When to use a Long Cage vs Short Cage Derailleur?

[Trentkc]

I have a new SRAM X9 long cage derailleur, and another X9 that I now realize is "not long". Both are brand new, but the short one is ~16mm shorter.

What is the proper application for long versus short cage derailleur? Will the short one work with a 11/34 cassette? Does it matter if the bike has a rear suspension or is a hardtail?

Is my shorter X9 a "short" cage or "medium" cage? Thanks //kct

[Speedub.Nate]

You've got a medium cage. Sram makes a short cage mountain derailleur in the X.0 line, but only goes as low as a medium in the X.9.

Quick answer: The medium cage will work, but you'll drop your chain if you accidentally shift to the small-small combo. Suspension *could* be a factor, depending on how much "chainstay growth" your frame experiences as your suspension cycles.

Long answer:

Derailleurs have a rated capacity. This is their ability to take up excess chain. After all, you need just about all of your chain to run in the big-big combo, whereas you have a bunch of extra links doing nothing when you run in your small-small combo.

Not that either of those cross-chain combos are normal to run in, but let me get to that in a minute.

Manufacturer stated derailleur capacities are as follows:
Shimano long = 45T; medium = 33T
SRAM long = 43T; medium = 37T; short = 30T

Speaking from experience, Shimano is a bit conservative in their capacity rating. I can only assume the same is true of SRAM (I'll get to that, too).

The easy capacity formula is to add your big ring & cog sizes, then subtract your small ring and cog sizes. It looks like this:

cap req'd (T) = (BIG ring - small ring) + (BIG cog - small cog)

...so for a typical 44-32-22 mountain crank & 11-34 cassette...

T = (44T - 22T) + (34T - 11T)
.. = (22T) + (23T)
.. = 45T

Using this simple forumla, you would need a derailleur with a 45T rated capacity to absorb all the possible extra links of a typical 27-speed drivetrain.

(I make the assumption SRAM stated capacity is conservative, since they list 43T as the long cage capacity -- 2T short of what is required by this forumla).

Where do shorter cage lengths come into play? Right here!

Even though the long cage will, in theory, take you down to the 22x11 gear combo and hold adequate chain tension, let's be logical: 22x11 is a combo you don't use!

Rather than use the generic formula, let's map out the capacity for each gear combination (based off of a Shimano cog pattern; SRAM will be slightly different):



44x34 starts off at zero because in that combo, all of the chain is being used up by the ring and cog, and the derailleur needs to take up none of it. As you shift through the cassette range (moving down the column), the amount of free chain increases as the cog size decreases.

Take a look at the useable gears, which I've outlined in green and yellow. Those fall near the stated capacity of the medium cage derailleurs. (I mentioned that Shimano's stated capacity is conservative, and in practice, I find their medium cage to be closer to 39T.)

For instance, in the middle ring (32) and the small cog (11), the table shows you've got to absorb 35T. This is near the stated capacity of either of the medium cage derailleurs. This gear combo remains useable, but you'd be better off shifting to your big ring for better chain tension.

You can also see that to use a SRAM short cage derailleur (30T capacity) on this drivetrain would leave you with two or three unusable gears while in the middle ring, and only about three useable gears from your granny ring. (Any number greater than 30T on the table would be near the limits of the short cage derailleur.)

Oops! Accidentally shifted into the unusable "red zone"? Nothing major: the derailleur cage folds back on itself, the chain droops, and you maybe drop the chain if you don't catch it in time.

In my opinion, it'd be stupid to size a chain any smaller than what is required to shift into big-big. If you accidentally force a shift into that combo, which is certainly possible when you're tired or "in the moment", you don't want to break anything. So chain length will be the same no matter what derailleur you choose.



Benefits of a shorter cage length?
- snappier shifts
- better chain tension
- less chain slap / greatly decreased drivetrain noise (!)
- better obstruction clearance / improved spoke clearance.
- slight weight loss -- but you gotta be a real weight weenie to appreciate this one.

