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GRX Di2

Old 05-22-20, 09:25 AM
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Bryan C. 
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GRX Di2

Recently I decided to upgrade my 2019 Diverge from a Sram Force 1x to a Shimano GRX Di2 2x drivetrain. The bike is too new for me to justify selling it and buying a new bike already equipped with electronic shifting. The overall cost would be similar, or even more, considering how much money I would lose selling the bike itself. It made sense for me to keep it and upgrade what I didn't like.

I was torn between a 1x12 Sram Force/Eagle set up and the GRX 2x. Most of my local LBS's have the Sram Force/Red/Eagle set ups on their high end bikes and were not easily available for me to test ride. My opinions of Sram are based only on what I was using, Sram Force 1.

Ultimately there were a few things that made the decision easy for me:

1) $700 for a Sram Eagle AXS rear derailleur to me is ridiculous. One good wipe out and you are out some serious cash for repairs. Sure, I don't think the average gravel rider is pushing the limits of their bike but my own recent experiences of wipe outs has shown that it can and will happen. Nobody plans to wipe out, but it sure does happen quickly when you run out of talent.
2) 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. Add to that me constantly comparing them to my road bike's Shimano DA brakes there really was no reason to continue on with them on my bike.
3) The lack of a bonafide Sram XC/gravel friendly 12 speed cassette. The recent release of the wide range gravel 2x AXS set up from Sram could have been a game changer had they made something similar to the Shimano 10-45 12 speed cassette. I'm not sure Sram is really interested in designing any drivetrain components for anyone other than strong riders. I guess that's their business model, and they are free to do as they want. For aftermarket cassette support all I could find was a 9-46 12 speed cassette from Rotor that would work ok but availability was very limited when I looked into it and the price was expensive.
4) Sram and their MAP pricing forces retailers to sell at full price. Not only that, most places do not discount Sram products or offer sales or incentives of any kind. The best deal I could find was clicking through rebate sites for whatever percentage rebate was offered. 10% or less is hardly anything to get excited about but it does add up if Sram is your go-to components.

Ok, enough with the Sram bashing. No need to pile on.

I chose the GRX Di2 based exclusively on the idea that the brakes would be a major improvement. And with transitioning to a 2x system I felt Shimano was the right choice for that. My build consisted of the following:
815 front and rear shifters, calipers, and L03a pads(more on that later)
815 front derailuer
817 rear derailuer
Bar end junction port with internal handlebar cable routing
Wireless/Bluetooth module
Sram 12 spd eagle chain
Sram 10-42 cassette
Praxis 48/32 double chainset

All of the major GRX components were purchased with a 20% off discount code and with an additional 12% off through a rebate site. Total savings in the neighborhood of $600 off of retail.

I chose to re-use the factory equipped Praxis Zyante carbon cranks. I simply changed the 1x chainring out for a 2x LT2 Praxis spider and chainring set. My preferred setup would be a 46/30 chainset with an 11-40 cassette but my Diverge can barely handle the 32t small chainring due to frame clearance issues with the chainring bolts. Ross over at Praxis helped me figure out how to work around this problem with using some shaved down chainring bolts. I was able to make it all work thanks to his help.

According to the bike gear calculator it shows this system has a 630% range. The 32/42 climbing ratio is pretty nice. The Sram cassette is fairly well spaced except for one combination that I seem to fall into regularly. I may try the Shimano 11-42 cassette as the jumps are small, 2 teeth, until you're near the mid-point of the cassette. Still working on that but for now the Sram cassette is staying in place.

The 817 RD does limit one feature of Di2, synchronized shifting. Without the matching front/rear 815 derailleurs, the system will not allow you to program the sync shifts. Not sure if anyone has found a work around for this yet but for now I can just shift the front as needed. Not a deal breaker for me but it may pose issues for those that use Di2 on multiple bikes and like that feature. The auto trim feature still works just fine so no worries about chain rubbing on the front derailleur cage.

Now the brakes. Shimano updated their L02a resin pads to a different compound. The new L03a pads came installed in the GRX calipers. This is probably my favorite part of the upgrade. I can't say enough about how much of an improvement these brakes are. Better stopping power, better modulation, and better power than the Sram brakes they replaced. Light riders may say they are too grabby, but if you are a fat ass like me then they will be perfect.

