Shimano GRX 1x - 810 or 812 Rear Mech?
#1
Junior Member
Thread Starter
Shimano GRX 1x - 810 or 812 Rear Mech?
Hi - looking to build up my gravel bike with a 1x system. I have Shimano 105 11sp hydraulic shifters... looking for a rear mech. I wanted to clarify a few things with GRX 812 and GRX 810.
GRX 812 specs:
Any input would be greatly appreciated. My goal is to run a 38 or 40 1x up front with a 10-46 or 10-50 cassette in the rear with my Shimano 105 R7020 shifter(s).
Thank you!
GRX 812 specs:
- Top sprocket: Max. 11T/Min. 11T
- Low sprocket: Max. 42T/Min. 40T
- Total capacity: 31T
- Maximum front difference: 17T
- Top sprocket: Max. 11T/Min. 11T
- Low sprocket: Max. 34T/Min. 30T
- Total capacity: 40T
Any input would be greatly appreciated. My goal is to run a 38 or 40 1x up front with a 10-46 or 10-50 cassette in the rear with my Shimano 105 R7020 shifter(s).
Thank you!
#2
Senior Member
Join Date: Jan 2013
Location: South Jersey
Posts: 2,262
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 713 Post(s)
Liked 796 Times
in
473 Posts
The 810 has a Max large cog size of 34t, so you could go to a 36t without any problems, but a 10-50 cassette is out of the question. The total capacity of 40t means that it can take up the slack from a difference of 40 teeth, but the geometry of the derailleur will not allow the upper pulley to clear anywhere near a 50t cog.
If you want a 1x, use the GRX 812, but a 10-50 cassette would still be too big. If you want low gearing, go with the 2x and the 46/30 GRX crankset. 1x just doesn't make much sense for a gravel bike, unless you live in a relatively flat area.
If you want a 1x, use the GRX 812, but a 10-50 cassette would still be too big. If you want low gearing, go with the 2x and the 46/30 GRX crankset. 1x just doesn't make much sense for a gravel bike, unless you live in a relatively flat area.
#3
Senior Member
Join Date: Jun 2012
Location: Stillwater, OK
Posts: 7,827
Mentioned: 33 Post(s)
Tagged: 0 Thread(s)
Quoted: 1872 Post(s)
Liked 692 Times
in
468 Posts
Hi - looking to build up my gravel bike with a 1x system. I have Shimano 105 11sp hydraulic shifters... looking for a rear mech. I wanted to clarify a few things with GRX 812 and GRX 810.
GRX 812 specs:
Any input would be greatly appreciated. My goal is to run a 38 or 40 1x up front with a 10-46 or 10-50 cassette in the rear with my Shimano 105 R7020 shifter(s).
Thank you!
GRX 812 specs:
- Top sprocket: Max. 11T/Min. 11T
- Low sprocket: Max. 42T/Min. 40T
- Total capacity: 31T
- Maximum front difference: 17T
- Top sprocket: Max. 11T/Min. 11T
- Low sprocket: Max. 34T/Min. 30T
- Total capacity: 40T
Any input would be greatly appreciated. My goal is to run a 38 or 40 1x up front with a 10-46 or 10-50 cassette in the rear with my Shimano 105 R7020 shifter(s).
Thank you!
__________________
2014 Cannondale SuperSix EVO 2
2019 Salsa Warbird
2014 Cannondale SuperSix EVO 2
2019 Salsa Warbird
#4
Senior Member
Join Date: Mar 2006
Location: Chicago, IL, USA
Posts: 2,873
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 1455 Post(s)
Liked 1,477 Times
in
867 Posts
GRX 1x max cassette size is 11-42. Some internet forums indicate 11-46 can work, so this might be the biggest option for you.
You'll need a MTB rear derailleur to work on a 10-50, and there isn't one that would be compatible with 105 road shifters. If you want to dive into SRAM eTap AXS, you can run a "mullet build" with MTB rear mech, and road shifters.
2x is the obvious solution, but that's answering a question you didn't ask.
You'll need a MTB rear derailleur to work on a 10-50, and there isn't one that would be compatible with 105 road shifters. If you want to dive into SRAM eTap AXS, you can run a "mullet build" with MTB rear mech, and road shifters.
2x is the obvious solution, but that's answering a question you didn't ask.
Likes For msu2001la:
#5
Senior Member
Join Date: Oct 2006
Location: Orange County, CA
Posts: 4,770
Mentioned: 11 Post(s)
Tagged: 0 Thread(s)
Quoted: 630 Post(s)
Likes: 0
Liked 369 Times
in
206 Posts
Sram Type 3 road/gravel long cage rear deraillers will also fit 10-46T no problem. For 10-50+ you will need to hack a SRAM eagle mountain bike derailer.
Likes For Elvo:
#6
Junior Member
Thread Starter
Got it - appreciate the reply. Did you end up going with a GRX 812 rear mech?
