https://bike.shimano.com/en-EU/product/component/alivio-m4000/RD-M4000.html says that derailleur will handle Low
sprocket_Max. 36T Low sprocket_Min. 32T ANSWER : You cannot run a 50 tooth cog with that derailleur.
You might be able to use a hanger extension, but that will make the small gears even worse.
Wolf Tooth's Roadlink allows up to 40 tooth, and Wolf Tooth's Tanpan says 44 or 45 tooth is the maximum cassette size supported.
Note
these are for 10 and 11 speed.
If you're absolutely stuck on a 50 tooth rear cog, then you're looking at a SRAM 12 speed Eagle setup, which will not be cheap.
Cassette and shifter must change, and its very likely your freehub won't fit the cassette, and then the OLD will be too large to fit in your frame.
Not a good plan.
bicycles.stackexchange.com/users/19705/Criggie
Derailleur will not handle that, as Criggie says in his answer.
Apart from that, an 11-50 9 speed would have horrifically big jumps between gear ratios.
1x systems only really became feasible with the advent of 11 speed drive-trains, and still sacrifice ratio jumps to get a full spread of ratios to some extent.
If you really want a 1x 9 speed, get a cassette a 9 speed derailleur can handle, then get a small enough chainring to give you the low gears you want, and forgo the higher gears.
BTW, Shimano provides tech specs for all their products (as Criggie linked to).
This page is a good place to start looking for specs of a particular product.
bicycles.stackexchange.com/users/24228/Argenti Apparatus
I run a shimano m4000 with a 9spd goat link on a 9spd 11-50t cassette with no problems b screw doesn’t need to be fully wound in.
More recently, I’ve reverted to a 10spd SLX shadow+ mech sgs cage which I run with a sram x7 9spd shifter, giving even better shifting.
bicycles.stackexchange.com/users/40653/Andy W
I have to agree with Dave - 11-36 works like a charm, gear spacing is just right.
A 11-40 cassette just works OK with the B-screw screwed in all the way or using an even longer replacement screw.
I also tried an 11-42 which didn't really work well.
AFAIC the issue with the wide range cassettes reg.
9-Speed is that they have the cassettes but there are no (Shimano) derailleurs to shift it.
At least not out of the box.
You could try a Shimano 10-speed derailleur and if it doesn't work ok (which it likely won't), try tweaking it.
There are howtos online with re-routing the cable for a different pull ratio.
11-speed derailleurs might be too narrow, chain-wise.
You could also use a Sram 9-speed shifter with a Shimano 10-speed derailleur.
Trouble is, all of these solutions are rather expensive if you haven't the parts in the spares box.
Rather than spending that much money on an exotic 9-speed solution that doesn't get better over time, invest it in a Sunrace 11-speed cassette and Shimano SLX derailleur plus shifter.
What you don't want is a solution based on hanging your derailleur lower and the Wolf Tooth link extensions don't work with 9-speed derailleurs.
I tried it (and it's rather expensive too).
Best to stick to inexpensive 11/12-36 and a 30 or 32 NW chainring.
Or try the 11-40, but that's the max you will be able to get working properly.
bicycles.stackexchange.com/users/40420/Simon Adventures
21% gear spacing is not a problem.
Shimano has over stated the need for tight ratios.
The shifting won't be quite as smooth, I have an 8spd 11-40, but will be well within acceptable standards.
11-36 has never been a problem with 9 speeds and I usually have to double
shift my 11-36 10 spd because the ratios are too tight.
You will have to use a hanger extender with a long cage derailleur.
The warnings that the extender doesn't allow the RDR to track the cassette properly is also over stated.
Shimano claims they do no testing with components other than their own.
If you believe that Shimano wouldn't know.
Obviously that is ridiculous.
Shimano has stubbornly lagged 2 to 3 years behind the market in the area of gear ranges.
They don't belive in it and only participate well behind the market because they have no choice so pick another brand of RDR.
There are many options.
bicycles.stackexchange.com/users/39946/Dave
I looked at some offerings of such cassettes and what a vendor suggests as a derailleur for them.
An example of a cassette: Compatibility chart from the same page:
It looks that no 9- or 10-speed dérailleurs are compatible with that cassette, but they claim that some 11-speed ans 12-speed parts from both Shimano and SRAM may be used instead.
bicycles.stackexchange.com/users/26917/Grigory Rechistov
Box Components have released a 9-speed 11-50 drivetrain (cassette, RD, and chain) for EMTBs (thicker chain and cassette to cope with the torque), and I think the gear jump ratios don't matter when it comes to mountain biking.
Even Seth's Bike Hacks uses it, and he's a very nitpicky kind of guy.
What I don't know is if it's compatible with a standard 9-speed system.
Box Components says it isn't compatible with Shimano and SRAM 9-speed systems, but I have a feeling they're just saying it for marketing purposes.
bicycles.stackexchange.com/users/39963/Gregory Leo
I have used a RD-M2000 and 11-50 on 9 speed with hanger, but the very connection of the gear wire on the inside just touches the bigger cog when in 1 gear, otherwise ok (almost :-)
Would probably try the RD-M370 instead next time
bicycles.stackexchange.com/users/43823/Max
I'm trying to understand if its possible to fit a 9-speed 11-50T cassette (found one on Ali) on my MTB. The plan is to go 1×9. The problem is that I can't seem to understand the if a specific derailleur can handle that.  The rear derailleur in mind is Shimano M4000 long cage. Should I use a hanger extension? Will 11-42T be better for that?  Thanks for the help
Fitting a 9-speed 11-50T cassette on MTB: which derailleur?
bicycles.stackexchange.com
<mountain-bike><derailleur><cassette><derailleur-rear><compatibility>
bicycles.stackexchange.com/questions/54476
bicycles.stackexchange.com/users/33332/user3510526
A number of derailleurs are recommended when fitting a 9-speed 11-50T cassette on MTB: Wolf Tooth Roadlink and Wolf Tooth Tanpan, SRAM 12 speed Eagle setup, Shimano 10-speed derailleur, Sunrace 11-speed cassette and Shimano SLX derailleur. Note that Shimano states it does not test on components other than their own. A 9 speed cassette is unlikely to support a large range, so switching to an 11/12 speed might be a better option. Having said this, some commenters claim that Shimano overstates the problems with wide gear spacing, and that this setup could work with a hanger extender and long cage derailleur.
A 9 speed cassette is unlikely to support a large range, so switching to an 11/12 speed might be a better option. Some commenters claim that Shimano overstates the problems with wide gear spacing, and that this setup could work with a hanger extender and long cage derailleur.