Originally Posted by
Barrettscv
You should shorten the chain.....
No. See DaveSSS's posting for the reasoning. In this case the derailleur's chain wrap will have been exceeded and a chain short enough to allow small-small will not accomidate big-big. That could lead to severe mechanical damage if big-big is used even inadvertently.
Originally Posted by
Barrettscv
...and add a "Dogs Tooth" as a guide to keep from dropping the chain to the inside.
Agree fully. A Deda Dog Fang, N-Gear's Jump Stop or a Third Eye Chain Watcher should be fitted for the reason you give. I recommend one of these for any triple set-up and particularly when the stock granny chainring has been changed for a smaller one. Very cheap insurance.