Bicycle Mechanics - Changing Cassettes

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jays35
05-18-09, 09:34 PM
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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!

Dave

bikeman715
05-19-09, 08:48 AM
check out parktools.com.,yes you'll need to add one link to your chain.
cincy_14
05-19-09, 09:31 AM
See Sheldon's article on the B-tension screw http://sheldonbrown.com/derailer-adjustment.html#btension and the section on chain length there as well. You may or may not need to lengthen your chain depending on how short it currently is in the big-big combination.

capwater
05-19-09, 11:20 AM
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.
jays35
05-19-09, 12:36 PM
Thanks for all the input!!!
Al1943
05-19-09, 02:29 PM
It's unlikely that you would need to add any chain. Check to see that you can shift into the big to big combination just in case you accidentally cross-chain.

Al