Okay I’m having trouble getting my front mech set up correctly. No matter what I do the chain runs somewhere…
It’s the 8050 version and it has one bolt for adjusting. I’m not used to this.
Also, the rear tail of the front cage is too far out. It keeps getting caught on the teeth of the big chainring when in the big ring.
Any tips? Or should I just bring it to a shop.
There’s a hidden bolt on those too:
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When I changed chainring sizes, I used the installation guides at
https://bettershifting.com/grx-fd-rx815-ultegra-fd-r8050-dura-ace-fd-r9150-di2-front-derailleur-installation-guide/ and
https://bettershifting.com/set-up-front-derailleur-limit-screw-adjustment-bolt-one-bolt-derailleurs/
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So I take it the little plate may solve my issue
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So I take it the little plate may solve my issue
The correct hidden bolt setting pushed against the plate, maybe. It depends. FDs can be real MFers. 
Yeah I wish that solved my issue. I want to use all my resources before I go to a shop. And I don’t want to break it because I “believe the braze on mount is wrong”
Because eventually I might get there 
https://si.shimano.com/pdfs/dm/DM-R8050-01-ENG.pdf
That is the dealer manual.
If you cannot set it up following that, take it to somebody that can before you break something.
This is literally a 10min job.
If the ‘rear tail’ of the FD is out too far then that could be caused by a support bolt that is screwed in a bit too far… this is what pushes the tail of the cage away from the frame.
Also, Di2 derailleurs are a bit more fussy when it comes to the correct height, so I would double check that too.
But yeah, FDs can be tricky if you haven’t done it that often. If the problem persists I’d take it to a bike shop and ask them to check it while you’re watching. It shouldn’t take them that long.
Okay so continuing issue here. The big ring rubs the rear of the cage, if not stops it front rotating when I try and shift to the big ring. I’ve never had this problem before. Is there something wrong with my braze on hangar or is there some magic thing I’m not doing?
My front rings are 55-42. New build and I’ve never had this issue with my old FDs.
Frustrated
Is your derailleur set too low? Some derailleur hangers won’t go high enough to clear a 55t ring, especially on bikes that are optimized around compact chainrings.
If this is my issue, that’s not good, I had this frame before with no issues.
If I’m gathering your comments correctly, it’s not the lateral adjustment that is causing rub, but rather the vertical (up/down) that is causing an issue. In this case, I’m also assuming that only the back is catching, but not front (i.e. the front clears the ring).
The first and most obvious check is to make sure your derailleur is mounted as high as it can go.
The second check is to see if there is any ‘tilt’ adjustability in your braze on mount. If your braze-on FD mount is screwed on (not riveted on), some manufacturers (like Cervelo, giant, etc…) build in a bit of play in one of the FD braze-on mount screws so that you can adjust the tilt (up/down angle of the FD) for different sized chainrings.
Failing both of the above, I’d suggest you start posting pictures of your issues so that we can get a better sense of what is going on.
I will put up some pictures.
It’s a Felt IA, 2020.
I have never had an issue with 55 on my old IA bikes… so this is a weird problem. If there was a spacer or tilt I could use, the front of the cage would line up, raise the rear of the cage and actually clear the big ring! I can get it to be above the teeth, until I tighten the bolt down.
This is a super simple deal. If you have the FD raised all the way and the 8050 FD still hits your 55T then you can’t run a 55T. That simple.
The Di2 FD’s are absolutely dead reliable and once tuned (10 minutes with a manual max) never…ever come out of adjustment. I bet I have 75,000 miles on the Di2 FD’s without a single goofy shift. And I use synchroshift almost exclusive.
But the key is you have to be using parts that are compatible of course 
This was my worry!
So that means I’m limited to a 50t only? Is 53 too big ?
54 might work.
I know on the Trek Madones they “say” max is 54.
I also know that just because they “say” something won’t work doesn’t mean it won’t work. I’ve had great success with incorrectly sized rings / cassettes. But dealing with a mechanical stop like in your situation is pretty black and white! It’s either custom fabrication with a dremel type tool to slot your upper mount limit…or buy a smaller chainring.
Looks like the FD braze-on mount of the felt IA is riveted in place, so no tilt adjustability there:(.
In that case, I agree with the other poster who says your solution is simple: No 55t chainring for you. Looks like you’re running some pretty big gearing and you might have to make some concessions to go to a 53/39 or 54/x.
You might be able to get away with either the good ol’ sram mtb front mech wedge, or a spacer block for osymetric rings to raise or tilt your mech away enough
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The problem is the 8050 ultegra doesnt allow for a 55t chainring. But the old 6870 did. So I have to get a Dura ace 9150 derailleur because it allows for a bigger 55t chainring.
This was my worry!
So that means I’m limited to a 50t only? Is 53 too big ?
No.