#7
Senior Member
Join Date: Jun 2012
Location: Stillwater, OK
Posts: 7,827
Mentioned: 33 Post(s)
Tagged: 0 Thread(s)
Quoted: 1872 Post(s)
Liked 692 Times
in
468 Posts
__________________
2014 Cannondale SuperSix EVO 2
2019 Salsa Warbird
2014 Cannondale SuperSix EVO 2
2019 Salsa Warbird
Likes For shoota:
#8
Senior Member
Join Date: May 2009
Location: Brazil, Londrina PR
Posts: 273
Bikes: Kona Unit, Kona Kahuna, Kona Dew DL, Scott Big Jon, Trek Checkpoint ALR4, KHS Urban Soul, Haro Team Issue, GT Force Expert Carbon, Bernardi Quadra.
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 31 Post(s)
Liked 48 Times
in
25 Posts
The 812 is the 1x specific rear derailleur, Shimano claims a 42t maximum rear cog but I run an XT 11-46 on my bike with the 812 and have 0 problems. I have a second wheelset with an SLX 11-42 cassete and I swap back forth witthout any need to readjust anything. I even filmed the shifting with the 11-46 cassete the day I got the bike built.
If you need the 10t cog you may find a 10-46 cassete from brands like Sunrace and Zitto but you will have to upgrade your rear hub to an Xd Driver. And if you want to go all out, get the Di2 stuff and use a GRX Di2 shifter with an XT or XTR Di2 rear derailleur, the XT can handle an 11-50 just fine,I run an 11-50 with an XT M8000 derailleur on my XC bike.
If you need the 10t cog you may find a 10-46 cassete from brands like Sunrace and Zitto but you will have to upgrade your rear hub to an Xd Driver. And if you want to go all out, get the Di2 stuff and use a GRX Di2 shifter with an XT or XTR Di2 rear derailleur, the XT can handle an 11-50 just fine,I run an 11-50 with an XT M8000 derailleur on my XC bike.
Last edited by MAGAIVER; 12-21-20 at 06:53 AM.
Likes For MAGAIVER:
#9
Junior Member
Thread Starter
The 812 is the 1x specific rear derailleur, Shimano claims a 42t maximum rear cog but I run an XT 11-46 on my bike with the 812 and have 0 problems. I have a second wheelset with an SLX 11-42 cassete and I swap back forth witthout any need to readjust anything. I even filmed the shifting with the 11-46 cassete the day I got the bike built.
If you need the 10t cog you may find a 10-46 cassete from brands like Sunrace and Zitto but you will have to upgrade your rear hub to an Xd Driver. And if you want to go all out, get the Di2 stuff and use a GRX Di2 shifter with an XT or XTR Di2 rear derailleur, the XT can handle an 11-50 just fine,I run an 11-50 with an XT M8000 derailleur on my XC bike.
https://www.youtube.com/watch?v=71PgvwolgEE
If you need the 10t cog you may find a 10-46 cassete from brands like Sunrace and Zitto but you will have to upgrade your rear hub to an Xd Driver. And if you want to go all out, get the Di2 stuff and use a GRX Di2 shifter with an XT or XTR Di2 rear derailleur, the XT can handle an 11-50 just fine,I run an 11-50 with an XT M8000 derailleur on my XC bike.
https://www.youtube.com/watch?v=71PgvwolgEE
#10
Senior Member
Join Date: May 2009
Location: Brazil, Londrina PR
Posts: 273
Bikes: Kona Unit, Kona Kahuna, Kona Dew DL, Scott Big Jon, Trek Checkpoint ALR4, KHS Urban Soul, Haro Team Issue, GT Force Expert Carbon, Bernardi Quadra.
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 31 Post(s)
Liked 48 Times
in
25 Posts
I haven't been able to ride it as much as I'd like to but I had no issues with it so far, shifts perfect, the 812 looks a lot like an XT 11 speed RD and Shimano is usually very conservative on the derailleur capacity quotes. I am running a 40t ring on that bike.
#11
With a mighty wind
Join Date: May 2015
Posts: 2,576
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1084 Post(s)
Liked 854 Times
in
483 Posts
Are you loaded up on the bike?
Are you using it on very technical rocky and rooty steep climbing?
I ask this because those situations are where ultra low gearing really shines.
For gravel riding, in Colorado, with occasional mediocre mountain biking thrown in, you're about as low as you need.
40x42 is almost enough for anything a one day unloaded bike might see. If you go 38x42 or 42x46, you're not going to need more.
Down the hills, especially on washboards and switchbacks, I rarely find myself pedaling much past 20mph. If I find myself on pavement, sure I run out of high gears but it's fairly inconsequential with a good tuck.
I currently run 40x11-36 most times and occasionally switch to 11-42. On a 22 lb bike. That's where I base most of this on.
My new bike, a Swiss Cross, will be running 11-46 and a 44 for 90% of my rides. I'm giving myself the option to switch to a 38t chainring for oddball days.
