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GRX Di2

Old 09-02-20, 03:43 AM
  #26  
srode1
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Originally Posted by pduncanj View Post
Hi and great to see all this helpful info. I too am setting up (or trying to) an RD RX817 in a 2 x configuration, but with an ultegra FD R8050 front derailleur. I have encountered some issues not mentioned in this string.

- Alignment: I don’t know what frame specs the 817 is intended for, but the intended limits on movement (physical, not electronic) are way inboard of a standard setup. I have a 142mm OLD back end, which should be standard for this mech - but low screw has to be way in, stopper on body doesn’t even touch high screw. I had to put a washer between derailleur link and hanger, just to get guide wheel outboard far enough to run on smallest sprocket. Sounds mega-crude but given that Di2 limits are essentially set thru shift adjustment (I know the screws are there but I can see no reason why it wouldn’t function without a hard high limit in place) this could potentially fly I guess. Not very elegant tho, to say the least. And perhaps risks of chain jam, without hard stop. Any explanation of why this derailleur would be designed this way? I am using an SLX 11-40 cassette with a 1.85mm spacer. Removing the spacer would help but would mess up chain line and perhaps bring jockey cage uncomfortably close to spokes.

- This is what happens when you shift from big ring to small: click 1: jumps 2 at rear; click 2: jumps another 2; click 3: changes ring. This leaves you on 5th smallest sprocket. It will then allow a shift to 4th smallest = smallest useable sprocket when on small ring. I guess this is Shimano’s way of being flexible enough to allow use of their ‘1 x’ mech in a 2 x setup?? Or is it due to the GRX-Ultegra derailleur mix??

I connected to E-Tube app (on laptop not phone) and tried to over-ride the small-small lockout in the usual way (long story if you don't know how). This crashed the app and initially bricked the system - nice. Luckily when I rebooted the app and reconnected the system it came back up. At some point I got a pop-up message about non-compatible derailleurs. So not possible to over-ride small-small lockout.

Funnily enough tho, losing all those gears doesn’t matter that much as they are duplicated on the big ring (ran the numbers).

One reason why Shimano may lock out the smaller sprockets (if they thought about it this hard): the standard cage on the RRX817 is pretty short, wouldn't allow sufficient wrap for a wide range 2 x setup.

Incidentally and for info - and I can't see how this would cause any of the issues I've mentioned - I modified the RX817 by fitting the longer cage from an RD M8000 SGS (mechanical), in order to get more chain wrap. The cages will swap OK, with some minor issues which I can explain if anyone's interested. The cage sits in exactly the same position as the original cage so this can't be causing the alignment issues mentioned above.

I was a bike mechanic in a former life so any basic or obvious solutions are unlikely to work. Thanks for reading / responding ...
The DR isn't designed for anything special on the rear end, it should fit on any frameset that an ultegra DR would work on. The 815 is the same and it will fit on anything. The jumping 2 and then another 2 before the 3rd click doing the front shift may well be a result of the "incompatibility" problem your pop up message indicated. I use a front 8050 and a rear GRX 815 with no issues at all.

Personally, I would start from scratch again and make sure I didn't miss something in the set up starting with the bolting on of the Rear DR to the frame and in the Di2 set up. Ditch all the spacers you have and use the limit screws following the Shimano instructions for set up. The only thing that could have the alignment problem if installed correctly is a bent hanger. Make sure the stop block on the link arm is on the right side of the spot the old "B" screw push point on your DR hanger and that it's right up against it. That won't rotate in place after you tighten down the DR, you need to move it to be in contact before you torque the fastener, but that's the same as the 8050 also.

Last edited by srode1; 09-02-20 at 03:50 AM.
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Old 09-02-20, 04:14 AM
  #27  
pduncanj
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Originally Posted by srode1 View Post
The DR isn't designed for anything special on the rear end, it should fit on any frameset that an ultegra DR would work on. The 815 is the same and it will fit on anything. The jumping 2 and then another 2 before the 3rd click doing the front shift may well be a result of the "incompatibility" problem your pop up message indicated. I use a front 8050 and a rear GRX 815 with no issues at all.

