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Hi

Currently have a 7 speed and looking at various options, and possible 'migration' paths.

I've seen some posts where I could apparently run a 9 speed derailleur (shimano, or SRAM) on a 7 speed. Naturally, would need the shifters to match :D. I'm mainly interested in the 9 speed rear derailleurs for the better/higher spec levels available.

What's not mentioned is what chain would/should be run. Would putting a 9 speed rear derailleur mean I should use a 9 speed chain? Would that be likely to cause any issues with the 7 speed cassette? Or would I use a 7 speed chain, and would that cause any issues with the rear derailleur?

TIA
db
 

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Not sure if I misunderstood what you wrote, but you won't want a 9-speed shifter if you'll be keeping the 7-speed cassette/freewheel. Just switch out the derailleur and everything should work fine (after being setup properly, of course).
 

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Ditto on keeping the 7 speed shifters. 8 Speed cassette spacing is even slightly different enough that 8 speed shifters won't work perfectly with a 7 speed cassette. 9 Speed won't work right at all.

Drew
 

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FYI, you will not be able to run a Sram derailleur with any 7 speed shifters. They use a different leverage ratio than anything that was available for 7 speed. You can use Shimano 9 speed derailleurs fine, but make sure they are the 9 speed stuff. When Shimano went to 10 speed they also changed their leverage ratio so their new shifters won't work with their older stuff.
 

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FYI, you will not be able to run a Sram derailleur with any 7 speed shifters. They use a different leverage ratio than anything that was available for 7 speed. You can use Shimano 9 speed derailleurs fine, but make sure they are the 9 speed stuff. When Shimano went to 10 speed they also changed their leverage ratio so their new shifters won't work with their older stuff.
Can you elaborate? My wife's Trek Navigator had a SRAM derailleur and it came with a 7-speed freewheel and SRAM shifters. When I replaced the derailleur with a Shimano LX I had to replace the shifter because the ratio is different, but I could have gotten a new 7-speed SRAM shifter that was compatible with the SRAM derailleur.
 

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Sorry about that...my fault...I didn't see your comment about needing shifters to match! :madman: ( I guess I need to learn to read more thouroughly.)

I thought your initial comment/question was adding a 9 speed derailleur to an older drivetrain.

Anyhow, as long as your leverage ratios match, there is no reason you can't mate a 9 speed derailleur to a 7 speed shifter. Heck, when Shimano first came out with 9 speed, I used an old 7 speed XT rear derailleur with 9 speed shifters/cassette and it worked fine (I realize it is the opposite of what you're asking, but it shows that it works going either way).
 
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