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10sp Derailleur with 9sp Shifters and Cassette?


philip.maree
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My 9sp derailleur needs to be replaced sometime and I was wondering if I can buy a new SRAM X.0 10sp Derailleur and use it with my 9sp shifters and cassette? I am in the process of converting to 10sp but I was hoping to doing it in phases.

 

My logic tells me that the derailleur will only move as far as what the shifters are able to pull the cable. And that with the limit screws I will be able to ensure that it doesn't shift to far.

 

Is this logical?

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Apparently not, the cam design is slightly different, which leads to a slightly different pull ratio on the 10 speed derailleur.

 

I am open to correction, but I think thats the case.

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I think it could work. My reasoning being that the derailleur will do what the cable tells it to do so providing both the shifters and cassette are 9 speed the movement of the derailleur should correspond. I won't put money on it though, maybe Johan can help?

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on a roadbike it makes no difference as the shifters are the intelligence and the derailleur "dumb". I put 10-speed STI's on my old 9-speed bike and it worked perfectly. Would think mtb dr would be the same?

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I was thinking that the action ratio is 1:1 for both 10sp and 9sp derailleurs and shifters, therefore it should work.

 

If the pull ratio is the same then you're good to go.

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It should work - the cage should be the same size = same pull ratio.

 

Normally newer rear derailers are 8,9,10 speed compatible (for road at least). The derailer is just a slave to what the shifters make it do.

 

Just 7 speed and lower won't work - I tried upgrading a 7 speed to 8 speed - derailer didn't work, so got a new one :D

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on Shimano the derailleur for 10 speed is the same as the 9 speed, it's the shifters are different.

 

I am not sure on SRAM though...

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