Has anyone tried the Shimano GRX RD-RX400 rear derailleur with an 11-42 cassette? I am currently running a 1x11 using Ultegra 6800 shifters and rear derailleur with a WolfTooth Road Link and an 11 speed 11-42 MTB cassette (w/ 42T front chainring). It has trouble dropping into the 11 tooth ring sometimes while riding, so I am looking for a setup that doesn't rely on the Road link. I know the GRX RD-RX400 is only rated to 36T max, and the GRX RD-RX812 is for 42; but shimano is very conservative with capacity, so I am guessing it would work, and be a less expensive option. I also know that the RD-RX400 is sold as a 2x10, but it uses the same cable pull as 11 speed (like the older Tiagra group before it).
I like shopping for clearance and used stuff, but this is one place where I think I'd just spend the money and do it right. I've found that what works on one bike, doesn't necessarily work on every bike when maxing the capacity of a rear derailleur.
I went ahead and bought the Shimano GRX RD-RX400 rear derailleur. I have heard that the RD-RX810, which is rated for 34 max works well with an 11-40 cassette. I am hoping that the GRX RD-RX400 (which is rated for a 36 max) will clear the 11-42. Will report back once it arrives and I install.
Shimano is conservative sometimes... But I recently setup a GRX 812 on a 11-46 per a request. The GRX 812 is spec’d By Shimano for 11-42 max, but some have stretched it to 11-46. The issue we ran into is the B screw is so far ‘in’ to get it to shift the 46, it shifts poorly in the lower 2 cogs. He was willing to accept 2 sloppy gears to get a 46T bailout. Personally I’m doing just the 42T (Shimano recommend max) as I can’t deal with sloppy shifting.
I installed the Shimano RD-RX400 today with the ST-6800 shifters and the 11 speed 11-42t cassette (1x setup w/ 42t front chainring). It shifts through the whole cassette with b-tension screw almost all the way to its max. It easily clears the 42t cog on the cassette.
So far it shifts a bit rough at either the low end or the high end depending on adjustment. Time will tell if it is better than the RD-6800 derailleur and Wolf Tooth road link, which had the same issue with the 11-42 cassette.
It definitely shifts worse with the the clutch on than with it off.
So, I don't recommend it for the 11-42 cassette, but it would be a decent budget solution for either a 11-36 or 11-40 cassette with existing 11 speed shifters.
The GRX 400 shifters (just like the latest versions of Tiagra) use 11 speed technology in the rear derailleurs, but just pull more cable to shift to ten speed (than Shimano's 11 speed shifters do). Therefore the 10 speed Tiagra and GRX 400 can use 11 speed rear derailleurs and vice versa. But it's not officially supported.
Where did you see the RX400 cable pull is the same as 11 speed? That's not reflected in the Shimano compatibility chart (unless I'm reading them wrong)..
My long term review of the Shimano GRX RD-RX400 rear derailleur with an 11 sp 11-42 cassette using Ultegra 6800 11 speed shifters: It works great! After a few long gravel/ MTB and road rides, it is shifting great! Much better than the 11 sp Ultegra RD-6800 with Wolf Tooth Road Link. I would say that it is definitely worth the $63.00 https://www.jensonusa.com/Shimano-GRX-RD-RX400-Rear-Derailleur
Erik_A wrote:I have heard that the RD-RX810, which is rated for 34 max works well with an 11-40 cassette.
I wrote more in depth somewhere else (and need to edit it), but I have had pretty good luck with the RX810 with the 11-40 and even the 10-42. The entire range of the 11-40 is flawless. The Roadlink DM made the shifting between the 36 and 42 (on the 10-42) cassette super smooth, but left a lot to be desired between the 10 and 12. I ended up ditching the Roadlink DM and going back to the stock guide pulley to get relatively good shifting at both ends. Sometimes it hesitates going from 12 to 10 and occasionally I hear some rumble going from the 42 to 36, but I'm pretty happy. Typically if I'm shifting off the 42, it's multiple gears since I just crested something so that's sort of a non-factor.
I threw an 11-42 from my wife's bike on without any adjustments and it shifts slightly better on each end (in the stand), so that's a good choice if a bit less top end is needed.
After a few more months of almost daily use, the Shimano GRX RD-RX400 rear derailleur with an 11 sp 11-42 cassette using Ultegra 6800 11 speed shifters is working flawlessly. No RoadLink etc, all stock. I do turn the clutch to "off" though. The only negative, which is minor is that cage on the RD-RX400 is super long. It shifts well, but the looks a bit strange to my eye on a bike with drop bars and gravel size tires. I think that the more expensive RD-RX810 with the shorter cage would look better.
@Erik_A can you please explain why it's possible to use a 10-speed derailleur with an 11-speed cassette? I'm a novice and didn't realize this was an option. I'm using my stock RD-R7000 (105) derailleur with a Sunrace 11-42 cassette (no roadlink, 46/32 in front) and might be interested to see if your GRX RD-RX400 shifts better. It's fine in the lower gears, just a bit rough in the highest gears and I'm wondering if the longer cage would fix that...
Mark- Because the GRX 10 speed shifters are using the 11 speed RD tech. They won't work with typical 10 speed RDs. Just like the last version of Tiagra 10 sp.
Thanks for responding Erik. Just to confirm as well - it doesn't matter that I'd be using this as 2x11? The capacity of 41T is better than my current 39T with the RD-R7000-GS so I have to guess it would be fine.
Mark- I am using an 11-42 and it works great, so a 41 should be even better.
Mark_S wrote:Thanks for responding Erik. Just to confirm as well - it doesn't matter that I'd be using this as 2x11? The capacity of 41T is better than my current 39T with the RD-R7000-GS so I have to guess it would be fine.
Thanks Erik - I actually have an 11-40 cassette, so even easier to reach. But what I'm wondering is whether there's any reason I will not be able to use the GRX RD-RX400with a 2x setup (meaning front derailleur and double chainrings)? If not, then this is brilliant and I'd never have noticed this derailleur option as Shimano markets it for 10s.
You said Ultegra 6800 11 speed shifters with RD-RX400, I ask ST-RX400-R 10 speed lever with RD-RX400 - all 10 speed? Front 1x42 rear 11-42T cassette 10 speed. Think will be ok, but need to know.
No RD-RX400 will not work with 10 speed shifters other than 10 sp GRX 400 and the new 10 sp Tiagra.
borxes wrote:You said Ultegra 6800 11 speed shifters with RD-RX400, I ask ST-RX400-R 10 speed lever with RD-RX400 - all 10 speed? Front 1x42 rear 11-42T cassette 10 speed. Think will be ok, but need to know.
