DA 7800 rear mechanism + 30T cassette?

[polishbiker]

Hi

Need some advice, had a 10 speed dura ace 7800 groupset for quite a while, with a standard crank 53/36.
my cassette and chain need replacing, been running with a 11-25 so up to 23 usable while on the big sprocket.
i want to make my life a bit easier and get an ultegra 12-30 cassette and chain, the only thing is 7800 rear is meant to support up to 27T cassette.

so, does that mean i would also need to get a 10 ultegra rear mechanism for this to work? 6700 supports up to 30T cassette.
would my 7800 front mechanism work ok with such setup?

thank you for your feedback

[Duck!]

You will indeed need to replace your derailleur with a newer Ultegra or 105 model (but must be 10-sp, the 11-sp. models are not compatible with older shifters) in order to fit a larger cassette, the 7800 simply does not have the jockey wheel clearance to go bigger than 27T.

Your chainrings will be 39/53, 7800 Dura-Ace was never offered with smaller than 39T.

Your front derailleur will be fine with the larger cassette & 105/Ultegra derailleur.

[Blakeylonger]

I ran a 30t on my 6600rd and a 48/34 with no problems and no extreme b screw antics. Your individual situation may vary and a 6700a might be needed.

[polishbiker]

Thank you for the input

[Duck!]

Dura-Ace typically has much finer tolerances than the lower groups. I have never met a 7800 that will happily accept larger than its factory-stated maximum 27T sprocket (but will reluctantly accept 28T), but cheaper models can have the boundaries pushed a bit.