Overall the upgrade has been a complete success, and for me worth every penny.
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Old 05-22-20, 09:31 AM
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A couple pics:

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Old 05-22-20, 10:01 AM
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Re: Your inability to use the Sync mode in Di2. Perhaps you have Di2 on another bike and like the mode...If not, then you might not be missing much, depending on your preferences. I find that Sync works poorly for me: the FD shifts first, then the RD shifts with a slight lag, and this means that my cadence changes abruptly twice -- even though the mode is supposed to make those transitions between chainrings smoother. (To be fair, it is a little better when going from the small ring to the big one than vice-versa.)

Re: Shimano disc brakes. Yeah, they are fantastic. Mine are Ultegra, but the calipers are probably the same as GRX...But apparently the GRX levers offer even better modulation.
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Old 05-22-20, 11:44 AM
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If etap is truly wireless, and I was upgrading just the groupp I would lean towards that system because it would be much easier to transfer to a future bike. I don't have any experience with them to understand the +/- of shimano vs. sram electronic shifting though other than that.
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Old 05-22-20, 11:54 AM
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Not of much use to the OP now, but re: lack of good cassettes for AXS setups: I use the e*thirteen 9-46 12 speed cassette with my AXS mullet build (and 40t chainring). Plenty of range, I spin out on descents but otherwise am able to hit 25+ mph in flats while climbing steep walls, with somewhat noticeable gear gaps.
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Old 05-22-20, 12:07 PM
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Originally Posted by ArchEtech View Post
If etap is truly wireless, and I was upgrading just the groupp I would lean towards that system because it would be much easier to transfer to a future bike. I don't have any experience with them to understand the +/- of shimano vs. sram electronic shifting though other than that.
The wired vs. wireless aspects have their pros and cons. For Di2 I didn't consider it any more or less difficult than running derailleur cable. For most people the brake hoses need to be run inside the frame so you are there anyway with the tools needed to do the job in hand.

When comparing prices you do need to consider the extra cost of cables and junction ports with Di2. Including a battery, charger, ports, and cables, all that cost me close to $500.

Sram batteries and chargers aren't cheap either and need to be removed for charging. All the wireless communication hardware is built into the components which adds to their cost.

In my opinion neither one has the advantage.
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Old 05-22-20, 12:15 PM
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Originally Posted by blazin View Post
Not of much use to the OP now, but re: lack of good cassettes for AXS setups: I use the e*thirteen 9-46 12 speed cassette with my AXS mullet build (and 40t chainring). Plenty of range, I spin out on descents but otherwise am able to hit 25+ mph in flats while climbing steep walls, with somewhat noticeable gear gaps.
I figured there were more cassettes out there to choose from but stopped looking when I made my decision to go Di2. I tried the 9-46 11 speed cassette on it when I was trying to find something cassette wise that worked better. I liked the range and as you say the climbing was good, however I spun out quite often.

