chain wear. Switching to the 42T could potentially cause excess chain wear due to the stress being added when switched to the 42T gear. I would err on the side of caution and stick with a 40T. You could change the size of your front chainrings to accommodate going from a 42T to a 40T. 24-34 maybe?
Chain length is kind of a separate thing really. It's dependent on the combination of the cassette, front chainring, and chainstay length. I use an app to calculate the chain length but online ones like this work just as well:
Grx 2x with 11-42 works beautifully
Would RD-RX400 work too (although it's 2x10) to use it with 11-40T cassette? RD-RX400 supports up to 36T cassette and uses same 11-speed technology in the rear derailleur
Sorry for the late reply. Thats a good question. Honestly, I can't really answer that question. Technically, the RX400 is very similar...but I can't say it has the same wiggle room as the RX810. You could try it...but be very careful. Definitely don't want to push it further than it's capable of.
At the end I managed to get RD-RX400 with CS-M41000 (11-42) cassette (clutch on), works like a charm. I use 2x10 GRX (crankset 46/30T and levers ST-RX400). I wouldn't use the 46 chainring with the 37 and 42 sprockets btw, it extends the rear derailleur too much.
That is awesome! Thanks for taking the time to document this. Good to know that there are ways to stretch the capabilities of even an RX400. :D
Why are shimano, sram, and others so afraid to give us factory spec ultralow gearing with road mech? GRX is a step in the right direction but still not enough for any serious work.
Good points and certainly something to think about. With the GRX line, Shimano would rather spec them with a range they know to be super consistent and safe rather than the absolute max. Technically, running a 40T cassette with a GRX derailler is pushing it a bit...but it does work, right?
That said, what I see happening with ultra low gearing is a push to create gravel bikes that use more mountain bike components: wider bottom bracket, more tire clearance, and a drivetrain that allows for even lower gearing. A good example of this would be the Kona Sutra ULTD. It's still a dropbar bike but with more of a mountain bike thing going.
Does it have to be the hyperglide version or can I run a normal XT CS-M 8000 cassette (half the price)?
You can get away with using a cheaper cassette. Come to think of it, I dont think even I use the Hyperglide cassettes. I use a Shimano XT M8000 (11-40T) which is likely to be the exact same cassette you referenced. :P
Which GRX 810 RD? Medium or Long-cage? Thanks.
This is for the RD-RX810, which is a medium cage derailleur and technically can accept between a 30-34T cassette. The RD-RX812 has a larger cage and can accept between a 40-42T cassette. My understanding is that the RX812 is primarily for a 1x11 drivetrain and doesn't work so well with a 2x11 setup. It might be possible to use it in a 2x but your mileage might vary in terms of getting it to work with the higher gearing (ie. 31x11t). That's why the RX810 hack is so valuable. With the medium cage, you can insure that all gear work well without risk of having too much chain slack.
I live in Barcelona Spain and just bought a Specialized Diverge Carbon Comp. The 11-34 rear cassette was good but there are some real hills here and at 61 they can prove to be a challenge. I saw your video and read the article. I ordered the 11-40 cassette and installed it last week. It works flawlessly with the stock chain. I just readjusted the B screw and it was set. Shifts like the stock unit. Thanks for the great tip.
Thanks for the compliment, Mike! Glad the video and article helped! :D
I have the same bike and just ordered the cassette. Did you need a spacer for the cassette? Thanks
I do have a single spacer on the cassette. It's not really needed I dont think but having it there does help make it easier to adjust the rear derailleur. Try without one and see if it works. If you have a hard time getting the low limit set right then, yeah, adding a spacer will help.
This is great information. Thanks.
I just bought a GRX810 equipped Cervelo Aspero and, based on calculations, I know the 31f/34r granny is going to be lacking when it comes to some of the long climbs around here. I had planned on picking up an 11-40 XT cassette, so it's good to see it will work without needing to add something like a Wolf Tooth extender on the hanger.
Thanks for the comment, Brent! :)
Yeah, I've looked at the Wolf Tooth extender and I'm not sure it would even work with an RX810 rear derailleur. Looks a bit too short...or is it just me? :P
WolfTooth makes two different versions, the RoadLink and the GoatLink for mtb (and probably gravel?). I've used the shorter RoadLink to take my vintage road bike (with Campagnolo Super Record rear derailleur) from a 13-18 freewheel up to a 14-30 for Granfondos that have long, steep, climbs. I'm guessing (without looking into it, yet) that the GoatLink would allow an even larger mtb cassette to be used on a gravel bike. It would be fun to experiment with it.
This is a wonderful post to find, thank you! I've been down the rabbit hole for days! Do you know if the GRX derailleurs will work with a White Industries G30 crankset and VBC 2x chainrings? I am hoping to get a 46/28 up front and 11-40 in the rear. I'm a big dude, on heavy steel bikes and looking for the widest 2x I can muster.
Thanks for the compliment! Much appreciated! :)
Honestly, I think that's a question for White Industries. Only thing I think could be problem is the width of the crankset. The G30 requires a 68/86mm bottom bracket whereas the GRX cranksets are set to 38mm. That might be an issue for the front derailleur. If it can be spaced out a bit so that it lines up right though then the only other issue would be the spacing of the chainrings and overall compatibility which if they're truly Shimano compatible then it won't be much of an issue. But my first guess would be that the spacing issue would likely be the main thing with this application.
