I am looking at something like SRAM GX 2x10 MTB Rear Derailleur. Will it work with 3x MTB?

3 Answers 3


Yes, a long cage 2x10 GX RD will work as long as the largest cog on the cassette is less than 36T and the max teeth capacity is 47T. You can work out max teeth capacity by:

Chain capacity = (biggest cog teeth – smallest cog teeth) + (biggest chainring teeth – smallest chainring teeth)

Yes, it will work. Your front chainring / derailleur setup does not limit your rear derailleur options. Things to consider:

  • Chain length. You might need a new chain.
  • Chainline.
  • Gear range. Choose it wisely according to your needs and riding style.

Just checked SRAM website and it is indeed called 'SRAM GX 2x10 MTB Rear Derailleur'. Not sure why. Should be just 10 speed GX



It will undoubtedly work on the middle front ring and one of the others. It also depends on the design of your bike. I suggest you read about chainline. Here is an excellent description on Sheldon Brown:


  • 1
    If it will only work with 2 front chainrings (not all 3) then you should explain why, and how to decide which to make it work for.
    – DavidW
    Commented Dec 1, 2021 at 15:40
  • In the days when 3x were popular you'd get the same frame with the same RD either in 2x or 3x. (Later when 10 or 11 speed and wider gear spreading arrived on the market, 3x became unnecessary.)
    – Carel
    Commented Dec 2, 2021 at 8:46

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