kfjatek wrote:If you put a larger big sprocket, wouldn't you need to readjust the B-tension screw on the derailleur (to give the chain enough space)? Also - perhaps the H / L screws need realigning?
There's a good video here that could help: http://www.youtube.com/watch?v=CPLiW-0zLa4
Ah, I did wonder if that might be the case. Bike shop it is!