I will say that Shimano did a good job in making sure that all of the GRX components are cross compatible with other Shimano parts. For instance, I'm using 105 levers with the GRX 2x front and rear derailleurs with no problems. But that's not to say that third-party stuff will work. I think as along as its Shimano compatible I don't think you'll have issues. Best to ask the manufacturer just in case.
Hi Jeff! Awesome post! Same as the previous comment my chainring is an 46/30. But my RD is GRX810. So I am assuming this would work the same as yours? Another question is, did you have to change your chainset to accommodate the 11-40 cassette?
Thanks for the compliment! Mucho appreciated! As for your questions...
A 46/30 crankset should work so long as it's compatible. Most of the current Shimano-compatible cranksets should work. If it's a Shimano specific crankset, take a look at the Shimano Compatibility charts for the rear drivetrain just to be sure:
Now, provided they are compatible, a 46/30 should work. I'm using a 48/31 which isn't much bigger. It's the larger chainring that needs to be kept in check. Any bigger than a 48T chainring and you'll have to limit your cassette size significantly.
That said, you shouldn't have any problems using an 11-40 cassette. In fact, with a 46T chainring, I would think it would be easier. Main thing is to make sure to adjust the B screw so that the top pulley wheel is a good distance from the largest cog when in that bottom most gear. Mine is all the way out as far as it can go. Start there and bring it in as needed. Don't want risk locking it up. :P
One last tip. Adjust your chain length as needed. I used an app called Chainring to figure out the length. It'll make it easier to calculate the length based on the gear ratio, chainstay length, and a few other measurements on your bike. Mine ended up being 112 link so I just needed to take out two links. Helps eliminate unneeded slack and improves shifting.
Happy cycling! :)
Thanks for the tip! I'll use that as a starting point. The reason I looked up for this is that I have two wheelsets now. One still without a cassette cos I am thinking of using the 11-34T as my road cassette and install an 11-40T on my gravel wheelset. I usually go gravelling at least once every fortnight so I was thinking if its worth the trouble of tinkering with the RD adjustments every time I swap wheels. Otherwise, I'll just put the same cassette on both wheelset. But when you said you "might be able to get away with going back and forth between 11-34T and 11-40T cassettes without adjusting anything", it encourages me to try the same. :) Thanks again!
That's exactly what I'm doing. I have 4 wheelsets actually: one for indoor training, one for road, a 650b for gravel and road, and a 700c gravel wheelset. The later two have 11-40T cassettes and the inddor and road ones have 11-34T cassettes. Really gives me a solid range. :D
So happy to have found this - i looked hours for this! Now my question is: would the 11-40 work as well with the GRX 600 setup with a 30/46 chainring instead of a 31/48 chainring? Thanks!
You know, this might actually be possible with the GRX 600 derailleur. Looking at the specs for the RX400 rear derailleur (https://bike.shimano.com/en-US/product/component/grx-10-speed/RD-RX400.html) it looks like it has a bit better capacity that even the RX810. You could probably overload it with a 40T cassette. However, I would take off the chain to do it and be super careful on how close the cogs are. Otherwise, you run the risk of cogs rubbing up against one another and ruining both your derailleur and your cassette. There needs to be enough room between the largest cog in the cassette and the top cog on the derailleur so that the chain can easily pass through. Otherwise it won’t work. You could pickup a cassette and try it out. If it doesn’t work you can always just return the cassette. Just be careful and you’ll be ok. Never hurts to try things.
On the grx 600 upgrade from 11-40t, did it work?
What cassette did you use? Planning to do also but im hesitant as i dont want to make a mistake. Im planning to upgrade both chain ring and cassette and end up to have 46t and 11-40t cassette. .
Hi Sir Jeff, do you think the target new setup will be better than the my current? What are your thoughts? Thanks!
As with anything, I think the answer is: It depends.
Sounds like you're going for a 1x setup, which can be quite advantageous for gravel bikes. But it depends on how you ride. You can get a decent range of gearing even with a 1x setup but loose some of the variety you get with a 2x setup. A 46t should provide a decent range though with a 11-40t cassette. Just check some of the various chainring calculators so that you can see the gear ratios provided and compare them to the ones you're used to.
Can you go big big with your setup ? 48x40 ?
If yes does the small small is still good ? 31x11?
Not sure I understand the question. I'm assuming you're referring to a 48/40 crankset, right? If so, I don't see why you couldn't go with a 11x31 cassette in the back. Minimum for a RX810 derailleur is 30T so no problem.
I think Martin was referring to the "big/big" & "small/small" chainring/cassette combinations that one occasionally must be careful of avoiding....
Are there any issues with using the big (48t) chainring with the largest cassette cog (40t)?
Are there any issues with using the small (31t) chainring with the largest cassette cog (11t)?
Based on my understanding, there shouldn't be any issues running a 48T or 31T in those configurations. Main thing to watch out for is chain length.