# How do I know which front derailleur to buy?



## naiku (Apr 17, 2009)

I am looking for a new front derailleur for my bike, but am not entirely certain which I need that will fit my frame. I have a 2009 Rockhopper, currently it has a "Shimano Altus, 34.9mm clamp, top swing"

Now, I can find plenty of 34.9mm derailleurs, but I see high clamp, dual pull lo clamp, top pull, low pull etc. I believe mine is a bottom pull? so would I need something that is either dual pull or bottom pull, and then I get into the high or low clamp? 

Then I get into things like 2x10, I always thought front derailleurs were pretty standard in that it would not matter, 2x10, 3x9 etc. My front largest chain ring is a 42T. 

So, please point me in the right direction for a new front derailleur!! 

Thanks.


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## jlmuncie (Sep 10, 2010)

You







know the size, so next is a double or triple chain ring setup. Top or bottom pull is which way the cable gets to the derailleur, most Shimano FD's are dual pull so if you get a dual pull it'll work either way. Clamp location can make a difference depending on the frame you are putting it on. Top swing will have the clamp above the derailleur and bottom swing will have it below the derailleur. The pic is a top swing.


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## jeffj (Jan 13, 2004)

^ ^ ^ ^ ^ ^ ^ ^ The above pic is a bottom swing (high clamp). ^ ^ ^ ^ ^ ^ ^ ^ ^ ^

The pin they pivot from will be much wider on a top swing (low clamp) type.

*EDIT: jlmuncie has now posted a correct picture of a top swing front derailleur.*

It's kind of confusing, but if you mess with them enough, you find a way to remember which is which.

Some bikes can use either one, and some will require one or the other for various reasons. If in doubt, get one like your bike already has.

To confuse things even further (or give you more choices depending on how you view things) SRAM also makes some that are kind of a mid-clamp design. The good news is that either company's shifters work with any of them (unlike rear shifters).


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## jlmuncie (Sep 10, 2010)

Yep, I had a picture of each and posted the wrong one. I put in the right pic but now the image is too large, oh well.


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## rlouder (Jun 26, 2007)

I have an older top swing, bottom pull lx der. in my scrap box that looks almost new. 
I bought it cheap on ebay a couple years ago, thinking it was dual pull. 
Pm me if you want it - free.


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## hdparrish (Jan 24, 2008)

JensonUSA has been giving away (well, for $6) bottom-swing, top-pull, 34.9mm LX derailleurs for nearly a year now.

http://www.jensonusa.com/store/product/FD707A01-Shimano+Lx+M571+Front+Derailleur.aspx


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