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I need your help about gear ratio.

I am currently riding 3x9 drivetrain, Deore m592 rear (SGS-Shadow), Deore XT m770 front.

My gear ratio is: 11t-32t (rear) and 22t-34t-44t (front).

My local hills and trails consist of hard uphill and some small downhill tracks. The hard uphills are the reason why i want to make a change in my cassette ratio.

I am planning to upgrade to a bigger, 11t-40/42t cassette, but I'm confused if this is possible with a 3x system or not.

I've read that the max cog (rear) for some derailleurs (including my SGS Deore) is 36t, but a lot of people say that 11t-40/42 or even 46t is possible. Are these cassettes too large for a 3x9 drivetrain? Do I need to convert to a 2x in front as well?

Will a hanger extender + the b-link somehow make it possible to get the cassette size i want?

Any help would be appreciated.

Thanks in advance :)

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    You could. The real question is if you should. Any 3x + 11-42 is a bodge up with parts not made to work together. It can be made to work, but what does 'work' mean? '"works, sort of, most of the time" or 'Just works, 100% all the time, every time" To answer 'should' we need to know 'why do you want to do this?'
    – mattnz
    Nov 5 '20 at 19:02
  • Here, the local hills, trails and nearby mountains consist of very steep uphill. That's the reason for an upgrade. Will a hanger extendor + the b link help increase derailleur capacity and help me get 11-40/42t? Thanks in advance
    – user53666
    Nov 6 '20 at 17:49
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    I ride a 26er triple with 24/36, can't imagine going to a lower gear as its easier, safer and faster to dismount and push the bike once you down to that speed (5km/h @60rpm cadence). Consider if a 11-36 cassette which gives you 'one lower' might be a compromise between low enough and works reliably
    – mattnz
    Nov 6 '20 at 20:51
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It's not clear why you would want to use an 11-42 cassette in a 3x drivetrain. 11-42 cassettes are typically used with 1x or 2x systems. With a 22 tooth chainring and 34 tooth sprocket you already have a pretty low gear ratio (0.65) - lower than a typical 1x drivetrain with a 30 tooth chainring and 11-42 cassette (0.71), and only a little higher than a 2x 36 tooth small chainring and 11-42 cassette (0.62).

Just to give you a definitive answer on compatibility: the two derailleur specs you need to know about are the max cassette sprocket size and the total capacity. Max sprocket sizes is obvious, total capacity is the ability of the derailleur to take up slack chain and needs to be greater than or equal to (difference in largest/smallest sprocket size) + (difference in largest/smallest chainring size). Your current setup requires capacity of (34-11)+(44-22) = 45.

You can find Shimano specs here: https://productinfo.shimano.com/#/, in the archive PDF spec sheets. The M592 SGS has max sprocket of 36, total capacity of 45 - which obviously precludes a larger range cassette.

If you used a Alivio 2x9 crank with 36-22 rings and a 11-42 cassette the capacity requirement would be (42-11)+(36-22) = 45, but your derailleur still can't handle a max cassette sprocket over 36 teeth. (Although, I've heard of people successfully using a derailleur hanger extension to accommodate a large range cassette.)

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    A 22x42 would be an extremely low 14.5 gear inches. Pedaling at 90 rpm, you'd barely be going walking pace, and might have trouble keeping the bike upright.
    – Adam Rice
    Nov 5 '20 at 18:43
  • Between 5 and 7km/h to be precise
    – Michael
    Nov 5 '20 at 19:05
  • @AdamRice my folder is about 15.7 gear inches in its lowest, and its fantastic for pulling heavily loaded trailer. I've successfully moved 100 kg of UPS that way, with a climb to a railway crossing en-route. Definitely not needed for normal riding, even a 30% grade doesn't need that low gearing.
    – Criggie
    Nov 28 '20 at 5:25
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ah, a person after my own heart.

Confirmed yes, it works, it's real, and it's fantastic.

I have 3x9 setup, with the exact same RD. 22-32-44 up front, 11-46t in back. That's a range of 836%. With a measured 52mm tire and 165mm cranks, that's 13.8 gear inches. It's pure uphill loaded touring bliss.

