Shimano Deore XT 9-speed rear derailleur with 9-speed 11-46T cassette?

Question

I have an early 2000's bike with a 3x9 drivetrain. The front is a 22-34-44. The rear derailleur is a Shimano Deore XT RD-M750 and the cassette is a SRAM PowerGlide II 11-34T.

I'd like to change to a 1x9 and am trying to not spend very much. I have the following in mind:

• Replace front with a narrow-wide 32T chainring
• Replace the rear cassette with a 9-speed 40T, 42T, 46T, or even 50T cassette
• Keep the existing derailleur and chain

My concern is the rear. I realize these big cassettes have big jumps, and am okay with it. What I am not sure about is whether they can be mechanically used with my existing rear derailleur, after B screw and any other adjustments.

Anyone with these components or experience that can give guidance?

Answer 1

I would not recommend using that derailleur. In the early days when 1x large cassettes were new, they were pricy, and people wanting a budget option had to hack together something, mostly ending up with something that kinda of worked some of the time. These days there are a range of cost effective products designed for the large cassettes.

As you are buying a new cassette and front chainring, the cost of upgrading the entire kit would be money well spend. Have a look at third party manufacturers such as Microshift (Advent range). These do not offer the XTR level performance, but will easily exceed the performance of an old XT 9speed on a 11-46 cassette.

Answer 2

The specs for the GS are found on Page 3 of https://productinfo.shimano.com/download?path=pdfs/archive/2005_SPECIFICATION.pdf and the SGS are on page 4.

Those specs say that this mech can go up to a 34 tooth rear regardless of the cage's length. Shimano's specs are notoriously conservative, but any more than 34 is officially outside the limit. I'd expect 36 to work fine, and 38 is likely to be okay.

40 and 42 would be pushing it a lot, and any more is unlikely to work.

Why have a GS and a SGS version? the SGS allows more "capacity" of 43 links vs 33, so you can have a triple chainset with a SGS.

You can get an extender for your derailleur hanger called a Tanpan or a Wolftooth Goat Link, but they're a compromise on the higher gears with fewer teeth engaged, and more wear.

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If you can afford it, I'd suggest a new cassette and rear mech specifically able to cope with the wide range. You could also get an extra gear by switching to 10 speed, but then you definitely need a new shifter too. A new chain will be required, but your existing narrow-wide chainring should be okay.

Store the takeoff-parts in case you want to revert, or give them to a bike coop/fixing person. Don't throw them away.

Answer 3

For a 1x drivertrain, my recommendation would be to change the rear derailleur too.

Two reasons. Firstly, 1x drivetrains generally have the same small sprocket as 3x drivetrains. Thus, to be able to go at any decent speed, the chainring has to be large too. The only way you can climb up hills with a big chainring is that the largest sprocket is very big. This requires a rear derailleur that supports such big sprockets in a cassette. Any 3x rear derailleur has limited big sprocket size. The capacity would be enough (usually 3x drivetrains have around 1:1 as the lowest gear, so for example 28T-38T-48T and 11-28T has 4.36x difference in largest and smallest gear, and to approximate that you'd get something like 11-46T and 46T chainring which requires 35T capacity, very similar to 37T capacity of the 3x system), but the slant parallelogram in the rear derailleur needs to be more slanted to support big rear sprockets.

Secondly, a narrow-wide chainring is not enough to prevent chain derailment at the front. I have a fatbike with narrow-wide chainring and clutch rear derailleur. After buying it, I was not aware of the fact that the clutch needs to be turned on (it was off from the factory). About 100km riding and I had a chain derailment. There being no front derailleur, it was impossible to raise the chain back to the ring without getting my hands dirty in chain oil. Note my derailleur with clutch off approximates a non-clutch derailleur. You don't want that, so you want to have a clutch derailleur and also remember to turn the clutch on.

An alternative maybe could be to retain the front derailleur, making it less likely to derail (because the front derailleur acts as a chain guide), and if it derails if you retain the front shifter too, it might be possible to raise the chain back to the ring without getting your chains dirty.

So, the rear derailleur should optimally be changed.

Answer 4

As the others, I also think that it would be better to upgrade the whole drive train or maintaining your current setup. There would too much compromises in cost saving, and you will end up with something that won't work as well as your current setup.

Doing a 1x with your current XT is clearly out of its design specification, and also recent Deore/Advent are more advanced than an XT of this generation (thinking about the clutch in particular, that is more than a "nice-to-have" with a 1x setup).

