PDKL45

So there's a new 11-40 9-speed cassette from Sunrace, the CSM990 (SunRace | CSM990).

I am very keen to go to 1x9 on my Specialized AWOL at some stage in the future--probably when my FSA Omega Triple gets a little more worn, and/or the MegExo BB gives up the ghost.

I am wondering if anyone knows how I can calculate the required total capacity of a derailleur for a 32t chainring with an 11-40 cassette? I already have a 9-speed Deore M591 rear derailleur, but with Deore going to 10 speed, I might have to use an Alivio T4000 by the time I get around to converting. I have flat bars, so there is no problem with road shifters etc.

Would either of those derailleurs work (or an XT M772 for that matter)? They are all 9-speed and have a total capacity of 45T.

JonathanGennick 

You will need 29 teeth of capacity. 40 - 11 = 29.

The 40 tooth cassette cog would worry me. I checked Chain Reaction Cycles' website, and the Alivio is listed as supporting a max cog size of 34 teeth.

PDKL45

It worried me too. I was thinking that was with a front triple crankset, though, so it might fly with the single chainring. The worry for me was there not being enough room below the 40t cog.

I need to get more up to speed on 1x stuff.

JonathanGennick 

The issue w/max cog size is the derailleur itself. As the derailleur moves from outside to in, it extends to accommodate large cog sizes. Derailleurs are designed for common cassette profiles, and a 40 tooth cog was not in the mix back in the nine-speed days. The person designing that derailleur did so with a max of 34 teeth in mind. I bet you could get away with 36, but 40 seems an awfully big leap.

Edit: Found this thread on mtbr that might prove helpful: https://forums.mtbr.com/drivetrain-sh...te-908804.html

Bike Gremlin

I'd say stick with a triple if you need all that gearing range. That being a technically more sensible option IMO.

PDKL45

I still may stick with a triple, but my crankset is currently 30-39-50 and it's a bit high. A 30 or 32T chainring on the Sunrace 11-40 9-speed cassette would cut about three gears off the top of my current range--I have a 12-36 9-speed cassette at the moment--but would give me a little more on the bottom where I need it.

I have to admit that I'm not a huge fan of the shifting of my road triple crankset and I like the idea of reducing redundancy in my drivetrain. Plus, the CSM990 is a relatively cheap component and trying it out will not break the bank.

JonathanGennick 

Maybe a double? Is that possible? I'm not fully up to speed on road-bike drive trains.

Sometimes it's worth taking a shot if you don't mind experimenting. I bolt together parts all the time, and often will just try and see whether some combination will work.

PDKL45

I could go with a double MTB drivetrain, but I quite like 9-speed for its durability. Plus, I sort of feel like experimenting with a 1x9 and the new Sunrace cassette will allow me to do it. One cassette is about half the price that a 40t expander cog was a year or two ago.

There's also the issue of my knees, which have some recently diagnosed cartilage damage that may be the beginning of osteoarthritis. My doctor has recommended cycling on flat ground with high cadences and spinning up hills without standing, so lower gears will help with that. I need to take as much pressure off my knees as possible. It is a bit of a bummer, but we all get older and have to adapt to changing circumstances.

9 speed stuff is also agreeably cheap and I have become something of a retrogrouch for recently "superceded" bike components like 9 speed drivetrains and QR dropouts for road and light doubletrack riding.

There's no huge urgency to the change, but I am very seriously considering it and starting to work out how I can do it and maybe build a small stash of parts.

corrado33

Sorry, going to a 1x when you have bad knees and freely admit that you need lots of gears sounds like a stupid idea.

1x drivetrains are really for strong riders who can power up hills, or for somebody who never wants to go faster than 20 MPH.

You've convinced yourself that a 1x is a good idea. Take a step back and look at it again.

The problem, as someone mentioned above, with the max tooth size limit on a derailleur has nothing to do with the front chainrings. Derailleurs have a hard maximum for the largest tooth cog they can accommodate. Anything above that and the derailleur itself will plow right into the large cog when you're shifting.

PDKL45

I'm fine with 20mph and below. I ride a heavy steel bike that I don't race and there is always an N+1 if I want greater speed. Going back to a 3x9 set up would also not be out of the question.

