Replace Ultegra 12-25T with 105 12-27T ?

josehernandez

Can I replace my Ultegra 12-25T cassette with a 105 12-27T without having to worry about new chains or extra links ?

john-e-big-guns

New block= new chain...if the block is quite new and not much wear ya should be OK...but if is an old chain/block with wear ya will have problems

smidsy

Quite probably, certainly the rear mech will normally take it.

Chain - depends how short yours already is, but normally not an issue as you should not be in 50/27 anyway :-)

drlodge

smidsy wrote:

Quite probably, certainly the rear mech will normally take it.

Chain - depends how short yours already is, but normally not an issue as you should not be in 50/27 anyway :-)

+1, it SHOULD be straight swap.

greentea

I recently replaced a 11-28 cog on an Ultegra rear with a Tiagra 12-30 cog and the chain didnt need replacing or adjusting at all. The rear derailleur was an Ultegra s/s.

You should be fine. Try it first, then if its really bad change the chain afterwards, but im guessing you wont need too.

The only thing you might need to do is screw in the B-screw a little bit, on the rear derailleur, to give you a bit more clearance between the small cog and the largest gear (27) but again, might not even be needed.

josehernandez

What adjustments would be required if I change from 12 - 25 to a 11- 28T ?

bus_ter

possibly a slightly longer chain. As said above I would ideally be looking to change to chain at the same time, so you can resize the new one. Be aware that Shimano document a different way to measure up an 11-28 chain length than with a smaller range cassette.