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 Post subject: Why go longcage?
PostPosted: Sat Oct 27, 2012 7:18 pm 
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Joined: Sat Apr 28, 2012 9:33 pm
Posts: 28
Shimano Tech doc says, that a medium cage can take 34T in the back. Since this is the max (9s 970XTR) I dont understand why I should go longcage. I ride a standard XTR 970 44/32/22 setup. I have always used longcage RD, but a salesguy claims, that I can just use medium. Is he right?


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 Post subject: Re: Why go longcage?
PostPosted: Sat Oct 27, 2012 9:49 pm 
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Joined: Wed Jan 18, 2012 4:23 pm
Posts: 475
Location: Midlands, United Kingdom
You need to match the total capacity as well, check the tech docs.

(capacity=(largest front-smallest front)+(largest rear-smallest rear) so for a typical 42/32/22 with 11-34 you need a capacity of (42-22)+(34-11)=43

Rule of thumb (only) single chainring - short, double - medium and triple - long.

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 Post subject: Re: Why go longcage?
Posted: Sat Oct 27, 2012 9:49 pm 


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 Post subject: Re: Why go longcage?
PostPosted: Sat Oct 27, 2012 10:49 pm 
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Joined: Sat Apr 28, 2012 9:33 pm
Posts: 28
TheRookie wrote:
You need to match the total capacity as well, check the tech docs.

(capacity=(largest front-smallest front)+(largest rear-smallest rear) so for a typical 42/32/22 with 11-34 you need a capacity of (42-22)+(34-11)=43

Rule of thumb (only) single chainring - short, double - medium and triple - long.


:thumbup: :beerchug: Perfect explanation! None of the other guys I asked understood the Tech Doc correctly :noidea:


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 Post subject: Re: Why go longcage?
PostPosted: Sun Oct 28, 2012 2:11 am 
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Joined: Thu Mar 17, 2005 3:25 am
Posts: 2200
Location: Southern Indiana USA
I have a medium on a bike with an eccentric bottom bracket so I can optimize the chainstay effective length it has 22-32-44 front and 12-34 rear. Adjusting so that it barely makes the shift to big/big when in small/small the chain is rubbing on the chain on the top/forward roller of the rear derraileur so I never use small/small. It will not work very well at all since if you don't have an adjustable bottom bracket, you will likely have an even worse situation than I do. Getting enough chain to make the big/big will probably leave your chain rubbing in at least the small/small and small/2nd smallest and maybe up to 3rd smallest.

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 Post subject: Re: Why go longcage?
PostPosted: Sun Oct 28, 2012 6:47 am 
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Joined: Wed Jan 18, 2012 4:23 pm
Posts: 475
Location: Midlands, United Kingdom
No idea how you think having an EBB effects total chain growth from small/small to big/big.....however yes if you don't mind the chain being slackish in small/small (which you shouldn't really use anyway) then on some triples a medium is fine, I would've use it with the wider spacer Touring chainsets though!

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 Post subject: Re: Why go longcage?
PostPosted: Sun Oct 28, 2012 1:59 pm 
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Joined: Thu Mar 17, 2005 3:25 am
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Location: Southern Indiana USA
Simple, if you can't move the bottom bracket to get the chain on big/big you have to go in discrete increments of 2 inches since you can only add 2 links at a time. With eccentric bb on a non-single speed bike (Sir9 set up geared) you can cut the chain to a usable length and then rotate the BB to get it so that it will just shift onto big/big. At that point you have the minimum amount of extra chain when you are on small small. Without the eccentric BB you are liable to have up to 2 inches more chain when you are on small/small since you can't optimize the effective chainstay length on big/big.

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 Post subject: Re: Why go longcage?
PostPosted: Sun Oct 28, 2012 10:23 pm 
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Joined: Wed Jan 18, 2012 4:23 pm
Posts: 475
Location: Midlands, United Kingdom
A pair of links is 1" not 2" , 1/2" on wheelbase as it covers two runs of course.....

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 Post subject: Re: Why go longcage?
PostPosted: Sat Nov 03, 2012 3:22 am 
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Joined: Thu Oct 11, 2012 2:15 am
Posts: 66
exactly, total capacity is the key.

I use a middle cage xtr rear der. and 44-32-22 front... but i use 12-27 cassette (9speed), so middle is fine for this. 11-34 + triple; long cage is the best option.


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 Post subject: Re: Why go longcage?
Posted: Sat Nov 03, 2012 3:22 am 


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