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Old 05-31-09, 09:10 AM   #1
Zaphod Beeblebrox 
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9/10 Speed Derailleur on 7 Speed Cassette?

I have Shimano 7 speed index shifters, a 7 speed shimano hyperglide rear hub and Cassette. Can I use pretty much any Shimano index compatible Rear Derailleur, like a 8 or 9 or 10 speed or do I need to look for a "7 Speed" Rear Derailleur?
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Old 05-31-09, 09:21 AM   #2
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I'm not an expert on index systems, but I know they are pretty finicky about compatibility. Interchanging parts between different speeds will cause indexing problems. If you want to assure index shifting, better to stick with the same model.
There was a thread some time back about this compatibilty issue and interchanging speeds/components. Alot has to do with chain width and gear spacing on the cassettes. Do a "search".
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Old 05-31-09, 09:47 AM   #3
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Quote:
Originally Posted by CravenMoarhead View Post
I have Shimano 7 speed index shifters, a 7 speed shimano hyperglide rear hub and Cassette. Can I use pretty much any Shimano index compatible Rear Derailleur, like a 8 or 9 or 10 speed or do I need to look for a "7 Speed" Rear Derailleur?
I don't use indexed systems either, but no.... it doesn't matter. Shimano, Campy and the like have not yet figured out how to make their "system" so totally specific so you need a new rear D for every change in cog set or other components .... yet!

I'm glad I stuck with friction
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Old 05-31-09, 10:08 AM   #4
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Yeah I'm a friction guy myself, and this is my first time putting together Index shifting... It seems like I've seen eBay listings for 7/8 Speed RD's so I kinda assume that is cool to do but I'm looking to find out what will work so I know how wide of a net to cast so to speak on ebay.

I was sorta under the impression that the most important thing is that the Shifters and the Cassette were the same make (Shimano) and same number of speeds, since the Indexing is in the Shifters, not the Derailleur...but like I said this is my first time so I wanted to check in with yous guys.

Thanks!

**edit**

Did some searching and I think I found what I need.

7 Speed shifters and any Index compatibe RD seems to be the consensus.
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Old 05-31-09, 10:18 AM   #5
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I have a 9spd Deore rear derailleur with a 7spd cassette on both of my Trek bikes. Works great.
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Old 05-31-09, 10:28 AM   #6
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Originally Posted by CravenMoarhead View Post
7 Speed shifters and any Index compatibe RD seems to be the consensus.
Yes. Except for pre-9-speed (1997) Dura Ace, all Shimano indexed rear derailleurs have the same cable-pull ratio/geometry. As far as number of gears compatibility, if the number of gears in the shifter and the cog match, then the derailleur will go wherever it's told to.

Other factors you should consider:
-Chain wrap capacity: determined by the length of the cage--between the two pulleys--so that with the proper chain length you can use the bib chainring/big cog combo and still use the small/small combo without the derailleur folding into itself with no tension.
-Max cog capacity: so it can work with the size of your larg(est) cogs.

In general, for Shimano RDs:
-Road SS: double chainring, 27T or smaller cog
-Road GS: triple chainring, 27T or smaller cog
-MTB GS: double chainring, 34T or smaller cog
-MTB SGS: triple chainring, 34T or smaller cog
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