Compatability - Deore XT 11sp M8000, 10sp T8000, running a clutch derailleur on a triple..

[wafter]

Looking for a bit of advice please!

I like triples and hydro brakes so am looking at the 10sp Deore XT T8000 "Trekking" groupset, which centres around Shimano's last (and I think now discontinued) high-end triple crankset (48/36/26).

This appears to be an offshoot of the 11sp M8000 mtb groupset and many components are similar, so I think things should be broadly compatable.

There are a couple things I'd like to try but I'm not 100% sure would work...


Use with an 11sp cassette and chain with M8000 shifters

The T8000 shifters are 10sp while the very similar M8000 shifters are 11sp. I assume that all being MTB-derived the derailleur actuation ratios (cable pull : derailleur movement) should be the same, so can I use M8000 shifters to control the T8000 FD and (an as yet indeterminate - please see below) RD to run an 11sp chain and cassette?

I'm aware that this would involve running the 10sp crankset with an 11sp chain, although from what I've read it seems that many are doing this... but would welcome any thoughts on this too


Use of a clutched rear derailleur with the triple setup

The T8000 RD has a long SGS cage giving 47T capacity, 22T max front difference and 32-36T low sprocket on the cassette - but unfortunately does't have a clutch (which I'd value very much given where I ride).

The M8000 RD with SGS cage also gives 47T capacity but only 18T max front difference (the M8000 triple is 40/30/22 IIRC) and 40T low sprocket on the cassette - this model does have a clutch.

Can anyone suggest whether I might get away with using the RD-M8000 with the triple, or whether I'm likely to be able to lash up some hybrid abomination by swapping bits like cages around please?

Also, can anyone shed any light on what factors determine the amont of chainring difference / range an RD can handle, since the two above have the same capacity? Also, what determines the ideal low sprocket on the cassette - perhaps the distance the top jocket wheel sits below the cassettes, so something that could possibly be manipulated by swapping the RD mount that bolts to the hanger..?


I'm aware that some are fitting MTB cages to GRX 810 RDs to get more capacity, but obviously I can't run this RD as it's road-based so has a different actuation ratio to the MTB stuff.


Cheers!

 

[wafter]

On the offchance anyone has similar questions, many more hours spent scouring the internet suggest that:

There are questions over the compatability of 10/11sp MTB drivetrains as apparently (according to Bike Gremlin) 10sp ("Dyna-sys") has a slightly lower derailleur ratio and higher cable pull ratio than the later 11sp "Dyna-sys II) offerings; suggesting that a system would have to 100% one or the other to work correctly. Conversely however, Shimano list some of their RDs as both 10 and 11sp compatable..


Also, I've read that the "max front difference" expressed for RDs is just a function of their total capacity and the range of the cassette they're expected to be used with - ostensibly they're described this way to make it easier for consumers to understand... but also seems to muddy the waters..

 

[bikeworkshop]

I think you'd best avoid it - here's my take:

Clutched derailleur was really to improve chain retention with a single front ring, and although it does have some benefit on a double, it's often a bit nasty.

i would think the extra brake on cage rotation might throw the chain off on a downshift to the small ring, or cause skating either way.

There is also some very complex shaping to the rear derailleur, which changes alignment as the cage rotates - I assume this is to deal with the poor chainlines 1x demands at either end of the gear range.

This might not be at all good with a triple -
the larger overall tooth difference, and wider varying chainline are outside its designed parameters, which are pretty strict.

Rear cassettes have such wide ratios now that you can get a huge overall range with a double.

Mixing shimano groupsets up gets worse results with the bigger numbers of cassette sprockets - even when they ought to be compatible, like mtb 10&11.

But different riders have widely varying tolerance to fussy, clunky or problematic shifting, unusable gears and baggy or too short chain.

And many love a challenge