[Call_me_Clyde]

This sticky thread is an edited version of a longer thread. It's intended use is as a quick reference guide for questions relating to derailleur cage length. If you want to read more, or participate in the original thread, it can be found here:

When to use a Long Cage vs Short Cage Derailleur?

Bob

[scrubs]

Great explanation, it's amazing how little of this can be found on the shimano website. So does that mean if I am running a triple front 22-32-44 on a BMC 4-stroke with 11-34 rear I need the longest cage?
Confusingly the shimano website doesn't list 'medium' & 'long' cage but uses the terms 'long' and 'super long', the latter rated as a 45T.

[ibismojo]

I have read all of the sticky as well as this post, and don't see any real talk about a 46T big ring. I am running a 46-34-24 with a normal xt rear cassette. I am thinking about changing over to sram drivetrain and thinking I need to get a long cage RD. I just want to make sure I am thinking right here.

[BikeLust]

I was just on the SRAM site and their tech manual states that the X0 rear derailleur has a capacity of 45T. The OP stated 43, 2 less than his formula where in fact the capacity matches same as Shimano. A minor point but worth updating on the sticky.

BL

[newmarketrog]

to properly run a sram x9 short cage rear der, which were still available through qbp this year, either a 32t ring with a 34 in the back or reverse combo will work fine. i've been running one for the last year with a 34t ring up front and a 30t in the back and there's room for more teeth. i really dig the short cage thang, less likely to snag on something.
rog

[DirtGash]

I'm running an X9 short cage rear with 36T front / 34T rear with no issues. I'm sure it's pushing the limits of what's doable, but it seems to be working fine althought many have said it won't.

Cool I think this just answered my question. I have a X-9 short cage, and am currently running a 32T front/ 32T rear, but am about to convert to a 1x9 MRP guide system. Am going to now run a 36T single front and am wondering if I can keep my 11-32 cassette or if I have to switch to a DH 11-26 which would suck as then I would loose all climbing ability.

But if you are running a 36T front and 11-34 cassette with no issues, I should be fine!

Gnarly!

[kapusta]

Cool I think this just answered my question. I have a X-9 short cage, and am currently running a 32T front/ 32T rear, but am about to convert to a 1x9 MRP guide system. Am going to now run a 36T single front and am wondering if I can keep my 11-32 cassette or if I have to switch to a DH 11-26 which would suck as then I would loose all climbing ability.

But if you are running a 36T front and 11-34 cassette with no issues, I should be fine!

Gnarly!

I'm confused about the last few posts. Are you guys both running single rings in the front? If so, the size of the ring is totally irrelevant as to the cage length. If not, saying "32t front, 32t rear" is useless information, as you need to know the size of the biggest AND smallest ring/cog in order to gain anything meaningful from the example.

The size of the rings and cassette cogs is meaningless. it is the DIFFERENCE between the biggest and smallest that matters.

So, dirtgash: You should be fine, the size of the front single ring is irrelevant. If a single 32t worked, so will a 36t, or a 38t or a 54t ring, or any other size ring you could possibly use.

[Zachariah]

Guys, why all the brainiac math? The OP just wants to know what cage to use with his 11-34 cassette.......fer cryin......

[kapusta]

Guys, why all the brainiac math? The OP just wants to know what cage to use with his 11-34 cassette.......fer cryin......

Read the responses and you'll understand why there is not a simple answer to the question when you don't say A) what you are running up front and B) if you are willing to loose the use of the small/small combo.

[MTBgreatfalls]

This is great stuff, I was wondering about switching to a medium or short cage. now I have something to go by.

[IRONMAN1518]

Soooooo.....................I think I've understood most of this......I think?
If I a using an 11-34 cassette and a 22-44 crank, I can use a short cage xtr rear der as long as I don't "crossshift" out of the "Green Area" in the above chart, correct?
I'm in that decision @ this time which der to run. Thanks for any further input. I have a short cage der comming and thinki I need to buy the SGS cages and replace the SG cages,?? I am right or waaay of, please?
Thanks!!

[Prophet Julio]

I set up my chain big big +2 and can use all the green and the purple where there is very little slack. The yellow is marginal.

