mschwett 

i went with an SRAM XD 10-42 cassette with my GRX 812 RD (1x setup) in order to run a smaller ring up front and still maintain some top end. the GRX is spec'd for 11t min but it works flawlessly on the 10-42. you could then go down a couple teeth up front. there's a pretty wide price range for those cassettes, but lots of choices.

t2p

(if this was mentioned above I missed it and apologize)

the 812 RD might also have a ‘clutch’ - if so you might find this feature to be an asset ... adds some weight - but could / should reduce (eliminate?) chain slap ... also possibly to help keep chain on (?) ...

t2p

need XD Drive freehub to install XD 10-42 - correct ?

(I have XD 10-42 - mounted on a XD Drive freehub)

mschwett 

yes. was about $70 or so iirc.

SoSmellyAir

The GRX 810 crank and the GRX 600 crank are both 110/80 BCD, so theoretically should fit. However, the 48T chain ring that comes with the GRX 810 crank is a Hollowgram chain ring and might thus be thicker, as you mentioned. I don't really care about appearance, but of course I do not want to mess up the chain line or the shifting. So perhaps 4 thin spacers would be necessary; that is a worry for the future.

Eric F 

I’ll keep that in mind, but I’m not confident that I can get an XD freehub for my wheels (American Classic).

Eric F 

The 812 does have a clutch.

Fentuz

There are still some places with some stock
https://clee-cycles.co.uk/P4802/product

If you are going for XD or XDR free hub body, you might want to consider a e13 9-46 cassette. They work with Rival1 (and a 12s Sram eagle chain on 11s cassette) and are better with shimano.

t2p

pics of the 810 (top) and 600 (bottom) cranks

can see the difference in the chainring thickness near the mounting area / holes - and how the chainring arm mounts down into the machined recess in the chainring

810 is a much higher quality crank - including the big chainring

600 crank is marketed as 105 level and often described in this manner (possibly also by Shimano?) - but it’s a significant step down from the 810 and is more similar to Tiagra level imo

msu2001la

Thanks for posting this. I also have a GRX 812 and have been wondering if I could run a 10T SRAM cassette on an XD Driver.

Looking at SRAM's website, am I correct that the only 11sp cassete they make with the 10t cog is the 10-42? I am hoping to find something like a 10-32 that would still have the 11t cog.

Eric F 

Thanks for the info.

jonathanf2

Eric since you're going with a GRX 812, I'd highly recommend at least going 11-46t on the cassette. The 812 RD can definitely handle it. Also I'd make sure to adjust clutch tension. I loosened my 812 clutch just enough where I can keep it ON all the time, without affecting shifting. With a 38:46t gear ratio of .83, I consider that the bare minimum to tackle the local climbs in the area, even then you'll be wishing you had an additional bailout gear.

If you want to push it, the 812 RD with a Goatlink and 11-50t isn't bad. The only issue I've encountered is having to exert slightly more effort shifting from the 11t cog. It'll also allow you to step up your front chainring size to a 40/42t.

mschwett 

yep. lots of different versions of it but they're all 10-42. these are definitely more about range than small steps.

there's a crazy e13 one that has an 11t... but it's 9t, 11t, 13t, etc. 9-46. probably too much for the 812 anyway. garbaruk does 10-46, also 10, 12, 14 etc. sunrace as a 10-42 like SRAMs, but very heavy.

Symox

Just got a bike with the excellent microshift Advent X drivetrain. I changed the chainring to a 32T oval. Combined with the microshift 11-48 cassette it is perfect for the climbing I do. Sometimes I wish I had more top end but it is rare. The narrow wide chainring combined with the clutch on the derailleur really works - no dropped chains or slapping against the chainring.

Eric F 

I'm getting over things with my 34x36 now (including some 15-17% stuff yesterday), but find myself wanting a little lower gear from time to time on longer rides.

There are a multitude of different options I could go with. Some might end up working better for me. Some maybe not. At this point, parts are ordered and starting to get delivered for a 38 x 11-42 setup. I'm going to run with that until I see a reason to make a change.

SoSmellyAir

Woah! I did not know that one can adjust the clutch tension! Shimano's website just says on/off, but (after seeing your post) I looked up how to do that in the dealer manual. Learn something new every day.

SHIMANO GRX Rear Derailleur 11-speed (34T max low sprocket) | SHIMANO BIKE-EU
SHIMANO GRX Rear Derailleur 11-speed (42T max low sprocket) | SHIMANO BIKE-EU

Interestingly, the website mentions both a clutch and a stabilizer for RD-RX810, but only a stabilizer for RD-RX812.

jonathanf2

It's really easy to do and I actually think the stock tension is a bit too tight. I loosened mine just enough so it wouldn't affect shifting but still minimize chain whip.

