Joined: Jul 2014
Posts: 1,397
Likes: 169
From: Milton Keynes, England
Bikes: 2.6kw GT LTS e-tandem, 250w Voodoo, 250w solar recumbent trike, 3-speed shopper, Merlin ol/skl mtb, 80cc Ellswick
Extensions can cause poor shifting, as it reduces the angle/force of the chain against the next cog, due to the jockey being further away.
It's important you use a cassette within the rated range of the derailleur, and adjust the B-screw accordingly, so the jockey is the correct distance from the cassette rings.
Your derailleur has a switchable clutch, you need this in the 'on' position when in use, only off when working on the bike.