[Closed] Running a 12-36 cassette with a Short caged rear mech.

11-34 gives a wider range, weighs less and won't incur mech issues. I'd return the 12-36.

I would benefit from the 36 over the 11.
What Mech issues?

Yep, the only point of 12-36 is either to bodge an 11-36 cassette, or deal with too-high front rings. Instead of going up to 36, it's better to go down at the front.

But to answer the actual question, it's an It Depends- Shimano shortcage is very short, it'll be long enough for some frames but if you've got a chaingrowthy design, maybe not.

(I didn't know there's a shortcage XT)

Does "short cage" XT Mech even exist?

Shimano's "short" cage XT is a medium by anyone's standards.

Either way, Zee/Saint/SRAM short cages have no issues with 11-36 so can't see an issue with 12-36

honourablegeorge - Member

Either way, Zee/Saint/SRAM short cages have no issues with 11-36

They do- not compatible with all frames, they can't take up the slack of some designs with lots of chainlength change. Does seem rare though.

I didn't know there's a shortcage XT

Does "short cage" XT Mech even exist?

Yup, On closer inspection I currently run what appears to be a Medium caged.

So let me ask a new question,

Will my Medium caged rear mech have an issue running a 12-36t cassette???

it's better to go down at the front.

I've been told otherwise, Wouldn't dropping to a 30t from 32t be minimal difference?

Sounds like a job for the [url= http://sheldonbrown.com/gears/ ]Sheldon Brown gear calculator[/url]!

My medium cage XT is working fine with a 40t T-Rex so you'll be ok.

If the XT mech is a Shadow model they are designed to run with a largest sprocket of up to 36T so you will be absolutely fine.

I've been told otherwise, Wouldn't dropping to a 30t from 32t be minimal difference?

32/36 is near as dammit the same as 30/34.

FWIW, 36/32 gives the same gain ratio (1.7) as 34/30. 12/32 gives a slightly lower gain ratio than 11/30. So with 11-34 and a 30t you actually have a wider spread of gears than 12-36 and a 32t.

Where can I get a Dummies guide to bicycle gear ratio's

Confusion!

Sounds like a job for the [url=sheldonbrown.com/gears/]Sheldon Brown gear calculator[/url]!

I'm not sure but here are some pointers
my understanding is that "capacity" is the issue - the ability for the rear mech to take up slack
the late great Sheldon Brown defines it here

[url] http://sheldonbrown.com/gloss_ca-g.html [/url]

but as single front ring capacity is 36-12 = 24

Shimano includes capacity on their tech sheets - not sure what XT mech talking about but suspect its the GS (shortish?)one here or find shimano number on your mech and google it with shimano tech sheet

[url] http://techdocs.shimano.com/media/techdocs/content/cycle/SI/RD/SI_5W70A_005/SI_5W70A_005_En_v1_m56577569830655487.pdf [/url]

which has a capacity of 33 so no problem with 36-12 other than the spec lists max rear cassette as 34 - this is where trial and error play and messing with the b screw - answer I suspect is probably yes as spec sheet wasn't really written with single front perspective - hopefully someone has run it and will come along - beware people who have got away with it on ten speed - they were designed for 36t - running above 32 with 9 speed is pushing it in my opinion

running above 32 with 9 speed is pushing it in my opinion

Rubbish, non-Shadow mechs were designed for a 34t, Shadow mechs were designed to work on 36.

GS will be fine, SS would perhaps have been pushing it, but as said, they don't do an XT SS mech.

[I]running above 32 with 9 speed is pushing it in my opinion[/I]

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The Shimano tech manual states that a 9 speed Shadow XT mech is designed to work up to a 36T.

Yup, there's some contradiction as Shimano used to claim 36 tooth wouldn't work with their 9-speed mechs, and you had to upgrade to 10 speed for that. Then they decided to make a 36 tooth 9-speed and suddenly the guidance changed 😉

there's some contradiction as Shimano used to claim 36 tooth wouldn't work with their 9-speed mechs

So why do they make a 9sp 12-36 cassette then? 😉

I looked into exactly this question recent when building a touring bike for Mrs PP. We want LOW gears and a 22/34 bottom gear was always fine on her 26in bike, but I bought her a 700c bike, so a rethink was needed. No way was I going 10sp for touring, but Shimano make a 12-36 cassette which was originally intended for 29er MTBs
Fine
But a normal Deore M591 mech will only take a maximum 34t sprocket, so I had to change the mech to an M592 to solve that.
I don't think they make asp XT mechs any more, certainly I couldn't find anything better in stock at Madison (I work in a bike shop, I can see what's available) although it's possible there may be old stock lying around

PeterPoddy - Member

So why do they make a 9sp 12-36 cassette then?

That was kinda the point, everything up until that came out said "can't be done, max 34T, you need 10 speed" then they decided to sell a 36T and suddenly it was all good. Cheeky beggars that they are

I have a XT M771 which is a none Shadow mech and looking at [url= http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Deore-XT/SI_5W60A_002/SI_5W60A_002_En_v1_m56577569830648262.pdf ]this[/url], It'd seem I'd be pushing my luck,

Thoughts on weather I should push my luck and try it? 😕

I don't think they make asp XT mechs any more, certainly I couldn't find anything better in stock at Madison (I work in a bike shop, I can see what's available) although it's possible there may be old stock lying around

You didn't look very hard then, RDM771GS and SGS both have good stock at Madison, found in one search! Hopefully you'd look a little harder if you were checking for a customer 😉

Tried to change my order from 12-36t to 11-34t but it was too late,
Question is should I just send it back or should I give it a go?

You didn't look very hard then, RDM771GS and SGS both have good stock at Madison, found in one search! Hopefully you'd look a little harder if you were checking for a customer

Fair enough, no I didn't look that hard to be fair. I wanted Deore anyway. 🙂

So thoughts on running a 12-36t on a non shadow M771 mech that officially clonks out at a 34t?

Should I send it back for a 11-34t or is there a viable chance it'll work, maybe with longer B-tension screw?

I think you'll be fine but the only way to find out is to try it.
I run 12-36 with a Saint 810 short cage mech no problems.
The Shimano tech docs showing max size sprockets are a bit of a puzzle and probably err on the side of caution.I have run bigger sprockets on both 8 and 9 speeds no problem.I am also sure I have seen new(road) bikes specced with sprockets bigger than the tech docs guidance too.

shimano are often vastly conservative on their max/min limits - I've run a road rear mech with a supposed 11-28 max cassette size limit, with a 11-34 no problem!

The Shimano tech docs showing max size sprockets are a bit of a puzzle and probably err on the side of caution

shimano are often vastly conservative on their max/min limits

Sounds promising, Think I'll give it a go.