Eric F 

Something ain’t right…

Ultegra 6800 levers
XT 11-42 cassette
GRX 812 rear derailleur

I cannot get this combination to index properly. Not even close.

The SRAM 11-36 cassette that came off did not have a spacer. Neither did the original 11-32 Ultegra cassette. Both worked great with Ultegra levers and Ultegra RD. XT cassette needed a spacer behind the cassette to tighten on the freehub.

It’s acting like the cog spacing of the XT cassette is narrower than the Ultegra and SRAM cassettes, and it doesn’t match up. Everything I read tells me the spacing should be the same.

What’s going wrong? What are my options?

Fentuz

11s road need ~36mm freehub. The old MTB 11s cassettes have the same thickness as a 9-10s cassette so it needs the spacer. Is your setup working with a 11-32 cassette? if so, that will clear the shifter/derailleur compatibility.

With the big cassette, when does it not index? is it all of them or the biggest?
Have you checked the derailleur hanger? is it straight?

Can you post pictures?

Eric F 

With the 11-42, when I adjust cable tension, etc. to work correctly starting from small-to-large it gets progressively worse as it gores across the cassette, to the point where it will skip over 2 cogs, and then have an extra shifter click left at the end. Same kind of thing going in the opposite direction.

I think this (the bold part) is the issue. I bought the cassette off eBay, and the lockring says M8000, but I have no guarantee that the lockring and cassette have always been together. Different cog spacing absolutely makes sense for the issues I'm having. I will reinstall the 11-36 to test this.


I'm going on vacation and taking this bike with me (I hope). It's looking a lot like I won't be able to run the configuration I was hoping. The 38T ring I ordered was wrong (GRX, not Ultegra), so at the moment, I only have a 34T ring up front. I'll make do with that and an 11-36 cassette, If I need to for now.

Grrr....

Fentuz

have you measured your spacer? It should be 1.8/2.0 mm thick from memory (i had to fit one of a wheelset I run with a 9s cassette for weight reason)

you could run a Sram PG1130 and get it overnight? 11-42 classic sram cassette compatible with shimano grx

Eric F 

It's not a spacer issue. The cassette sits easily within the range of the high and low limits of the derailleur, and there is plenty of clearance for the chain at the seatstay, when in the 11T cog.

I'm going to check things tonight with the SRAM 11-36 I have before I order anything else. This should confirm whether or not it's a cog spacing issue.

jonathanf2

Sounds like a bent derailleur hanger issue to me. Especially since you were coming from a non shadow Ultegra 6800 RD. A non-shadow RD is more prone to bending the RD hanger especially if the bike gets dropped on the drive side. My old 105 5800 RD setup had the same issue where it'd get progressively worst as you shifted to the low gears. I went to my LBS and had them straighten the hanger out for like $15-30 bucks.

Eric F 

Possibly. Everything looks pretty straight, but it's something I will check closer. This is an excuse for me to buy a derailleur alignment tool. Yay! New tools!!

I reinstalled the Ultegra RD and SRAM 11-36 cassette (the parts I had just taken off). I still had the same indexing issues that I had with the GRX and 11-42 setup. Super frustrating!! Trying to retrace my steps even more, I replaced the new derailleur cable with another one. That improved things. Apparently, the cable had gotten kinked in a couple of places during installation, and that may have been a big contributor to my issues. The shifting isn't perfect (a little noisy on the 2 biggest cogs), but it's rideable. For now, I'm going to set is aside until I can spend more time with it, and start from scratch again with the GRX and 11-42 setup. I'm going out of town for a week starting tomorrow, and have decided to take my road bike instead.

Doing some research on my issues, I found out why I needed a spacer for the XT 11-42 cassette, but not the Ultegra or SRAM cassettes. On Shimano 11s MTB cassettes, the inboard end of the cassette that fits over the freehub is inset from the face of the largest cog. Shimano 11s road cassettes are not inset. Cog spacing was not my issue.

jonathanf2

Even if it looks straight, it could be bent. Since you bought the bike used, it's still a good idea to have it aligned. This also why I'm a big fan of the current Shimano shadow RD design. I've dropped/crashed my gravel bike so many times and the hanger is still good. I'm even running a mismatched 10/11 speed drivetrain combo and it shifts like butter.