Is the Shimano Di2 GRX RD-RX817 limited to 1x11?

[DRZRM]

Most descriptions of this RD hype its ability to take a 11-42 cassette on a road/gravel frame and several sellers describe it as 1x11 specific. If I wanted to run two rings up front, besides the fact that I would have to use a Di2 road FD are there limitations? Is that what it means when Shimano says total capacity is 31T?

If I do have to use a RD with a top cassette size of 34T, is there any significant difference between the GRX line RD-RX815 and the medium cage Ultegra RD-RX805-GS.

They both have clutch, they take the same size cassette, they both work with the same shifters, right? Any reason to exclude one, or just wait for the best sale?

[John H.]

I have been running the 817 GRX rear derailleur with a double set-up since summer.
It works great with 34/50 up front and 11-40 or 11-42 in back.

[DRZRM]

And if I don't want to use the GRX wider cranks, I can use a standard Ultegra FD-R8050 front paired with the RD-RX817? It all plugs and plays right?

Last question, is it just a wider BB spindle on the GRX crankset that sets it apart? Or are the rings actually spaced differently? I have an Easton ec90 crank with 32/47 rings. I'd be fine with an 11-34 cassette and I could use standard Ultegra stuff, but I already have a gravel bike with similar gearing. I was thinking I'd make my next one a bit more trail worthy with bigger tires and lower gearing. Don't suppose they have a longer spindle with a spacer for the cup to make their crank GRX compatible?

[RacerJRP]

What you'll need to watch out for running a regular Ultegra FD is potential rubbing on the FD cage with the chain at more extreme angles or running very small inner ring. The GRX cage is deeper, more like a MTB cage.

So....it depends on the total gearing setup you are looking to run.

[eddief]

https://gravelcyclist.com/videos/shi...-xtr-cassette/

[John H.]

Depends on the crank you are running. I am using a Dura-Ace DI2- no rub at all.
Crank is a 34/50 with Dura-Ace 9100 rings.

QUOTE=RacerJRP;2637645]What you'll need to watch out for running a regular Ultegra FD is potential rubbing on the FD cage with the chain at more extreme angles or running very small inner ring. The GRX cage is deeper, more like a MTB cage.

So....it depends on the total gearing setup you are looking to run.[/QUOTE]

[bikinchris]

Originally Posted by DRZRM

And if I don't want to use the GRX wider cranks, I can use a standard Ultegra FD-R8050 front paired with the RD-RX817? It all plugs and plays right?

Last question, is it just a wider BB spindle on the GRX crankset that sets it apart? Or are the rings actually spaced differently? I have an Easton ec90 crank with 32/47 rings. I'd be fine with an 11-34 cassette and I could use standard Ultegra stuff, but I already have a gravel bike with similar gearing. I was thinking I'd make my next one a bit more trail worthy with bigger tires and lower gearing. Don't suppose they have a longer spindle with a spacer for the cup to make their crank GRX compatible?

In the training video for GRX, it just tells us that they moved the chainrings out to clear the wider tires. I suspect the crankarm itself is different, not the spindle.

[RacerJRP]

Exactly. With your more standard 34t inner ring shouldn't be issues. If he was going to run a 31t or something smaller like that he would likely drag the chain on the bottom of the FD cage. But you never know!

Originally Posted by John H.

Depends on the crank you are running. I am using a Dura-Ace DI2- no rub at all.
Crank is a 34/50 with Dura-Ace 9100 rings.

QUOTE=RacerJRP;2637645]What you'll need to watch out for running a regular Ultegra FD is potential rubbing on the FD cage with the chain at more extreme angles or running very small inner ring. The GRX cage is deeper, more like a MTB cage.

So....it depends on the total gearing setup you are looking to run.

[/QUOTE]

[John H.]

He would also likely be using GRX crank for 31-48 so he would be best served by getting the matching FD.

Originally Posted by RacerJRP

Exactly. With your more standard 34t inner ring shouldn't be issues. If he was going to run a 31t or something smaller like that he would likely drag the chain on the bottom of the FD cage. But you never know!

[/QUOTE]

[N.eilo]

Would there be an issue running the bigger 817 mech on a 34 max cassette?

[Jere]

Originally Posted by DRZRM

Most descriptions of this RD hype its ability to take a 11-42 cassette on a road/gravel frame and several sellers describe it as 1x11 specific. If I wanted to run two rings up front, besides the fact that I would have to use a Di2 road FD are there limitations? Is that what it means when Shimano says total capacity is 31T?

If I do have to use a RD with a top cassette size of 34T, is there any significant difference between the GRX line RD-RX815 and the medium cage Ultegra RD-RX805-GS.

They both have clutch, they take the same size cassette, they both work with the same shifters, right? Any reason to exclude one, or just wait for the best sale?

The 817 will not play well with Road 52/36
And you lose some Di2 functions
How do I know

https://forums.thepaceline.net/showthread.php?t=296009

[Dave]

I use grx cranks. The chainline is +2.5mm, compared to road bike, but any 105, ultegra or DA BB works, I use wheels manufacturing thread together with angular contact bearings. I have road bikes and correct the chain line with 2mm spacing washers that move the rings inward. The rest is SRAM AXS.

[N.eilo]

Originally Posted by Jere

The 817 will not play well with Road 52/36
And you lose some Di2 functions
How do I know

https://forums.thepaceline.net/showthread.php?t=296009

Is the 815 more Ultegra friendly? I am trying to avoid using a Wolftooth road link with my Ultegra DI2 road system as it makes shift hit and miss. I have along cage from a cable Ultegra mech but this does not get around the B gap between the cassette and top pulley wheel which as mentioned is not totally fixed by the Wolftooth hanger extender.

[Jere]

Originally Posted by N.eilo

Is the 815 more Ultegra friendly? I am trying to avoid using a Wolftooth road link with my Ultegra DI2 road system as it makes shift hit and miss. I have along cage from a cable Ultegra mech but this does not get around the B gap between the cassette and top pulley wheel which as mentioned is not totally fixed by the Wolftooth hanger extender.

Hi
On my gravel bikes I run 11/40 cassettes on 4 wheelsets
Front 34/50 road cranks I gave up on 36/52 cranks off road I’m too old.
Using RX 815 and GS 805 rear.
Chain length is critical , too long and taking the slack up with the B screw
It will shift badly 11/12/14
And remember always check your rear derailer hanger even if it’s a new bike.

[N.eilo]

Originally Posted by Jere

Hi
On my gravel bikes I run 11/40 cassettes on 4 wheelsets
Front 34/50 road cranks I gave up on 36/52 cranks off road I’m too old.
Using RX 815 and GS 805 rear.
Chain length is critical , too long and taking the slack up with the B screw
It will shift badly 11/12/14
And remember always check your rear derailer hanger even if it’s a new bike.

Thanks for the advice, I'm running this on a road bike for a trip up to Northern Thailand where they have long and sometimes very steep climbs. I Canyon Grizl running GRX 810 2 x for off road duties