Hi all,

Sorry for what is likely an easy question. I have Ultegra Di2 R8050 - and just changed my cassette from an 11-28 to 11-30, which I understand is doable within the short cage rear derailleur hanger.

After changing, I can tell the alignment of the chain is just not "perfect" as it was before. 

Do I need to look at adjusting the alignment via adjustment mode, or is there something else I need to be telling the Di2 via the computer connection? 

I made the new chain the exact same length as the old one - which I assume is correct too, but please let me know.



hawkinspeter [4248 posts] 5 months ago

With the chain alignment not being the same, I'd be questioning whether the replacement cassette is installed correctly - either a missing spacer or an extra spacer would throw out the alignment slightly. Also, check how the wheel is installed to see whether it's slightly skewed or not (probably more likely if you've got QR skewers than if it's Thru-Axles, but worth double checking). Also, if you've got a new wheel, then that can affect the position of the rear cassette slightly.

If you're happy that the rear wheel and cassette are all good, then it's pretty easy to do the alignment using the adjustment mode (put the bike on a stand so you can spin the chain easily, hold down the Di2 junction box button until you get a steady red light and then the up/down gear buttons will perform micro-adjustments to the rear derailleur). This is probably a better instruction: https://pbandjcoaching.com/di2-secrets/

If you use the synchro shift modes, then it might be worthwhile using the PC connection and update the information about the new cassette so that the front derailleur shifts appropriately (don't know if just going from a 28 to a 30 will actually change anything though).

Pilot Pete [248 posts] 5 months ago

Also make sure the B screw tension adjustment is correct. Follow the Shimano Dealer Manual instructions. It could be that the top jockey wheel is now too close to the largest cog on the cassette.


r.glancy [31 posts] 5 months ago

Is it a Shimano chain? if so they are directional. The logos on the chain should be facing you. 

Also, The chain should be longer than your previous one, but not by much and you may get away with it the same length as with the 28t. 

How many miles on the chainset? as it also might be a case of the new chain and cassette needing to bed in. I have multiple wheelsets with the same hubs and they all sound different when I put them on due to the age of the cassettes. 

ashtons99 [3 posts] 5 months ago

I did it on mine ok. Just as a safeguard I set the synchro shift up so that if I was on the large chainring on the front and tried to shift up into the 30 it automatically shifted to the smaller chainring and dropped down a couple on the back. Works fine