About keeping your chain: a 32/50 requires a longer chain than a your current 44/34 (and anyway if you chain is worn, you can't use it with a new cassette).

If you want to go so wide with 9 gears, there's also another issue: sourcing. The only possibility is Microshift, that is not widely distributed and the availability of parts is random. Microshift Advent shifters are also using their own pull ratios, so if you were to use an Advent derailleur, you won't be able to reuse your existing shifter. Price-wise, it won't be much cheaper than a Deore M5100 if you were to upgrade the whole drivetrain.

But if you can afford it and are willing to upgrade the whole drivetrain, a good thing to know is that some retailers are offering bundles with crankset, chain, cassette, shifter and sometimes bottom bracket, that can be cheaper than buying the components separately (and you can be sure that everything is designed to work together).

Answer 5

I'll share with you my experience changing aspects of the drivetrain on my '02 Stumpjumper. While I am a "Shimano guy" for several reasons, other manufacturers have offerings that will work well and rather than product endorsement, it should be taken as what I've done. One caveat: mixing brands of drivetrain components, specifically, rear shifters and rear derailleurs, is typically NOT recommended.

The above Stumpy has a 2x10 drivetrain, 34-24 front, 11-36t cassette. Shifters are Shimano SLX 10 speed, with the left being able to switch from 3x to 2x. My gearing ranges from a low of 0.66 to a 3.06 high. Your proposed 1x gearing is 0.8 low 2.90 high in comparison. The broader range is one reason I like 2x. Mountain front derailleurs can be sourced for little of nothing these days, and set-up, shifting and shift patterns is easier than ever. I typically ride the big ring exclusively, but either way there is no chain rub and despite the cross chaining, this isn't such an issue these days with 2x systems and narrower, flexible chains made better with wear and friction reducing materials. Also the large-large cross chaining, which is common with a 2x mountain system is the lesser evil anyway.

Arguably, two things are necessary for a 1x system to function with any degree of acceptable performance: a narrow-wide chainring and a clutched rear derailleur. Due, in part, to the chain guide action of the front derailleur's cage being absent in 1x, chain retention is a necessary consideration for these systems. The narrow wide ring prevents side to side movements of the chain that can lead to derailment. The clutched rear derailleur has a setting that prevents movement of the derailleur cage when the bike encounters bumpy terrain, thus preventing the chain from becoming momentarily slack. As has been pointed out, the RD-M750 lacks this capability. In addition, Shimano trickles down the technology developed at the highest, XTR, level of components to the mid-range line up in fairly quick succession. Thus, today's Deore lineup was yesterday's XT/XTR as evidenced by Deore being 12 speed with Shadow+ design derailleur's initially only offered at the XTR level. Point here is the older XT derailleur, while still decent in quality and performance, won't keep pace with the new Deore. I can attest first hand that the M750, which I owned, failed in an experiment when I was feeling out turning a hardtail into a 1x with a chain guide and 11-40t 9 speed cassette from SunRace. It couldn't climb the chain onto the large cog even with the B-adjust bolt turned around (for maximum length to create maximum distance between the cage's jockey wheel and the cassette's large cog). One could use a goat link or like product to extend this gap, but you'd still lack the clutch and have trouble getting the 11 tooth cog to work.

You could get a 10 speed 2x crankset and maintain much of the range you have with the 3x. A 2x front derailleur is not expensive and your current left, front shifter can still be used as the 2x crankset uses the middle and small ring positions you'd simply toggle between 1 & 2 at the shifter. When your budget allows, turn everything over to 1x11 by getting a narrow-wide chainring of the same BCD as the 2x crankset, a right 11 speed shifter and rear derailleur and 11 speed cassette. Twelve rear cogs may be a problem for two reasons. First it requires a compatible rear hub, meaning a new rear wheel which would arguably be the highest priced single item of a conversion. Second problem may be rear triangle spacing if it is 135mm. I believe I'm correct in saying there isn't enough space there for a twelve speed cassette and anyway you won't easily, if at all, find a 135mm rear hub sporting a microspline or XD driver required by a 12 speed cassette.
Also mentioned by others is the option to buy a 1x11 group set having all the components and new chain necessary to convert. The used market is fairly brisk right now and your current XT derailleur still fetches a price that shouldn't be scoffed at.