I lost a couple of long cages to sticks and rocks, so I switched. What I found was crisper shifting with the short cage, less chain slap and much better clearance.

I would never go back. Makes you a better (more conscientious) shifter.

So on the small cog you get slack when you use the smaller rings. In the middle cog you get some slack on the smallest ring. Big deal. That is the only downside.

[chomxxo]

I use a short cage X.0 with 11-34t cassette and 29-42t 2x9 up front. No shifting problems to speak of and I can hit all gears. I run the chain pretty tight.

[adiokyro]

i have always run 11-34/long cage/xt triggers and because of mainly this thread i set my new rize up with pg990 11-32, X-0 medium cage, and X-0 twisters--i really really love this set up, ive never ridden anything with such nice crisp and quick shifting! i love that i can dump all 9 in a single twist--really love it

[russelr]

too much to quote

that was the best answer i have ever read on mtbr. just wanted to let you know i saved it to a word document for a future reference.

[Thrasher]

i have always run 11-34/long cage/xt triggers and because of mainly this thread i set my new rize up with pg990 11-32, X-0 medium cage, and X-0 twisters--i really really love this set up, ive never ridden anything with such nice crisp and quick shifting! i love that i can dump all 9 in a single twist--really love it

I was reading all of the extreme details above and not sure about all the math stuff.
The info is quite detailed and informative but I'm just looking for a 'quick fix' answer to get my bike back on the trail with quicker shifting and a low profile. I believe I'll be able to run a medium cage on my setup? Right? My setup is 3 rings (not sure of the count on sprockets) up front and the 11-34 9 speed cassette in the back. I'd rather go with the medium cage Derailleur since I ride lots of rough/rocky/rooty areas. I also do downhill so the medium would probably be better for that. I don't care if I have the chain slack that Prophet Julio mentioned since I don't use that gearing much. I'm thinking this should workout. I'm going to go with this one. http://cgi.ebay.com/NEW-SHIMANO-DEOR...d=p3286.c0.m14

My main concern is I want to have great climbing gear ability with the small front and big in back since I also do lots of front range climbing. BTW, this is going on my 2005 Kona Dawg Dee-Lux that's taken one hell of a beating and deserves a new Derailleur .

[adiokyro]

i think u shud be fine with that--i had that shadow der too n it is pretty lo-pro. u just cant ever be in ur big/big or small/small but who does that anyway--like my 11-32 tho n seems fine even for steep climbs

[Thrasher]

i think u shud be fine with that--i had that shadow der too n it is pretty lo-pro. u just cant ever be in ur big/big or small/small but who does that anyway--like my 11-32 tho n seems fine even for steep climbs

Cool, thanks for the info. I can't recall anytime I'd be using those gears either so time 2 purchase!

[oheckler]

Has anyone tried using a really short derailleur? I am currently running a 1x8 setup on my steel Ibis Mojo with an older XT long cage rear derailleur. I am planning on switching to an older short cage xtr derailleur but have considered using an older Dura Ace RD-7402 rear derailleur for really crisp shifting. Does anyone know if this derailleur will clear a 32 tooth cog?

[nony]

Just curious, does a longer cage keep the chain more taut, lessening a dropped chain?

[bhc]

Has anyone tried using a really short derailleur? I am currently running a 1x8 setup on my steel Ibis Mojo with an older XT long cage rear derailleur. I am planning on switching to an older short cage xtr derailleur but have considered using an older Dura Ace RD-7402 rear derailleur for really crisp shifting. Does anyone know if this derailleur will clear a 32 tooth cog?

I have run an old Dura Ace on a 1 x 6 set up with a 32 in back. Shifted fine. But I don't know what model # it is.

[bgfthntr]

I use a XT Short Cage with a 22-32-44, 11-34 combo and no problems. When checking chain length I made sure I could shift in 44-34T combo (i don't use it) just in case I shift there by accident. The last derailleur was the recent SLX Shadow derailleur that got nailed by a rock and took the the hanger with it.

[bde1024]

I was wondering if a X.O shortcage would work with an 11-34 cassette and 44-29 or 42-29 rings? Anyone have any experience with that sort of setup?