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Researching an upgrade to GRX Di2, am aware from this forum (as well as Shimano) that the GRX 2x crankset is pushed 2.5 mm outboard and thus requires a GRX FD. However, what about the opposite: using a GRX (Di2) front derailleur with an existing Ultegra 2x crankset that came stock on a 2020 Trek Checkpoint SL6?

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  • Hi did you end up using GRX front with road crankset? Did you add additional spacers or anything? If so, what are your experiences? Oct 22, 2021 at 21:18
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    This is the reverse of this question Oct 23, 2021 at 0:24

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Is there any particular reason you want to mix FC-R8000 cranks with a GRX Di2 FD-RX815-F front derailleur? the Ultegra Di2 FD-R8050 will get along just fine with GRX Di2 rear derailleur as Di2 sees it all as part of the road family.

the GRX front derailleur, including the Di2 FD, is shifted +2.5mm outboard to match the GRX cranks. I would not count on it working with your Ultegra crankset. that being said, depending on where the frame manufacturer's actual braze-ons lie relative to Shimano spec, the chainline issue may or may not work. unless you've bought smaller chainrings for your FC-R8000, however, your large chainring is too large for the FD-RX815-f, which is designed for a 48T max. if you have purchased the Ultegra 46-36 chainrings for cyclocross, you'll be even further from the 17T capacity of the GRX front derailleur, so I'd treat the front drivetrain as a package deal, and if you must buy one before the other, maybe buy the crankset first.

There was a post on the S-Tec (Shimano bike shop employee site) community forum where a user said that on his Di2 equipped Trek Boone, he was able to get the GRX crankset to work with his old (non-GRX) front derailleur. I wouldn't expect it to work as well in the opposite direction, but the location of the FD braze-on on the Checkpoint might be slightly different one way or the other.

According to a post from 9 months ago on the S-Tec forum, you could even use the RD-RX-817 with a front derailleur, albeit with some limitations, and no official word on "whether or not that will be 'fixed' in a later patch."

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  • Thanks for the detailed response. I was aware of the 2.5 mm shift but had not considered the 48T limitation using the FD-RX815-f. Will proceed with Di2 FD-R8050 and keep front all Ultegra. I heard recently of one rider's issue with his Ultegra Di2 FD "failing" due to the harsh environment of gravel riding. It made me wonder if GRX would be superior to Ultegra when used in the harsher environment of gravel riding. But not enough to want to give up the FC-R8000 crankset since the Checkpoint does double duty as my gravel and road machine. Mar 24, 2021 at 1:44
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In truth, a GRX front derailleur WILL definitely handle 50/34 Dura Ace or Ultra 2x cranks. Look at any photo of A. Vermuelen’s gravel bike he used at SBT this year. That is clearly a GRX front derailleur and a 9100 Dura Ace crankset.

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    Welcome to Bicycles SE. SE sites do not function like a typical chat forum. Your answer is more of a comment (when you garner enough reputation you will be allowed to comment on an answer or a question). In the mean time, please do two things: 1) add the documenting photos that you claim to exist to your answer (by editing it and including a photo or photos) in order to defend your answer, and 2) change. your. tone. of your answer. Without additional documentation and if the harsh tone and criticism does not get scaled back, this answer will likely be flagged and deleted.
    – Ted Hohl
    Nov 13, 2023 at 21:03
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    @TedHohl I think it gives a good alternative answer citing a real world reference. Perhaps it should be expanded but it is not a "comment"
    – Noise
    Nov 14, 2023 at 9:46
  • @Noise I could see that it had some "answer" in it (and I could see how it could have some usefulness in it based on my limited experience in the same area). Thanks for the insight and the observation. The lead in is a bit harsh as this is not a chat forum. I will edit out the criticism of first sentence and leave the answer as it sits. For the answerer: Tact and tone matter, otherwise the content degrades. We have voting in place to apply criticism to answers/questions that are inappropriate, off-topic, or wrong.
    – Ted Hohl
    Nov 14, 2023 at 15:32
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    @TedHohl you do alot of work Ted, good stuff, but you are tough on people! Tact and tone matter!
    – Noise
    Nov 15, 2023 at 16:30
  • @Noise I appreciate the feedback. I am hoping that I am giving good guidance for a new poster to learn the ABCs of a good question/answer. Everyone has some value to add here, even when it may be obscure to some. I try to keep an optimistic view of all the input.
    – Ted Hohl
    Dec 7, 2023 at 4:07

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