I have convinced myself that 1x9 is an interesting idea, worthy of consideration. It may never happen, but I am not going to dismiss it out of hand.

Derailleurs do have the largest tooth cog they can handle, that's true, and in my original post I probably hadn't thought things through properly vis-a-vis derailleurs. A Wolftooth Roadlink with a medium cage derailleur may work, but I'm sure it's not the only solution. A poster at MTBR was using a Shimano Zee derailleur with a 1x9 drivetrain just fine in a thread I saw earlier. Plus, I'm sure someone at Sunrace may be able to suggest a derailleur I can use.

fietsbob

Experiment..

Perhaps you need all the parts that are being combined in the new trend of cassettes with really big low gear cogs.
Study what combinations they have.

I used a Chorus short cage with a 14~34t freewheel . having 1 chainring means the tooth difference is just

in this case, 20 t , there is no additional wrap up needed because there is no difference between 2 chainring sizes.






.....

Mr IGH

If you want a lower gear, swap the inner 30T chainring for a 24T. It's a 74mm BCD, there's plenty of options under $20.

Bike Gremlin

If that's too high, you could get a (cheap) MTB crankset and FD. 44-32-22. Though it might work fine with the current FD as well, just slightly slower shifting.

If say 30-32 combo is too high a gear for you, what 1x chainring were you planning to use with 11-40 cassette?
34-40 gives roughly the same gear ratio as 30-36. So with 1x you'd end up with too little gears for fast riding, while gaining nothing for easier climbing.

hueyhoolihan

loaded touring, for nine months, on a 1x7 with a 32t large cog and 36t chainring is doable for at least one mid 40 year old rider that i know of. and he ain't no athlete, i can assure you. he said the simplicity of a 1x7 was refreshing. YMMV.

IME, the key to getting a low gear is to get a crank that can take a single small chainring. anything in the 30's should do. it will simplify things. then the rear derailleur doesn't have to be something special to accommodate an outrageously large rear cog.

Darth Lefty 

Sunrace has had an 11-36 for a few years now, and Shimano has started this year with ones at Alivio and Acera level. That would be less of a challenge for a regular old SIS mountain bike derailleur, which are usually rated for 32t or 34t cogs and are known to maybe address a 36t if you turn the b-screw around. 36 is a pretty big rear and gives you an overall range of 3.3:1, pretty good, can you match the low and sacrifice the high gear? Only the last generation of 9-speed, Shadow-style SIS MTB derailleurs like M592 or the current Alivio are rated for 36t cogs, and I haven't tried one on a 40. You can get to a bigger cog with a product like the Goat Link. Pretty much any medium or long cage RD has enough chain wrap for a 1x system.

You also have the option of going SRAM to get a big 1x system and a brifter. But it's a bunch more parts than just swapping the cassette.

PDKL45

Thanks Darth Lefty, your info on derailleurs was helpful. A Wolftooth Goatlink (Edit:a Roadlink might be better) seems to be a solution.

36 is a big rear. I would gain some development (or GI) with a 30 or 32 tooth chainring and do not really mind losing my three top gears, in that I do not use them outside of descending up in the mountains.

For me it would not be a exercise in lowering gears, so much as a way to reduce complexity and redundancy.

It remains an idea for now, and a 38 or 40 tooth chainring on the Sunrace 11-50 cassette would onviously offer more range, but components are a lot more expensive in the 11 speed realm.

PDKL45

Good info, thanks for that. I was thinking a 32 chain ring with the 11-40 cassette, as the 32-13 gear would be very close to the 50-21 gear, right in the middle of the cassette, that I almost always spin in at the moment.

nfmisso

This spring I assembled my mid '90's Trek 720 commuter with a 1x9; using a USAmade 44T wide-narrow chain ring, Shimano HG300 12-36 cassette, SRAM X.7 9 speed long cage (36T rated), X.0 9 speed shifter, KMC X8.93 chain. I am very pleased with the results. The 44/36 ratio is just right for the one short steep hill I have to deal with, and 44/12 is plenty for the slight downhills and afternoon tail winds.

