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  1. #1
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    Rear Derailleur - Short/Medium/Long Cages - Please explain

    I'm new to the MTB world and would really appreciate an explanation. Could someone please explain to me what determines if I need a Short, Medium, or Long Cage rear derailleur? I'm guessing (and probably wrong haha) that the determining factor is if I'm running a 1x or 2x or 3x up front OR simply what my largest gear / my smallest gear is up front???? Please help explain!

    Thanks,
    Blake

  2. #2
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    Also, when going to sell my current rear derailleur, what can I measure to determine if I have a short, medium, or long cage?

  3. #3
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    If I was on a computer instead of my phone I'd include a link. In the drivetrain forum I believe there's a sticky regarding how to calculate.
    The length between the jockey wheels is what that refers to. A derailleur can only take up a predetermined amount of slack in your chain. If you shift to granny ring the derailleur has to be able to take up the slack in your chain in order to keep it tight enough to engage the teeth and drive the bike.

    Sent from my DROID RAZR using Tapatalk

  4. #4
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    When to use a Long Cage vs Short Cage Derailleur?
    X-9 10-speed rear derailleur on the SRAM website - they are listed as 55mm, 75mm, and 99mm for the short, medium, and long versions.

  5. #5
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    You're actually correct. It's determined by the difference between the largest and smallest ratios. You won't really ever run a short cage unless you run a road cassette. Once you see a medium and a long cage, it's pretty easy to see the difference. I've always ran two or single ring front setups with a medium cage in the rear.

  6. #6
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    Quote Originally Posted by kazlx View Post
    You're actually correct. It's determined by the difference between the largest and smallest ratios. You won't really ever run a short cage unless you run a road cassette. Once you see a medium and a long cage, it's pretty easy to see the difference. I've always ran two or single ring front setups with a medium cage in the rear.
    There's actually a formula. Because it's not just the largest to smallest ratio, but also the largest ring and largest cog and smallest ring and smallest cog difference.

    I run a short cage on my 1x9 drivetrain. The formula allows for this since I'm not running the large and small ring.
    Just get out and ride!

  7. #7
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    Thanks for all the replies guys! What I'm finding out is that there is A LOT that goes into switching from a 3x9 set-up to a 2x10 set-up. Another question I would have is do I have to get a different hub to accept the 10gear rather than my current 9gear? I have Crossmax SLR's if that matters.

  8. #8
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    I ride my bike instead of calculating formulas for cage length. You can run a medium cage on most setups and be fine. If you ride anything remotely techy, long cages are bad news.

    You don't need another hub for a 10 speed cassette. They are the same overall width as a 9. The cogs and chain are narrower. Going 2x10 isn't that involved. I would suggest a 1x10 with an 11-36 rear cassette. Start with a 30 or 32 front ring and go from there. It will suck at first with no granny, but you get used to it. I run a 1x9 with a 32 front and 11-34 cassette. A little extra gear would be nice on occasion, so I'll change when I go to a 10spd setup.

    Cassette
    Chain
    Appropriate shifter(s)
    Rear derailleur

  9. #9
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    as a general rule, short cages will work with a standard 1x setup, a medium cage with a 2x, and you will probably need a long cage for a 3x. probably.

    I have worked on some bikes that needed a long cage but the manufacturer (Specialized, in this case) that, when the derailleur was adjusted and you shifted it into the small-small combo, the chain would rub on itself on the derailleur, but if you shift it to the big-big combo, the derailleur would nearly rip itself off. it's best not to cross-chain your gears like this, but unless you never, ever, ever accidentally, maybe, cross-chain your bike, the bike should have a long-cage.

    the manufacturer should provide a maximum chain wrap number for each model, along with a maximum cog size, and you can figure out what you need based on the formula in the link above.

  10. #10
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    does this mean I could run a 10 speed 11-36 in back and swap out between a 28t and a 32t up front and would only need a short cage in the rear?
    What is the formula? or a link to the formula? Please.

  11. #11
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    So for your example, 11+28=39 and 36+32=68

    68-39 = 29

    So your derailleur needs a chain wrap capacity of 29. You could probably use a short cage SRAM X series derailleur, but you are on the edge of it's rated max capacity so if you set up chain length correctly and you end up having to remove a link on the trail for some reason (like fixing a snapped chain with a quick link) you could lose your largest cog in the back as a usable gear and risk breaking your derailleur if you shift into it accidentally before you replace your chain.

  12. #12
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    Re: Rear Derailleur - Short/Medium/Long Cages - Please explain

    Quote Originally Posted by 292beach View Post
    does this mean I could run a 10 speed 11-36 in back and swap out between a 28t and a 32t up front and would only need a short cage in the rear?
    What is the formula? or a link to the formula? Please.
    Yes, with 1x10 you can use a short cage.
    I have a 11-36 cassette and swap 28T, 30T and 32T based on the ride I am doing.

  13. #13
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    Quote Originally Posted by 292beach View Post
    What is the formula? or a link to the formula? Please.
    Did you even read the thread you just bumped?
    When to use a Long Cage vs Short Cage Derailleur?

    A short cage will work. You need 25T capacity for the rear and 4 for the front so 29T capacity. Most short have 30T capacity.

  14. #14
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    Quote Originally Posted by Slash5 View Post
    Did you even read the thread you just bumped?
    I guess I ride my bike instead of calculating formulas for cage length like kazlx. I was just looking for a second opinion. Sorry if I offended the forum POLICE.

  15. #15
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    Quote Originally Posted by Slash5 View Post
    Did you even read the thread you just bumped?
    When to use a Long Cage vs Short Cage Derailleur?

    A short cage will work. You need 25T capacity for the rear and 4 for the front so 29T capacity. Most short have 30T capacity.
    It's the lazy generation, don't want to research, just want answers handed to them.
    13 Lenz Lunchbox punkass

  16. #16
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    Quote Originally Posted by 292beach View Post
    I guess I ride my bike instead of calculating formulas for cage length like kazlx. I was just looking for a second opinion. Sorry if I offended the forum POLICE.
    might not want to bite the hand that feeds you, punk. people will remember that you're too lazy to read and learn something yourself and then you turn around and insult the people who are kind enough to help you more than you really need helped. I certainly will, and you can bet I won't be so kind as to give you a link straight to the information you need in the future.

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