Gravel Cyclist: Shimano GRX 2x with 11-40T Cassette

by Jeff Whitfield on | 15 Comments

Articles Tips Gravel

11-40T cassette with a Shimano RX-810 rear derailleur

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!  

Read the Gravel Cyclist article

Post a comment!


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


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


Hi there

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 ( 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.