I realized what I wanted was smaller gaps on my cassette rather than wider range overall. So 2x I went.
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Old 05-22-20, 07:45 PM
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Originally Posted by ArchEtech View Post
If etap is truly wireless, and I was upgrading just the groupp I would lean towards that system because it would be much easier to transfer to a future bike. I don't have any experience with them to understand the +/- of shimano vs. sram electronic shifting though other than that.
etap is truly wireless, which is nice. Di2’s advantage is that you only have to worry about one battery - and it lasts a long time on a charge.
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Old 05-23-20, 06:42 PM
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Originally Posted by Koyote View Post
etap is truly wireless, which is nice. Di2’s advantage is that you only have to worry about one battery - and it lasts a long time on a charge.
True. Though I discovered one downside. I once had the Di2 battery in my seat post shaken loose during a long ride over some particularly rough gravel. Without tools, I was unable to fish the wire out from the seat tube to reconnect the battery and so had to single speed home. I suppose an eTap battery could get rattled loose too, but I carry a spare and can easily replace it.
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Old 05-23-20, 06:45 PM
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Originally Posted by blazin View Post
True. Though I discovered one downside. I once had the Di2 battery in my seat post shaken loose during a long ride over some particularly rough gravel. Without tools, I was unable to fish the wire out from the seat tube to reconnect the battery and so had to single speed home. I suppose an eTap battery could get rattled loose too, but I carry a spare and can easily replace it.
Yikes. I hope that never happens to me. I like having multiple gears.
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Old 05-23-20, 06:51 PM
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Originally Posted by blazin View Post
True. Though I discovered one downside. I once had the Di2 battery in my seat post shaken loose during a long ride over some particularly rough gravel. Without tools, I was unable to fish the wire out from the seat tube to reconnect the battery and so had to single speed home. I suppose an eTap battery could get rattled loose too, but I carry a spare and can easily replace it.
insert the battery with the connector facing downwards, so even if the battery got loose it would still stay connected inside the seattube
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Old 05-23-20, 07:09 PM
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Originally Posted by Chi_Z View Post
insert the battery with the connector facing downwards, so even if the battery got loose it would still stay connected inside the seattube
The battery stayed in the seat post. So perhaps I did too good a job padding it and lodging it in there? Also, I was running the seat post at minimum insertion length, so the battery was relatively high up in the seat tube, potentially stretching the wire, but at the very bottom of the post, thus subject to vibration/movement. I doubt this is a very likely occurrence, but an interesting mode of failure nonetheless.
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Old 05-24-20, 12:40 PM
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Originally Posted by Chi_Z View Post
insert the battery with the connector facing downwards, so even if the battery got loose it would still stay connected inside the seattube
If using a rubber shim (Ritchey, Shimano) for the battery, it can only install into the seatpost with connector down, as per the instructions for the shim.
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Old 05-24-20, 04:55 PM
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No one has said it, so I'll say it: gorgeous bike and really nice build. The GRX Di2 levers are imo the best looking levers for drop bars. If they weren't so utterly out of my price range, I would run that setup in a second. When I first saw them on a bike in a magazine I thought they were some prototype Campagnolo levers since the silhouette reminds me of the 9/10 speed ergos back in the day. But they're like a digital version. So sick.
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Old 05-25-20, 05:24 AM
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Gorgeous bike indeed!

I have to admit I was surprised to see the RD-RX817 and a front derailleur - Shimano say the RD-RX817 can not be used with a front derailleur ;-)



[edit] so I had a quick look on some Shimano pages and found this:

The RD-RX817 is a clean-slate 1x-only rear derailleur. Its total chain capacity is less than the RD-M8050-GS because the XT derailleur was designed to work on either a 1x or 2x mountain drivetrain.
The specification page on si.shimano.com says this without saying it explicitly. The 31t total capacity is just enough to handle the 11-42.
Attempting to run a 2x11 setup with a 40 or 42 tooth large cog will give reduced shifting quality and may result in damage or injury.
Still, it clearly works for you, so enjoy ;-)

Last edited by TerryDi2C; 05-25-20 at 05:59 AM.
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Old 05-25-20, 06:30 AM
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Originally Posted by celesteguy View Post
No one has said it, so I'll say it: gorgeous bike and really nice build. The GRX Di2 levers are imo the best looking levers for drop bars. If they weren't so utterly out of my price range, I would run that setup in a second. When I first saw them on a bike in a magazine I thought they were some prototype Campagnolo levers since the silhouette reminds me of the 9/10 speed ergos back in the day. But they're like a digital version. So sick.
Thanks for the compliment. The GRX hoods looked weird every time I saw pictures of them. On the bike they look totally different and like you said they look great. Much better looking than my mechanical DA hoods on my road bike.

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Old 05-25-20, 06:59 AM
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Originally Posted by TerryDi2C View Post
Gorgeous bike indeed!

I have to admit I was surprised to see the RD-RX817 and a front derailleur - Shimano say the RD-RX817 can not be used with a front derailleur ;-)



[edit] so I had a quick look on some Shimano pages and found this:





Still, it clearly works for you, so enjoy ;-)


Thanks for the info. I was a bit concerned about whether it would work too. I did a little bit of searching and couldn't easily find anyone who had tried it. I took a chance and it seemed to work out just fine, well minus the synchronized shifting. Took some time to work through chain length and the b-screw set up but I'm very happy with the result.

