Advice on cassette/RD mismatch
 

Got a question for the bike mechanics among us. I have a CAAD12/Ultegra with the short-cage R8000 derailleur. I recently replaced the 11-30 cassette with an 11-32, which is beyond spec for the short-cage RD.

It shifts fine and runs quiet on the larger cogs including the 32T. However, when up-shifting to smaller cogs, the chain hesitates and sometimes skips over a gear. The chain is new (DA). The bike's been to my LBS and I believe they've adjusted the RD to be as good as it can be, but it's still not ideal.

My thinking is that I need to install the long-cage R8000 derailleur to truly fix this issue. It's not that much money (around $85). Here are my questions:

1) Is changing the RD a likely fix for the shifting problem?
2) Do I need to lengthen the chain to accommodate the larger RD? Shimano's instructions say to measure chain length without the RD in the path, so this implies the choice of RD has no effect on optimal chain length.
3) When adjusting the replacement RD, I'm familiar with how to adjust the limit screws, the "B" screw (for height) and the barrel adjuster. Are there any other special things I need to know?

Thank you.

If it goes into the big/big OK, then the worst to expect is slight slack in small/small.

If the chain was too short, disaster would have already happened in the big/big, so it is long enough.

Checking the hanger alignment and cable/housing issues are standard for hesitant shifting.

Possible issues from new chain/older cassette that may settle after some miles.

You can also try a Wolf Tooth adapter rather than buying a new RD. It's a cheaper way to get the extension you need for a larger cassette.

+1

Eyeballing it will get you close, but Park Tool DAG-1(or similar tool) will help.

Hey, do those really work? I've got a Bianchi with 50/34 in front and 12-25 in back, and a short-cage Veloce 10sp. derailleur. I'd like to run a bigger cassette, but it would exceed specs.

I'm not having any problems when the chain is on the largest cog, so I'm not sure how an adapter would help. The issue occurs when shifting from a small cog to a smaller cog.