[TomMcT]

Hi, all,
I am going to build up a new 12 spd bike, and will be using the current XT 10/45T cassette.
I saw (somewhere) that the Shimano 12 spd rear derailleur is also 11 spd compatible, and was hoping that this might imply that an 11 spd Shimano RD would be 12 spd compatible. Does anyone know if it would work? I have no way to test this myself.

My motivation to do this is:
I want to run a GS cage RD instead of an SGS, to minimize rock damage. 12 spd XTR RD GS cage is easy to get but expensive, and that is my fallback option. 12 spd XT RD GS cage is a defined Shimano part, and is my preferred option, but have no idea when I could get one. So, if I could make an 11 spd XT RD GS cage work, I would get one....

Thanks in advance.

 

[Hawthorn]

I did it the other way round, I used a 12spd slx on my 10spd 11/46 cassette, shifters and derailleurs are compatible but shifting performance would suffer on a 45t with a short cage xtr 11spd, get a 12spd medium cage derailleur and be done with it

 

[AKamp]

I am running last gen xtr (gs?) on 12sp 10-45. No issues at all. Get appropriate shifter though. Doubt it would work on a 51

 

[tstinchy]

Yes it is. I'm doing that exact same thing;12 speed casette (10-45 tooth, short ratio), 12 speed shifter (deore, that's all that was available, get the xt if you can for the 2x upshift) and older xt 11 speed derailleur. I think the system will shift a little smoother with the 12 speed specific derailleur, but it's still pretty good with the 11 speed. One note, you will need a 12 speed specific chainring too, as the new HG+ chains don't work with 11 speed chainrings.

 

[chucko58]

I'm using a 12 speed XT rear derailleur with an 11 speed XT shifter and Deore 11 speed 11-51t cassette. Works fine, as long as the derailleur hanger is straight. I mention the hanger because this is a recurring problem on my bike, a 2007 Chumba XCL.

 

[AKamp]

I am not sold in needing a 12spd chainring. I have an old 985 race crankset with a wolf tooth chainring on it. The chainring is probably 4 years old and makes no noise, doesn’t drop chains. Smooth as silk. Maybe there is enough wear on the chainring it doesn’t matter. Probably not perfect but runs just as smooth a my 12spd full groups.

 

[TomMcT]

Thanks, everyone, that is a big help! I will probably go with the 11 spd derailleur. Will definitely use the `12 spd cassette, chainrings, and chain, and I already have them on hand.

 

[J_Westy]

According to this chart, the derailleur ratio is the same at 1.1, so they should be interchangeable.

Wide-range cassette chart

Cassette and Drivetrain Chart https://docs.google.com/spreadsheets/d/16C3Rz6qmzmurSNd-L3IeMSFukkBFV6D1DRbfS59EDrE/ Thought some folks might find this useful. Every cassette I can find that's wide range and most that aren't. Various cranks and calculators also included. There's some fudge...

www.mtbr.com

 

[macduff]

I'm using an 11spd XTR RD on a 12spd 9-52 cassette (XD hub) its probably at its max capacity at that gearing range & its on a hard tail so I dont have to accommodate any chain tension changes from suspension movement, all it took (swapped from 10-50 cassette) was a tweak of adjusters . I was using it on a HD3 with a 10-50 cassette previously with no issues, prior to moving it to my Hardtail.

 

[crustin]

I have the XTR 12 speed gs now with the 45t cassette. It's awesome, but having a fancy derailleur makes me nervous. I only have it because I lucked out and got it from some weirdo on facebook for $100. I also couldn't find one of the fabled m8100 gs derailleurs, so I was looking into the m8000 option until those become available. If it works great, I'll sell my XTR. Will report back here.