Old 10-01-20, 11:57 AM
  #4  
dsaul
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The Advent 2x9 rear derailleur has a capacity of 47t, so you will have enough capacity for the 46/30 front the 11/42 rear. The 1x9 rear derailleur only has a capacity of 41t and is not designed for the extra capacity needed for a double front chainring. As far as the chain length, that depends on the length of the chainstays on your bike, but any standard 116 link chain should be long enough.
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