RE: GRX 817 vs. XT 8050. In my opinion these are the same derailleurs just with different markings. I don't own an 8050 but I do own an XT M8000 GS cage derailleur on my MTB. When comparing the GRX and the XT side by side they are literally identical in size and shape. Might be an optical illusion but it seems like the GRX 817 can handle more than the 42t max it states. I'm set on the 42t cassette anyway so no need for me to push any bigger. I imagine someone could run an e-13 9-46 cassette with a 1x system just fine.
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Old 05-25-20, 07:44 PM
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Wow, I never see the new Shimano components discounted like that. Where did you get the 20% deal and 12% rebate?
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Old 05-26-20, 06:40 AM
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Originally Posted by dwmckee View Post
Wow, I never see the new Shimano components discounted like that. Where did you get the 20% deal and 12% rebate?
Backcountry and Active Junky. I knew some good sales were coming because of the corona virus lockddown. I just waited until I was able to stack some discounts up before making my purchase. I was planning on waiting till the end of the year but with discounts and the real possibility of bike part shortages made me buy earlier than I wanted.

Ran into the same thing with Shimano XT 11-42 cassettes. Many online retailers are out of stock. Amazon went from 14 down to 4 available for sale in less than 24 hours. I just went ahead and bought that too for the same reasons. They're not sold out everywhere, but they are getting harder to find for sure.
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Old 07-20-20, 03:17 PM
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How about an update that nobody asked for?

My experiment with the Praxis crankset didn't work out. Turns out the M30 Praxis BB cannot be shimmed or modified in any way to help with the chainring and chainstay clearance issue. Even with the help of the Praxis guys it still didn't work out.

My solution for the problem was to install the GRX 815-2 crankset with a Wheels Mfg 386 Evo to Shimano conversion bottom bracket. Turns out the additional 2.5mm offset on the GRX crankset was just enough to get the proper clearance needed between the chainstay and the small chainring. Chainline is just about perfect too.

Also installed the Shimano XT 11-42 cassette. Definite improvement over the Sram.

A couple more detail pics:




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Old 07-26-20, 04:18 PM
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It is real nice to see people figuring out the things that GRX can do that Shimano says cannot be done. Ever since since the group was first revealed I wondered about 2x11 with an 11-42 cassette, no one could confirm it could be done, but you have clearly done it with the 1x specific rear derailleur and I've seen it done with the 2x 10 speed grx 400 rear derailleur as well, on an 11 speed drivetrain. I ended up going 1x on my bike, I am running a full GRX 800 mechanical group with an XT 11-46 cassette, another thing that Shimano says cannot be done but it does indeed work just fine.
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Old 07-26-20, 09:33 PM
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alot of their gearing limitations are due to chainstay length, they have to make sure it will work on the smallest frame. With a size 56, you can get away with alot more
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Old 07-28-20, 11:59 AM
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That is one clean looking bike. Not a fan of the big S but that's hot. Shimano really downplays the capabilities of GRX as a whole which is weird to me. I am running mechanical 800 with the 42t crank and the 11-46t cassette which Shimano says you can't do but the B screw had more than enough room to spare and honestly it might even clear the 10-51 but my wheels aren't micro spline to give it a try. Only downside I found is that no one makes a really long chain lol so I had to splice together 2x of them.
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Old 08-02-20, 04:25 AM
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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 just ordered an RD-R815 for my bike to replace the 8050 GS rear, so now my remaining ultegra component is the front DR which will stay because I have a 50/34 power2max crank. I also have to say, I much prefer the metalic pads to the resin pads that come with the GRX calipers, they are harder on the rotors but stop with less hand pressure and fade less too. I do like the position of the hidden buttons on the GRX Di2 over the Ultegra and DuraAce location, nice change that I would bet will come with any new version of Shimano Di2s.
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Old 09-02-20, 03:15 AM
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Quirks and issues with RD RX817 2 x setup

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 ...
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