Switching cassettes
 

Should be a relatively easy answer, I'm sorry as I'm a newbie. 2011 Trek 1.2 C with a 50/34 crank and 11-26 cassette. I needed a little better ration for steep sustained climbing so I ordered a 11-30. I've heard this may need a new RD and chain. Is there any info I could provide you guys with that would help me determine that, or is there a chance of a straight swap if I stay away from the 50/30 combo.

Unless you have an 'GS' model RD, then you will need a new RD, virtually guaranteed you will need a new chain as well, as the current one will be too short (you can confirm this by measuring the old one with the new cassette fitted) if the current chain has a lot of distance on it / wear would replace anyway.

On the basis you are getting a Shimano 4500 11-30 cassette, there will be a big jump from the 26t to 30t, if you are climbing unloaded (i.e. just you and the bike) you may find you have lost some useful mid range gears and gained one very low one.

You could try it with the current derailleur and chain just to see if it would work. You will definitely have to screw the b-limit screw on the der all the way in. If you back pedal in the 30/34 combo and still hear clicking noise, or hear bad noise shifting from the second lowest to the 30t cog, that's the guide pulley at the top of the derailleur cage hitting the cassette teeth and you will need a long cage road derailleur, Sora GS.

If the chain is in decent shape and already comes with a quick disconnect link, you could merely sub-in a link or two with a second quick disconnect link to get the chain to the correct size. Buy that quick link from a shop and see if they have a short 9sp chain segment leftover you could have.

"if I stay away from the 50/30 combo."

Do not depend upon remembering to stay out of this combo to stay out of trouble. You will eventually forget and shift to that combo. If your chain is too short you can expect a damaged derailleur at minimum, possibly frame or other damage as well.

Make absolutely sure that your chain is long enough to comfortably shift to 50/30 or you will have an unpleasant surprise waiting for you some day.

Thanks everyone for the advice. I'll swap on a new longer chain when I do the cassette and I'm hoping to get away with the current RD. Time will tell.

Here's the setup guide for Sora 3400.

http://techdocs.shimano.com/media/te...9830614952.pdf

techdocs.shimano.com should be a mandatory bookmark for anyone working on their own bikes.