Personally, I would start from scratch again and make sure I didn't miss something in the set up starting with the bolting on of the Rear DR to the frame and in the Di2 set up. Ditch all the spacers you have and use the limit screws following the Shimano instructions for set up. The only thing that could have the alignment problem if installed correctly is a bent hanger. Make sure the stop block on the link arm is on the right side of the spot the old "B" screw push point on your DR hanger and that it's right up against it. That won't rotate in place after you tighten down the DR, you need to move it to be in contact before you torque the fastener, but that's the same as the 8050 also.
Thank you for the quick reply.

"I use a front 8050 and a rear GRX 815 with no issues at all": 815 has a longer cage and is designed for 2 x so this probably explains why you don't get the same problem. I am using 817 as the cage is (somewhat) compatible to swap with the M8000 SGS.

I should've mentioned: this is not a new build, just swapping out rear mech on an existing Felt VR2 2018. RD R8050 was fitted as stock and with no issues. So unfortunately nothing you suggest in fitment applies (and I am familiar with fitting these / no mistakes).
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Old 09-02-20, 04:22 AM
  #28  
srode1
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Originally Posted by pduncanj View Post
Thank you for the quick reply.

"I use a front 8050 and a rear GRX 815 with no issues at all": 815 has a longer cage and is designed for 2 x so this probably explains why you don't get the same problem. I am using 817 as the cage is (somewhat) compatible to swap with the M8000 SGS.

I should've mentioned: this is not a new build, just swapping out rear mech on an existing Felt VR2 2018. RD R8050 was fitted as stock and with no issues. So unfortunately nothing you suggest in fitment applies (and I am familiar with fitting these / no mistakes).
Curious, what is it you are trying to achieve with the 817 instead of using an 815? Maybe you had an 817 readily available?

The cage difference between 815 and 817 obviously has nothing to do with the limit problems you are seeing or the odd triple click needed to move the front to the small ring - the Di2 system doesn't know what cage you have only the DR body.

Please post what you find if you resolve it - I'm curious now.
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Old 09-02-20, 04:38 AM
  #29  
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Originally Posted by srode1 View Post
Curious, what is it you are trying to achieve with the 817 instead of using an 815? Maybe you had an 817 readily available?

The cage difference between 815 and 817 obviously has nothing to do with the limit problems you are seeing or the odd triple click needed to move the front to the small ring - the Di2 system doesn't know what cage you have only the DR body.

Please post what you find if you resolve it - I'm curious now.
I am using 817 as the cage is (somewhat) compatible to swap with the M8000 SGS. I have fitted a M8000 SGS jockey cage to the 817, as that very long cage has a massive 47T wrap capacity, compared with 38T for the 815. 815 is a completely different design to 817 and the SGS cage would not fit.
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Old 09-09-20, 06:11 AM
  #30  
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Originally Posted by srode1 View Post
Nice build. I am curious why you chose the 817 RD instead of the 815 when there is less take up on the 817 and the 815 reportedly works with an 11/42 cassette.
I thought the 817 would be a better fit for the system with the 42t rear cassette. Turns out the 817 has an SS length cage and didn't have quite as much chain wrap as I had expected. Overall it seems to work well as is, but maybe not an optimal set up.
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Old 09-09-20, 06:17 AM
  #31  
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Originally Posted by pduncanj View Post
I am using 817 as the cage is (somewhat) compatible to swap with the M8000 SGS. I have fitted a M8000 SGS jockey cage to the 817, as that very long cage has a massive 47T wrap capacity, compared with 38T for the 815. 815 is a completely different design to 817 and the SGS cage would not fit.
Interesting to see that the M8000 cage will swap over. I may look into that as that would help with the big/big combination.

My system reacts the same way if you are on the 11t cog and want to shift to the small ring. It will shift the rear to the 4th smallest cog before shifting the front. Like you said, not a big deal. If it didn't do this the chain would be flopping around.
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Old 09-24-20, 02:43 PM
  #32  
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I'm a long time mt biker and devotee of SRAM 1x 12 mechanical. When the time came to get a gravel bike the dealer sold me on GRX Di2 2x. So glad he did, for me its been the optimal drivetrain for this sort of bike. I think I'd get Shimano Di2 on any 2x/drop bar bike. the 48/31 and 11x34 is a good range of gearing for the riding I do.
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Old 09-27-20, 03:02 AM
  #33  
Badger6
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Nice post, like the details on the setup. I definitely have questions on the 817 choice, but nothing worth asking that isn't being explained by the other posts, and doing some inference...but this part I've quoted...

