adjustments when changing cassettes

I think all you really need to do is make sure you chain/derailer will support a 12-27 and then your derailer will need to adjust the B screw I think it is called.  So that the gap from you derailer to the cassette is correct.  I would think the limit screws would be okay since the cassette is not any wider.

As long as your chain isn't worn, you shouldn't have to adjust anything. I swap back and forth between a 12-21 and 12-27 with no problems.

scott

That ws going to be my advice, wait until you see if any adjustment is neccessary, if so, make sheldon or park tools web sites your freinds.

I have switched out a couple of cassettes and not needed any adjustments.

Sometimes you do, sometimes you don't. Not sure what contributes to it, but if you DO need to adjust the "B" screw:

http://bike.shimano.com/media/techdocs/content/cycle/SI/Dura-Ace/RD...

You will if your cage and pulleys get pulled too far out of plane and your chain starts skipping. 25 to 27 is NBD so I'd bet you're OK.

maybe my chain is too short because I seem to have a problem running/shifting my low gears and the derailreur sure looks like it is in pain all stretched out. My LBS told be my chain length would be fine, but it sure seems like that is my issue