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Shimano 2X GRX - Chain length Question

Old 11-25-22, 04:25 PM
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Steve_sr
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Shimano 2X GRX - Chain length Question

Hello,

I am working on putting together and adjusting a Shimano 2X GRX system. According to the Shimano documentation for the rear derailleur they are specifying a 4-6 link overlap in the big-big combination. That didn't work out... too loose on the little-little combination. Below are photos of the current state with about 3 links of overlap.

The rear derailleur link will actually fit in 2 positions. The current position is per the install instructions but it will also fit the hanger mostly vertical. So is the chain still too long? I am hesitant to keep taking links out two at a time as I don't want to end up with a chain too short to go into the big-big combination

On a separate but related question the front shifter appears to be a 4 position lever. Is the "L-trim" (bottom) position not used or is it just not adjusted properly yet? Again I followed the instructions in the documentation.

Thanks,
Steve



Little-Littler Combination


Big-Big Overlap


Big-Big Combination
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Old 11-25-22, 04:38 PM
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Polaris OBark
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This has a good description. Look toward the bottom of the page:

https://bettershifting.com/installat...and-direction/
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Old 11-25-22, 07:58 PM
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Originally Posted by Polaris OBark View Post
This has a good description. Look toward the bottom of the page:

https://bettershifting.com/installat...and-direction/
Nice website! I wonder where the graphics came from. It is a much easier method to use the big ring to hold the chain in place. However, it directly contradicts Shimano's own documentation for the RX-810 rear mech. The website lists GRX under BOTH Shadow and MTB which are different.

My setup is quick link +4. I also think I found my problem... The infamous "B" screw was still too loose to tighten the chain in the L-L combination.Based on the previous photo I don't think that I need to take any more links out. Do you?

Thanks,
Steve
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Old 11-25-22, 09:05 PM
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It is a great website, and made setting up my wife's bike with Di2 much more straightforward.

I used his instructions for setting up her chain, and here is how it looks:



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Old 11-25-22, 09:09 PM
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I think the graphics are from Shimano. But this site is much more user-friendly for the most part (I think he added the GRX stuff on as a revision, so a little less so in this particular case).

I now remember that the B-screw adjustment was critical and I even made a post here (somewhere) asking if I had it wrong and the derailleur hanger required a direct mount (it didn't).

That's an 11-36T cassette, in case it looks odd.

I should add that it shifts flawlessly, and it sure looks about the same as what you have. I would not take any more links out. The default Di2 setting prevents you from going into the smallest and penultimate cogs on the cassette, so my guess is they would advise the same shifting pattern for conventional cable shifting.

Last edited by Polaris OBark; 11-25-22 at 09:12 PM.
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Old 11-25-22, 10:39 PM
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I like the small/small method....
I have used it with modern 50/34 11-32 setups and vintage 52/39 12/28 setups
have not tried with GRX, but don't see why it would not, if gives the greatest possible chain length while avoiding bib/big not working, which is key

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Old 11-25-22, 10:50 PM
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what deraillers, crank and cassette are being used?

from what I can tell 2x needs the RX810 which is 34 teeth max rear cassette and 11 too min rear, with a wrap capacity of 40 and max front cog difference of 17 do if OP exceeds this where will be issues

the RX812 works for 1x11 setups not 2 x
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Old 11-26-22, 04:44 PM
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Originally Posted by squirtdad View Post
what deraillers, crank and cassette are being used?

from what I can tell 2x needs the RX810 which is 34 teeth max rear cassette and 11 too min rear, with a wrap capacity of 40 and max front cog difference of 17 do if OP exceeds this where will be issues

the RX812 works for 1x11 setups not 2 x
It is a full 810 2x setup with 11-34 in the rear. Everything should be compatible
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