I want to change my 12-25 to a 12-27 for some upcoming rides that have several hills. WIll I need to add a link(s) to my chain? What or how much clearance should there be between the largets cog and the idler pulley? I currently have Shimano's, 105's on the bike and will probably go back with 105's. Any web sites that you might recommend?
Thanks in advance!
I have never had a problem swapping between 23, 25 and 27s. Often do it when going to the mountains for the day. So long as your chain is sized correctly, ie it wasn't cut very short, you should have plenty of clearance. If your RD is set up right the b screw shouldn't need to come into play.