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PostPosted: Tue Oct 29, 2013 9:34 pm 
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Location: Canada
I searched and it does not seem to be clear.

I need that rear derailleur, and I am running either :

11-36 cassette with 39-26 rings
or
11-36 cassette with 38-26 rings

Do I pick the medium cage or long cage?

thanks guys


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PostPosted: Tue Oct 29, 2013 10:16 pm 
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Location: Aarhus, Denmark
Short for single chainring, medium for double and long for triple. At least what i've been told. A Long-cage can be run with a double setup though.

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Posted: Tue Oct 29, 2013 10:16 pm 
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PostPosted: Wed Oct 30, 2013 7:28 am 
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A long-cage worked perfectly with my 2x10, but was not good with 1x10 setup. I would take a medium cage for 2x10 setup.


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PostPosted: Wed Oct 30, 2013 12:21 pm 
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Location: Sofia, Bulgaria
The difference between the cage lengths is the capacity of the deraileur to manage chain slack. The capacity is expressed in teeth and from shimano's website the medium cage one has capacity of 35T and the long cage one has 41T.

How to calculate the needed capacity - it is the difference between the largest chainring minus the smallest chainring, plus the difference between the largest cog minus the smallest cog. So for 39/26 and 11/36 it is: 39-26 + 36 - 11 = 38T capacity required.

Even if you use shorter cage than required, nothing wrong will happed, as long as you do not shift into the small/small chainring/cog combination. And even if you switch to the small/small combination the pulleys will hit the chain and the chain will be very slack, but nothing should brake.

So I say - go with the medium cage one, you will be ok.

Hope this helps,
Stefan


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PostPosted: Wed Oct 30, 2013 12:23 pm 
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thanks guys!!

now I only need to decide if I wait, and risk going with the 987 XTR brakes or go with the proven design of the 985 brakes


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PostPosted: Wed Oct 30, 2013 2:19 pm 
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As far as I know, Shimano makes two XTR Shadow Plus derailleurs -- a long cage (GS) and a "super" long cage (SGS.) I'm pretty sure they recommend the SGS for the 38/26 11-36 "trail" setup. Though my memory may be a little foggy, I did this research last year when making the same purchase and I ended up with the SGS. It works perfectly. Not sure what kind of bike you're putting this on but it's important to consider suspension movement and chain growth. Some dual suspension bikes require pretty long chains so the SGS is even more important. The SGS derailleur is not weird looking in any way (despite the Super! name...) I'm not sure I've ever seen a bike with the shorter SG Shadow Plus -- so that's saying something.... I think the SGS is the "normal" one.

Here's a good thread with people pondering the same question:

http://forums.mtbr.com/drivetrain-shift ... ost2911476" onclick="window.open(this.href);return false;


Last edited by planB on Wed Oct 30, 2013 6:30 pm, edited 1 time in total.

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PostPosted: Wed Oct 30, 2013 5:06 pm 
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thanks for this link, the pictures on page 6 absolutely prove the need for a SGS with a 2x10 setup like mine.


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PostPosted: Wed Oct 30, 2013 8:30 pm 
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As already mentioned, Shimano doesn't do short, medium and long cages.

I was running the XTR derailleur with the shortest cage on my old bike, with 2 x 9 (38/26 and 11-34). I am quite sure my current bike has the short version too (the latest version with Shadow Plus), and I am running 38/24 with an 11-36 cassette. No problems whatsoever :)

Here's some more info that I found very useful (is it OK to post this link?): http://forums.mtbr.com/drivetrain-shift ... 05890.html" onclick="window.open(this.href);return false;

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PostPosted: Wed Oct 30, 2013 9:07 pm 
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Location: Sunny UK
a medium can be run with double providing you don't use the smallest chain ring with te 3 or 4 smallest sprockets at the back .... best avoided if possible.


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PostPosted: Wed Oct 30, 2013 10:22 pm 
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Given my bike is a hardtail, maybe the shimano GS would be fine?


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PostPosted: Wed Oct 30, 2013 10:25 pm 
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As far as I know the Shimano "short" cage is a bit longer than a SRAM medium cage. Please correct me if I'm wrong.

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PostPosted: Thu Oct 31, 2013 10:30 pm 
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the link to mtbr has me confused, the guy showing picture has a full suspension bike.

So, will a shimano GS be fine with my gear ratio on my hartail?


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PostPosted: Fri Nov 01, 2013 4:55 am 
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Yeah, the GS will be fine. I've always ran the GS on my full suspension with no issues.


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PostPosted: Fri Nov 01, 2013 10:16 am 
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I am actually not 100 % sure my cage is the shorter GS one. According to Shimano, the capacities are 35T (GS) and 41T (SGS) (source: http://cycle.shimano-eu.com/publish/con ... RD-M980-GS)

According to a thread here on WW, the difference in cage length is 11 mm (source: viewtopic.php?f=1&t=107966). I can measure the cage length of my RD when I get home.

It looks like Specialized are speccing double chainring hardtails with the XTR GS RD (source: http://www.specialized.com/dk/en/bikes/ ... r-29#specs).

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PostPosted: Fri Nov 01, 2013 11:23 am 
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It'll say (somewhere) on the mech or cage. And FWIW, those capacity specs (35/41T) are very very pessimistic. I've run an old XTR short cage on a triple without any issues, and currently running a medium (GS) on a triple/FS.

It's usually more down to setting it up properly and being *roughly* within the capacity. Worst case (if it's set up properly) is you'll not be able to use a couple of gears, and they are gears that you really wouldn't want or need to run anyway as they are duplicated elsewhere. (small chainring and small sprockets)

http://www.gear-calculator.com/#
Will help.


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Posted: Fri Nov 01, 2013 11:23 am 
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