I do think you're thinking in the right direction, gearing for all major groups is reflective of fast riders on fast courses and there's not a single complete group on the market that fits so many peoples needs. Ekar is the closest thing but $$$$$!
Are you using it on very technical rocky and rooty steep climbing?
I ask this because those situations are where ultra low gearing really shines.
For gravel riding, in Colorado, with occasional mediocre mountain biking thrown in, you're about as low as you need.
40x42 is almost enough for anything a one day unloaded bike might see. If you go 38x42 or 42x46, you're not going to need more.
Down the hills, especially on washboards and switchbacks, I rarely find myself pedaling much past 20mph. If I find myself on pavement, sure I run out of high gears but it's fairly inconsequential with a good tuck.
I currently run 40x11-36 most times and occasionally switch to 11-42. On a 22 lb bike. That's where I base most of this on.
My new bike, a Swiss Cross, will be running 11-46 and a 44 for 90% of my rides. I'm giving myself the option to switch to a 38t chainring for oddball days.
I do think you're thinking in the right direction, gearing for all major groups is reflective of fast riders on fast courses and there's not a single complete group on the market that fits so many peoples needs. Ekar is the closest thing but $$$$$!
#12
Senior Member
Join Date: Jan 2020
Location: San Jose
Posts: 1,025
Bikes: Blur / Ibis Hakka MX / team machince alr2 / topstone 1
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 426 Post(s)
Liked 274 Times
in
201 Posts
if you convert a 2x bike that came with grx 810 to 1x can you use a road link so the 11-46T would work?
or do you need the grx 812 to make the 11-46T work?
I know grx 812 works with the 11-46T because it came that way from the factory on my grx equiped Ibis MX.
https://www.ibiscycles.com/bikes/hakka-mx
or do you need the grx 812 to make the 11-46T work?
I know grx 812 works with the 11-46T because it came that way from the factory on my grx equiped Ibis MX.
https://www.ibiscycles.com/bikes/hakka-mx
#13
Senior Member
Somewhat, although it's unlikely to shift as well as the 812 in that case. I actually know a guy who was using an 11-46 cassette with the 810 on a 2x drivetrain, but it was really straining the boundaries of good behavior.
Likes For HTupolev:
#14
Full Member
Join Date: Apr 2018
Location: NYC
Posts: 383
Bikes: '72 Raleigh Super Course; '90 Cannondale ST1000; '98/99 Cannondale T700; 2002 Cannondale CAAD5 R700; 2022 Cannondale Topstone 2L
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 166 Post(s)
Liked 348 Times
in
156 Posts
Old thread but I watched this video earlier this week and it seems at least somewhat applicable to the conversion.
Likes For Rooney:
#15
Newbie
Join Date: Jun 2023
Posts: 1
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Hi, I'm hoping someone can advise here.
I have a 2x11 set up on a gravel bike with Shimano GRX810 rear derailleur. It's damaged but a friend has an 812 from his Cannondale Topstone (written off) he said I can have.
I'm a noob when it comes to the technical side of things. Can I just straight swap this on to mine. My cassette is 11-34 and the front is 46/30
I've read the stuff at the start of this thread but don't really understand.
Many thanks.
I have a 2x11 set up on a gravel bike with Shimano GRX810 rear derailleur. It's damaged but a friend has an 812 from his Cannondale Topstone (written off) he said I can have.
I'm a noob when it comes to the technical side of things. Can I just straight swap this on to mine. My cassette is 11-34 and the front is 46/30
I've read the stuff at the start of this thread but don't really understand.
Many thanks.
#16
Senior Member
Join Date: Jan 2020
Location: San Jose
Posts: 1,025
Bikes: Blur / Ibis Hakka MX / team machince alr2 / topstone 1
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 426 Post(s)
Liked 274 Times
in
201 Posts
Hi, I'm hoping someone can advise here.
I have a 2x11 set up on a gravel bike with Shimano GRX810 rear derailleur. It's damaged but a friend has an 812 from his Cannondale Topstone (written off) he said I can have.
I'm a noob when it comes to the technical side of things. Can I just straight swap this on to mine. My cassette is 11-34 and the front is 46/30
I've read the stuff at the start of this thread but don't really understand.
Many thanks.
I have a 2x11 set up on a gravel bike with Shimano GRX810 rear derailleur. It's damaged but a friend has an 812 from his Cannondale Topstone (written off) he said I can have.
I'm a noob when it comes to the technical side of things. Can I just straight swap this on to mine. My cassette is 11-34 and the front is 46/30
I've read the stuff at the start of this thread but don't really understand.
Many thanks.
Shimano recommendation.
https://bike.shimano.com/en-US/produ.../RD-RX812.html
Total capacity: 31T
You have 39 spread.
46-30 = 16 in the front
11-34T = 23 in the back
16 + 23 = 39
Since it's free just try it. If it has too much slack in the small and small gear you can then decide on buy a grx 810 rear mech or buying a smaller rear cassette.