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I currently have a 7 speed cassette, 7 speed derailleur and 7 speed shifter from Shimano. Unfortunately, my rear derailleur (Shimano Tourney) broke, so I want to replace it with something better. The problem I'm facing though is that I'm finding only 9 speed derailleurs that fit what I'm looking for and where I don't have to pay stupidly high shipping fees (I was looking at the Shimano Alivio line).

That's why I'm wondering if a 9 speed derailleur works with a 7 speed cassette and shifter. Would it work with the chain I have right now or does a derailleur only work with chains rated for the same amount of gears?

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  • Have you tried sourcing 8-speed derailleur. Pretty sure that will work fine. Commented Sep 12, 2016 at 15:27
  • I thought 9 speed derailleurs are not compatible with 7 speed because the chain sizes are different. Commented Aug 10, 2020 at 7:32

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Yes, all 9-speed Shimano rear derailers share the same actuation ratio as all Shimano 7-speed ones, except for pre-7700 Dura Ace.

I've never seen a 7-speed chain rub inside a 9-speed RD cage. If somehow that were an issue, an 8-speed chain would work fine.

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  • Theres basically 1/128" of width difference, and you need a bit more tolerance to have the thing work reliably. Commented Sep 13, 2016 at 4:23
  • I can verify this since I am running a 7 speed freewheel with an Alivio RD (9 speed) with a 7 speed chain on my commuter bike. Commented Jan 24, 2017 at 8:08
  • I thought 9 speed derailleurs are not compatible with 7 speed because the chain sizes are different. Commented Aug 10, 2020 at 7:32

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