hi!
i have a Shimano R9100 groupset 50/34 - 11/30
i realised that when i have small sprocket in cassete and in the crank , the chain makes a loop.
and when i have the large sprocket in cassete and the large sprocket in the crank the chain is too tight to change gear at the cassete.
i couldn't remove a link from the chain because it will be too short.

so what I did, was to change the b screw.

At the rear derailleur with a longer one and this fixed all the issues that I had,
now everything is working smoothly.



new longer B-screw

the installed new longer B-screw

loop at chain with original shimano B-screw

large sprockets and shifting works normal

with the new longer B-screw there is no loop

I hope this helps someone that had the same problem as mine
have a good day.

The longer screw probably shouldn't be necessary. I'd check that the derailleur is installed correctly. It's very common to miss the proper mounting tab on a Shimano shadow deralleur. The b-link as Shimano calls it should be more horizontal, not entirely, but more than that.

is the dura ace r9100 shadow?
I thought that this was only for the xtr mountain bike derailleur

It's every shadow derailleur, from the cheapest Alivio to XTR/Dura-ace.

I've looked at these pictures of yours mounted and compared them to others. Pretty sure it's not hanging on the proper mounting tab. You don't even have to fully remove it to check, just unthread the bolt most of the way. Can you rotate it back and get the little tab to hook over the derailleur hanger?

Even without trying to compare the angle of the b-link, the slack chain is exactly what happens if you miss the tab.

Looking at the lack of tension on your chain in the small small combo makes me shudder, please dont attempt to ride that out on the road, just shift to big ring, there shouldn't be chain droop even in that combination of gearing and it's really not a good idea to ride in small small anyway due to lack of tension even when there isnt the blackness shown in your photo.

Deraillieurs have a maximum capacity rating for a reason, if your choice of gearing means that you are outside of that range then you should change your deraillieur or change to a lower range cassette

Don't assume your rear derailleur was setup correctly the first time and have to install a longer screw. You should check it yourself, then make sure the B-limit is set correctly, then check chain length.

I have the same combo as yours except mine is R8000 series. B limit on mine was not set correctly and I had to remove two links on my chain. There is no issue shifting to any gear.

The derailer is not mounted correctly