My experience was that 11-40t works fine with the road link extender, but it struggles with a 46t. It functions, but not well. However, I got the extra long extender for a mere $9.50 and the 46t works great. Seriously, that little piece of metal let's you spin to your heart's content (70 RPM at 2.8mph) for less than the cost of lunch.

Side note, I've found the b-screw barely matters. I think shifting would be fine without a b-screw.

In case you're wondering, yes, of course, when the 11-46t wears out, it'll be replaced with an 11-51t. Also, in the off-chance that your bike has bar-end shifters, as mine does, unsolicited, consider a friction/downtube setup. With less/no cable drag, shifting is effortless. It doesn't even require an opposable thumb.

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There are two things to be aware of here, three if you consider the hack.

First, it seems you have already considered max cog size. This will affect whether or not the derailleur can get the chain up onto the biggest cog. Technically, you need to be aware of minimum cog too, but you have an 11 which is arguably the most common for MTB. I assume this is for MTB based on the drivetrain you have described.

Second, you also need to determine max total capacity. This will determine whether or not the derailleur can take up all the chain slack when you are in your smallest gears. The post I have linked below does a pretty good job of explaining it. Once you know you proposed new maximum capacity, you can look it up on the shimano website for your (or any) derailleur. How to calculate the capacity of a rear derailleur

Third, let the hacking begin. If your numbers work, you are good to go. If not, whether or not you proceed really depends on you. Personally, I am the kind of guy that would go for it. I love tinkering with bikes, when things don't work out I get frustrated, but the process of what I learned, and the process I go through is worth it to me. It is my hobby, and I love it.

For others that just want something to work with minimal energy, it is a very different risk of your time and possibly money.

On two occasions I have made a RD work with a cassette that is technically to big for the derailleur. The first time was a Sram XD (I think XD anyway) rated for 42T and I got it working with a 46T just by cranking the B screw way out.

The second time, I was using a 10 speed system; a shimano derailleur designed for max 36T, and got it on a 46T cassette. This project took more tinkering. It did not work at first so I tried one of the derailleur hanger extenders, which made it work mostly. The shifting was not as good as I would have liked but it was for my son who was growing so fast at the time and I knew it was a temporary solution. It also may be worth noting that there was some previous damage in the derailleur from an attempted trailside re-straightening attempt.

Regarding hacking chain slack. My first hack I mentioned above was actually on what I call "Ben's personal 1.5X drivetrain". It was a 11-46 on the back combined with a 30T and a 26T up front but with no front derailleur. This bike was for my daughter who was very put off by the difficulty of climbing. The 30T was for riding around the neighborhood and just being a kid. Then, we would manually put the chain on the 26T cog if we went out to a trail where there would be some steep (from the perspective of a 10 year old) climbing. On the 26T chainring and the 11T cog, there was too much slack, but somehow it worked out, and it was pretty rare for her to actually be in that combination.

Again, if and how you hack is very much a personal thing. I love it and I have fun with the challenge of trying to get things to work when they don't. Others would consider it a loss if things don't quite work. Whether or not you embrace that risk is entirely up to you.

Good luck.

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  • To be honest, I don't really feel like doing the math for you, but my guess is you'll be OK putting the 42 on there, but need to lengthen your chain, which will cause too much slack when you are on the 22 in front.
    – Ben Stokes
    Nov 5 '20 at 17:59
  • Hello, thank you for your advice. I also think that 11/42 may be possible. But how about a hanger extendor, combined with the b-link? Will this actually increase capacity and give the 11-42t cassette a "green light" (a.k.a "you are good to go") ? The main reason for an upgrade is the very steep uphill of the local hills, trails and the nearby mountain paths. Thanks in advance.
    – user53666
    Nov 6 '20 at 17:51
  • I am not familiar with the term "b-link". The derailleur extender I used was basically to increase the distance between the jockey wheels and the cogs. I think it will probably work to allow the chain to get up onto the biggest cogs, but it does leave you with the other problem that there will be too much chain slack when you are in the smallest gears. Also, I agree with another user that 22 in the front with 42 in the back may be such a high ratio that it is not really practical. I have an excel gear ratio calculator that I made a long time ago. Let me see if I can find it.
    – Ben Stokes
    Nov 6 '20 at 20:08

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