11-30 on Ultegra short cage

[qtrpounder]

Hi, advice pls: currently running an 11-25 Ultegra 6800 with a short cage derailleur. Is it possible to change the 11-25 out for 11-30 without too much hassle (like new chain or new derailleur/cage)? Thanks

 

[Ajax Bay]

If the chain is currently the correct length, you will need a new chain at least one (inch) link longer. (Note that if you installed a new 11-25 cassette you'd need a new chain anyway.) It may need to be 2 (inch) links longer. Chain round large/large (not through RD cage) plus one inch link is the way I do it.
You are asking the RD to perform outside its specification, but many on here have managed that. Some B screw action will likely be required.

 

[si_c]

Shimano say 28t max on the RD-6800-SS, but usually you can add a couple of teeth without difficulty. As @Ajax Bay says you will likely need a longer chain if you do opt for the 30t cassette and you'll need to watch the derailleur position on the largest sprocket - if it's touching the cassette then you need to wind out the b-tension screw.

 

[Kestevan]

You can even go to 32 with SS, but at that point I really didn't feel comfortable with the positions when cross chaining either extreme (not something you should be doing anyway really).

It struck me as a potential accident waiting to happen if the chain was cross chained at speed or on a rough road, so went with a GS cage on Mrs Kes bike last year.