Originally Posted by Bryan C. View Post
I absolutely HATE the Sram Force 1 hydraulic brakes. Even after the upgrade to 4 piston Hope RX4 calipers the brakes still didn't improve much. They're probably OK if you weigh under 170 lbs but for me at 210+ pounds they left me with hand cramps and taking descents at a much higher speed than I would prefer.
I just did a total brake upgrade on my 2015 Diverge (nothing original on that bike anymore, 3rd frame, and 5th build...long story, not worth telling here). I love the frame geometry and how it rides. But, the calipers were the old 785 non-series calipers, the "original" road caliper, but definitely several generations old, and proven to be somewhat unreliable and not very durable over time. Because the frame is post mount, and with the shift to flat mount for road/gravel in the industry, the brake options were severely limited...as in, not available unless I want to do 785s again. The RX4 post mount are completely unavailable, sold out, everywhere, and it appears Hope discontinued them, because "flat mounts" I suspect.

So what did I do? Expanded my search to MTB brake calipers. Plenty of opinions, apparently not based on actual testing that the MTB calipers wouldn't work well (or at all) with a road/gravel lever due to the differences in how much fluid each pushed. Further, Shimano doesn't explicitly say they won't work, but there is NO reference to pairing them with a drop bar lever. I took a chance, well educated mind you, that because they use BH90 hosing—in terms of part interface—they would theoretically work. I'll make a separate post detailing what I did, but I got them working nicely. My point in this: as you've discovered with your build, with a bit of mechanical know how, and general understanding of how the parts of a modern drivetrain and braking system fit together, and mount to the bike, getting the setup we really want is possible with some creativity and planning.

Nice build, and well done!
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Old 09-28-20, 02:14 PM
  #34  
jan nikolajsen 
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Same here: GRX Di2 levers on a post mount drop bar gravel frame. Found a set of Deore brakes with leaking levers from an old townie. Calipers and hoses were good so I hooked them up to the GRX levers. This is eight months and lots of miles ago, and no regrets. Much easier than the earlier project of converting said gravel frame to Di2!

Originally Posted by Badger6 View Post

So what did I do? Expanded my search to MTB brake calipers. Plenty of opinions, apparently not based on actual testing that the MTB calipers wouldn't work well (or at all) with a road/gravel lever due to the differences in how much fluid each pushed. Further, Shimano doesn't explicitly say they won't work, but there is NO reference to pairing them with a drop bar lever. I took a chance, well educated mind you, that because they use BH90 hosing—in terms of part interface—they would theoretically work. I'll make a separate post detailing what I did, but I got them working nicely.
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Old 03-04-21, 12:03 PM
  #35  
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How about another update nobody asked for?

I located a GRX 815 derailer and swapped that onto my Diverge.

Other than needing a slightly longer chain the system is working well with the 11-42 cassette. The GS length cage was an improvement over the short SS cage on the 817.

Last edited by Bryan C.; 03-04-21 at 12:06 PM.
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Old 03-04-21, 12:04 PM
  #36  
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And the real reason for the thread bump....

As of today, GRX Di2 2x drivetrain is in stock at Merlin.

https://www.merlincycles.com/en-us/s...eid=4e44856289
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Old 03-05-21, 02:00 AM
  #37  
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Nice update. Have you looked at synchro since installing the RD-815?
I'm not sure whether or not that's useful on a GRX build, but I thought I'd ask ;-)
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Old 03-06-21, 01:54 PM
  #38  
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Originally Posted by TerryDi2C View Post
Nice update. Have you looked at synchro since installing the RD-815?
I'm not sure whether or not that's useful on a GRX build, but I thought I'd ask ;-)
Funny you should ask that. Once the 815 was installed the semi-synchronized shift became enabled without my knowledge. The presence of the former 817 RD shut off all those features even though they were apparently turned on with the app. I noticed it acted funny after a front shift. Turns out it was me fighting with a compensating rear shift. Once I got my app up and running on my new phone I was able to shut that crap off.

I did notice the new Etube app is much easier to use though. That was a nice surprise.
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