I currently have a Tiagra HG50 9 spd 12/25.
http://bike.shimano.com/media/techdo...9830608763.pdf
I want to get a little lower gearing and I thought about a HG80 11-28.
http://harriscyclery.net/itemdetails.cfm?id=732
I don't think there should be a problem, but I am still confused about the 11 tooth. Does it use a different lockring?