Poor shifting just in 3 largest cogs

I have a shifting issue on one of my bikes. The issue seems to have arisen after changing to a new chain. I know normally poor shifting is a result of cable or derailleur issues, but I'm struggling to figure this one out. Shifting is great between the 8 smallest cogs (11-21 cogs) both ways. Shifting is really bad specifically when down-shifting (shifting away from the spokes) between the 3 largest cogs (28, 25, 23). Shifting back up towards the spokes is great. The issue is particularly bad if I'm in the big ring, but is still there in the little ring.

Bike is an Orro Terra Gravel. Groupset is full 105 5800 - compact chainset and 11-28 cassette. Chain is a KMC X11-93. I've used this same model of chain on this bike, so I know it can shift very well with the Shimano components.

Initially I thought it was the result of a chain that's too short. 54 links rather than 55. So I added another link back in to the chain this morning but the problem persists.

Here's what else I've done and checked so far:

• Removed cassette, cleaned, re-seated, and confirmed all cogs and the lockring are correctly seated on the freehub.
  
• Replaced rear mech hanger with a brand new one.
  
  

Anyone have any ideas?

Tonight I'm planning to:

1. Swap in another rear wheel that I know shifts well to determine if the issue is on the wheel/cassette.
   
2. If still an issue, replace the gear cable.
   
3. If still an issue, swap in another derailleur that I know shifts well.
   
   

Is there anything else I'm missing, or does anyone have experience fixing this type of issue?

B-screw means the jockey wheel is too close to the big cogs, this will cause rough noise or vibration when shifting around big cassette sprockets.

Bent derailler hanger or derailler means shifting ok some spots and bad others.

Also, size the chain correctly - wrap it around Big-Big without passing it through RD and then add two pins or another link (see park tools site for pics). Don't get your chain length.

I'd say almost definitely B screw. Wind that sucker in and get the jockey wheel away from the cogs and it will improve.
Had the same thing on my other half's bike. Would shift very poorly or not at all from the first 3 cogs, fine after that. B screw just needed adjusting

Thank you both! I'll make the B screw my first point of call to check this evening.

Check the inner gear cable at the shifter end.

The inner cable on my 5800 shifters has split/frayed there a few times, causing dodgy shifting.

@hazzelfrazzel

as per @farewell 's suggestion - shift into lowest gear at the rear and get the chain onto the lowest gear sprocket. then without pedalling shift into the highest gear to release the gear cable, this will hopefully give you enough slack in the cable to be able to push the cable through the shifter and you may be able to see if the cable is frayed inside the shifter

also sometimes when you fit a new mech hanger it may need a little tweak to get it to sit parallel to the plane of the wheel.

does the mech show any signs of crash damage - is it scuffed at all, it could be that the mech is bent (not just the hanger)

or new bike time or upgrade to di2

and make sure the loop of cable from the frame to the rear mech is long enough. If its too small it'll be adding friction in the cable

if it's too long it could also be adding friction

Aaand the issue was the b screw! Tightening it up a bit moved the jockey wheel away from the bigger cogs and the issue has gone away.

Thanks, all!

Yeah, I've had this happen on 5800 levers too. Seems to be a bit of a design flaw.