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Hello everyone I recently broke my Derallieur in my Road bike and I am planing to get a new one online but I dont know exactly wich one to get is for the rear Derailleurs of 7 speeds. thanks

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Can you read the model and/or brand of the current one? Barring that, model/brand of bike and some pictures of the current derailleur? – Ken Hiatt May 31 '12 at 19:21
The age of the bike would also be of use. And is this an indexed shift or an old friction shift setup? – Daniel R Hicks Jun 22 '12 at 20:54

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Pretty much it doesn't matter - as long as the derailleur is comparable in brand and general "shape". The derailleur doesn't really care how many gears you have! The two things that have to be the same as (or compatible with) your old one:

  1. Cable pull ratio - each "click" of your shifter pulls the cable a certain amount, and the derailleur has to move by the correct amount per click. So - if it's a shimano, get a shimano, and you'll probably be OK.

  2. Capacity - if your largest tooth cog in back is a 32-tooth, no way is a "short cage" derailleur going to handle it. On the other hand if your largest in back is 23 tooth, a "long cage" would work but would look VERY SILLY

So, with several caveats to boot - as long as it's the same brand (or compatible), and approximately the same physical dimensions, it should be fine; 7, 8, 9 speed really doesn't matter. Post a close-up photo of the broken derailleur where we can read the model numbers/etc. and see the thing, and we'll give you a link where you can buy a replacement from :)

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Depending on the age of the bike there can be major differences in derailers for a 7-speed. Used to be that 7-speed was the max, and indexed at the same rate as 5/6 only with a wider axle. Then the pitch of sprockets changed -- several times. – Daniel R Hicks Jun 22 '12 at 20:54

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