XTR M952 Short Cage - Maximum Rear tooth capacity

[Retrorockit]

Another option would have been an 11-28 cassette.

 

[bold stelvis]

Again, just to avoid confusion

Max sprocket size != capacity
they are two different things. Cage length mostly affects max capacity only (ie the ability to manage chain tension over the entire range)
max sprocket size is mainly down to how far out you can manage to get the derailleur guide jockey wheel to sit so it doesn't collide with the largest sprocket - cage size doesn't really matter.

 

[Retrorockit]

Again, just to avoid confusion

Max sprocket size != capacity
they are two different things. Cage length mostly affects max capacity only (ie the ability to manage chain tension over the entire range)
max sprocket size is mainly down to how far out you can manage to get the derailleur guide jockey wheel to sit so it doesn't collide with the largest sprocket - cage size doesn't really matter.

Cage size usually doesn't matter. But with some newer derailleurs being able to run up to 11-51t cassettes (40t range) some short cage SS can't handle that any more. 11-40t =29t range and that's about the limit for SS cage derailleurs. The common MTB GS mid cage is probably OK for 1x drivelines. I avoid SGS cage derailleurs if possible for 26" bikes due to it being very close to ground level in the mid gears.
There are derailleur hanger extensions that allow older derailleurs to run with larger cassettes. Then cage length (total capacity) becomes the determining factor.
Derailleur factoid. ( factoid= I haven't tried all possible combination myself) The 10/11 speed Shimano SLX clutch type derailleur landed almost on top of the SRAM 1:1 cable ratio (SRAM1:1.11, vs 1:1.13 Shimano). I have tested this by using a SRAM NX gripshifter with SLX 11 speed on 1x11. The 1x conversion lets me run a Front Freewheel setup ( seriously retro concept) on my vintage XC bike. The retro factiod is that this derailleur should work with SRAM 8/9 speed gripshifters including the very retro 1/2 pipe versions. The Zee M640 is an SS cage version of the SLX clutch derailleur for DH (28t), and FR (36t). The hanger is the only different part# according to Shimano's exploded drawing. No plastic bits to break off. The FR version hanger is also the same part# # as the SLX hanger. Just be aware that my testing was done with Jagwire Elite Link solid metal cable housings for maximum shift accuracy. These are retro, and great for bringing mechanical disc brakes up to modern standards, but it's a very pricey cable kit. If you have slack cable housings flapping around inside the frame or crappy old cables this may not work.

 

[integerspin]

Put a photo from the side of the mech with the mech over the big sprocket.

 

[Retrorockit]

I'll get a photo up tomorrow.
Here's a page on the XTR RD-M950

Shimano Rear Derailleur Specifications - the Buyer's Guide, 2015

Bicycle rear derailleurs Shimano features and comparison, bikepro.com

www.bikepro.com

You'll notice that the GS has 33t total capacity 22t front difference, and 11-32t cassette so in 2x MTB it would be 12 t difference in front with 21t in the rear
In a 1x situation an 11-40t cassette is within spec as far as total capacity goes.
The SGS has the same 22t front and rear 21t limits listed, but 38t total capacity.
My XTR is an M960 GS, It shows the same 33t GS capacity, but 43t for the SGS long cage. It is rated by Shimano for 34t max. cassette. IDK if it's actually any different or they just released a bigger cassette than they offered before.

 

[Betsy]

Cage size usually doesn't matter.

The issue for me (previous pg) was having sized the chain using the largest cog to largest chainring method (34t to 49t) the GS cage with it's 67mm centers wasn't long enough to offer enough tension to the chain for the smaller cogs while using the smaller chainrings but the longer SGS cage with it's 87mm centers gave a longer distance for the chain to travel which removed the slack.

 

[Retrorockit]

Doing the math front capacity is 46-26=20t which is in spec. for GS and SGS. The rear 11-34 capacity is 23t which ijust over spec. but by about the 2t left over form the front. But the total is 20t+23T=43t. This is a bit beyond even the SGS m950 series 38t listed capacity. Out of reach for the GS 33t total capacity. Going to 49t-27t puts you at 22t front capacity which is in spec, but adds 2t to total capacity for 45t.
The M960 SGS shows 43t total capacity and would be in spec with your 1st setup. But just over with your 2nd one. Some people say hardtails can go over a bit more than suspension bike because of chain length changes as the suspension moves that Shimano might be allowing for.
Be aware that my examples (M950/960) are Rapid Rise low normal derailleur. M951, m961 woulld be the normal actuation versions. I'm not sure what M952 signifies vs. M951? Maybe it's a Mega range version??

 

[Betsy]

Boom! .. mind blown

It works, so shudd'up you! don't jinx it

The only minor issue which it currently has is lifting the chain from the 36t middle ring onto the 49t large ring (i know these chainring sizes are not ideal but they were the only NOS Pace rings i could find)

The (friction) shift from middle to large works perfectly while the bike is on the bike stand but it's a struggle to lift the chain onto the 49t ring while force is being applied through the crank / while pedaling..

I've tried cable tension..

Raising the mech and/or overcompensating with the limit screws.. ie- push it too far over to get it to engage and then pull it back in line but this can drop the chain onto the crank.

Toeing the mech in or out.. nope.. the only fix i've found is to stop pedaling before i shift and push the front mech over onto the big ring momentarily before i start pedaling again (an idea i got while reading the 'Rivendell float shifting method' ) this does the trick but i need to get my brain in gear because i never remember to do it till it's too late.. do you have any other suggestions?

 

[Retrorockit]

I've run 48-32-28. The shift from 48-32 was slow but always worked. But that was before I converted it to an Ebike 1x8. I wasn't doing anything with large cassettes back then. LX M580 Mega 9 is what I had. Are you using trigger shifters or grips? Maybe a gripshifter willl let you feel it into gear?
I went to grips and Rapid Rise a long time ago, and still use them.
FD are all low normal BTW.
There are some diffferences between 44t MTB FD, and 48t Touring FD. The radius around the big cog is different. Coming from 46t to 49t you could have either one? 48t radius is uncommon in XT or XTR, but more easily found in LX, or Nexave series. If Pace is the Biopace oval chainring that could complicate this.

 

[Betsy]

I've run 48-32-28. The shift from 48-32 was slow but always worked. But that was before I converted it to an Ebike 1x8. I wasn't doing anything with large cassettes back then. LX M580 Mega 9 is what I had. Are you using trigger shifters or grips? Maybe a gripshifter willl let you feel it into gear?
I went to grips and Rapid Rise a long time ago, and still use them.
FD are all low normal BTW.

It's a bit of a mismatch.. Dura-Ace 9sp thumb shifters (indexed at the rear, friction at the front) M952 front/rear and Pace triple rings.. annoying as hell that every gear works like clockwork on the bike stand but struggles to lift from 36 to 49 in practice