I was wondering on a mountain bike what rear derailleurs work if have a 21 speed bike.

Additional information: 7 ring rear cassette and 3 in the front

Will an 8 and 9 speed rear derailleur work or how would i go about this getting a rear derailluer in that condition?

  • What brand are the shifters (or the existing derailleur)? – Batman Sep 16 '16 at 23:18
  • Can you post a photo of the derailleur? The way the derailleur mounts will make a difference. Are you sure you have a 7 speed cassette or a 7 speed freewheel? If you aren't sure search "Do I have a freewheel or cassette" in the search box at the top of the page. – mikes Sep 16 '16 at 23:44
  • I cant post photos no camera and it is cassette just simply wondering if the speeds can go back of 8 and 9 speeds can work with a 7 chainring cassette – Joey Sep 17 '16 at 9:41

I would say any 8 or 9 speed will work (same brand), you just need a 7sp shifter. The pulling ratio is controlled the by the shifter, so as long as the shifter has the same number of speeds as the cassette you should be ok.

  • Not categorically true. This answer for example could lead someone to try pairing a 1:1 SRAM derailer with their SRAM MXR Gripshift. – Nathan Knutson Sep 24 '16 at 1:39

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