Originally Posted by MagicHour

With the 12-30T it's possible you may be exceeding your rear derailleur tooth capacity if it's a SS short cage type, although a guy in this thread says it works with no problems:
http://www.bikeforums.net/showthread...e-will-it-make

You could try it, or just stick with 11-28 since you know that works. Are you trying to lower your gearing? - because another option would be to swap out to a compact crankset if you don't already have one.