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The middle chainring on my bike needs to be exchanged and I can't find a dealer that carries the parts or would even be able to order them from their wholesaler. From all I can tell my crankset is an FC-7900 (manual here) and the chainring in question is a 42T, and I have been able to find these online, but only with differing teeth numbers.

Is my understanding of the manual correct that both 39T and 44T chainrings would be compatible with the sprocket that currently has a 42T mounted?

Thanks for all answers! :)

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    When you use the phrase 'middle chainring' people will usually assume you are running a triple. The manual you linked shows a double.
    – Andy P
    Commented Jul 7, 2023 at 10:51
  • The 7900 groupset may not have had a triple at all. 7800 and 7700 did, but by 7900 we had compact cranks.
    – Weiwen Ng
    Commented Jul 7, 2023 at 15:36

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According to this table from the exploded view:

enter image description here

The only overlap is that a 53T big chainring can be matched with either a 39T or a 42T. Notice though that the part number and the type of the 53T chainring is different (A-Type when matched with 42T and B-Type when matched with a 39T) so they may not be interchangeable.

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