Rear Derailleur Cage Length?

Postby Greyway on Mon 5/Nov/12 1:05pm

I am running 3x10 (11x36) with a Sram x9 rear derailleur. When I look at websites, they say I should have a long cage (99mm). Yet the one I am running is medium? 75mm centre to centre. Am I measuring it right?
I can only see disadvantages in a long cage,i.e. weaker and heavier. Or would I get better shifting with a longer cage?
Greyway
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Re: Rear Derailleur Cage Length?

Postby Dr. Fuentes on Mon 5/Nov/12 1:30pm

google it.
Dr. Fuentes
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Re: Rear Derailleur Cage Length?

Postby NickCW on Mon 5/Nov/12 2:12pm

The derailleur is probably way out of its capacity, this may cause an assplosion
NickCW
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Re: Rear Derailleur Cage Length?

Postby sifter on Mon 5/Nov/12 2:44pm

NickCW wrote:The derailleur is probably way out of its capacity, this may cause an assplosion


:withstupid: I gather the issue is cross-chaining in the big-big. Maybe also needed for chain-tension in small-small? I'm just making this up...
sifter
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Re: Rear Derailleur Cage Length?

Postby Conners on Mon 5/Nov/12 3:01pm

Greyway wrote:I am running 3x10 (11x36) with a Sram x9 rear derailleur. When I look at websites, they say I should have a long cage (99mm). Yet the one I am running is medium? 75mm centre to centre. Am I measuring it right?
I can only see disadvantages in a long cage,i.e. weaker and heavier. Or would I get better shifting with a longer cage?

Oh yeah, those side plates are gunna weigh a tonne at a whopping 24mm longer.

I'd say if you're not a mong who rides cross chained, you'll probably be sweet. Until you have a brain fade moment and cause the above mentioned assplosion. Then you'll be well fooked, and needing to temporarily singlespeed your boik to get home.
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Re: Rear Derailleur Cage Length?

Postby danose on Mon 5/Nov/12 3:04pm

just ditch the big ring (and up size the middle) and you'll be good (big rings are for racing whippets only - 36x11 is more than tall enough for everything else)
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Re: Rear Derailleur Cage Length?

Postby Greyway on Mon 5/Nov/12 3:36pm

Conners wrote:
Greyway wrote:I am running 3x10 (11x36) with a Sram x9 rear derailleur. When I look at websites, they say I should have a long cage (99mm). Yet the one I am running is medium? 75mm centre to centre. Am I measuring it right?
I can only see disadvantages in a long cage,i.e. weaker and heavier. Or would I get better shifting with a longer cage?

Oh yeah, those side plates are gunna weigh a tonne at a whopping 24mm longer.

I'd say if you're not a mong who rides cross chained, you'll probably be sweet. Until you have a brain fade moment and cause the above mentioned assplosion. Then you'll be well fooked, and needing to temporarily singlespeed your boik to get home.

Definitely dont want to be a "fooked mong on a boik" :blink:
Thanks for answer guys, can see now how I could have had an assplosion.
Interestingly my Epic was sold from bike shop with medium cage ( 2x10 changed to a 3x10 ), cause I am an old f@rt that rides a lot of steep hills (do rides like in Dave Mitchells book), so needed a super low granny, but agree, dont use the big chainring a lot....though it was handy in the race I did yesterday.
Greyway
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Re: Rear Derailleur Cage Length?

Postby Simonius_Titius on Mon 5/Nov/12 3:43pm

If you don't have a real problem with the long cage you might as well leave it on. A shorter cage will normally shift a bit crisper but nice new idlers will do that too. Measure length between the pulley centres.

Try not to have a setup where trying to get into big-big during the heat of battle on a blue moon will wreck your chain, kill your derailler, shove it past where your dork disk should be, then onwards to kink your spooks and rip your nipples through the rim.
None of which will concern you unless you regain consciousness.

If the aforesaid is acceptable or even attractive to you, try to keep it for the biggest rear cog only. I'd start by setting the chain length to be nasty tight but just doable on big-big then seeing whether chain bounce is acceptable in small-small, considering that you don't go very fast in small ring.
But first, check whether your derailleur is perfectly lubed - the top pivot in oldies often gets dry because it is not as easy to strip and reassemble as the other bits.
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Re: Rear Derailleur Cage Length?

Postby danose on Mon 5/Nov/12 3:53pm

Greyway wrote:Thanks for answer guys, can see now how I could have had an assplosion.


as long as the chain is actually correctly size for big/big (and checked for right length at full sus compression) it won't assplode - you will just end up with slack chain in the granny/small combos (again a combo you shouldn't really be in).

wifes meta4 came stock with 3 rings and a sram med cage so technical 'over capacity' (only an 11-32 cass though) - I only noticed the issue when I went to switch 11-32 for an 11-34 and couldn't get chain tension right (again fix was to ditch the big ring)
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