Please NOTE that a RD's maximum cog size is based on a nominal rear axle position and a nominal hanger bolt position - both of which have tolerances of ± millimeters. SRAM recommends a 6mm upper jockey wheel to big cog clearance. When I first put the X.7 on, there was about 12mm clearance; more than enough for 40T; and the B-screw was in the middle of its range!

I recently purchased a Sunrace 8 speed 11-40 cassette, for another project, which I am just starting. It is for a friend, who will be pulling a trailer with her dog in it, rather low speed stuff. It is getting a 38T chain ring, X.7 again. It will be a few months before that gets done.

I have become a great fan of 1x9 drivetrains after building one as an experiment, and really liking it. Originally, I had planned a 2x8 with 52/39 and 14-32 cassette. The 1x9 with 44 and 12-36 is a very close match.

Bike Gremlin

44-32-22 crank, with a widely available 11-32 cassette works fine and simple. Giving a wider range than a 1x setup, with most readily, widely and cheaply available cassettes and RDs. Also allowing for less cross chaining. That is what front chainrings do - add gear range, without needing wide gaps between adjacent (rear) cog sizes to provide that, without having the chain run crossed on highest and lowest gear and requiring too many cogs to do all that. It is a simple, proven design that works.

Having 1x setup with a wide range cassette is the less simple solution IMO. To me it's similar to trying to make a car without a gearbox, trying to make an engine with a wider range of RPMs providing high torque (electric motors aside - they do that without problems), if you understand my analogy. With a 1x, instead of a 2, or 3x, you need a very wide range cassette, very long cage RD, sometimes hung lower than it is standard with an adapter, sometimes with and added front side chain catcher to prevent chain coming off the (front) chainring.
It also has you riding with a very few teeth involved on most flats. 30-11 combo will wear out a lot faster than say 42-15 (those two have similar gear ratio).

As for "redundancy", if avoiding that is a goal by itself, no one can argue it, though a compact 2x drivetrain is good at avoiding redundancy - and some don't find it practical exactly because of that - it requires a few back shifts after one front shift in order to stay in a similar gear range as before the front shift. Of course, 1x doesn't have that particular problem (and neither does a standard dobule, or a triple, but they do have the "redundancy" of gears).

PDKL45

Looking around a bit more, it seems that people have had good results using Wolftooth Roadlinks with MTB derailleurs in 1x8 and 1x9 drivetrains to drop the top jockey wheel down enough for there to be no rub with the 40 tooth cog. That would vary with the different derailleur hanger lengths of different models of bike.

Going to a 1x9 drivetrain remains only a possibility, but it is interesting to see how contentious the whole idea is. I only really came around to the idea myself after playing around with the HTML gear calculator and seeing just how much redundancy there is in a triple drivetrain. It was also quite unexpected as to how few gears you potentially lose off the top with various configurations. I guess I have accepted that the idea has merit, but I do understand why some don't.

Bike Gremlin

Redundancy gives no harm by itself. Quite contrary. For example:
If there's a hill coming up, you can have a gear ratio you like using the middle ring. If there's a downhill coming up - you can have the same gear ratio from the big ring. In both cases, you can make the big change up front in time, then fine tune by just changing gears at the back. A drivetrain without "redundant gears" won't allow that.

Just in case you didn't come across this one, it's a great quick way to check gearing before actually changing it:
Bicycle Gear Calculator

nfmisso

Try it, then decide.

All of the above arguments against are theoretical, they have not tried it. Most (not all) people who try 1x drivetrains like them.

I do feel that a wide-narrow chain ring is very important. I use this one: https://usamade.myshopify.com/collec...wide-chainring on my 1x9; it starts out a bit noisy, and you can see it pull the chain onto the ring when the chain is at the maximum angles.

Bike Gremlin

IMO, it's partly due to the hype of 1x drivetrains. Investing time, effort and money into this "improvement". In my experience, people are happy when they buy new, expensive things, even if they don't really work any better.

PDKL45

I don't know that it will be all that expensive really. A narrow-wide chainring for around $45.00, a cassette for around $37.00, a roadlink for around $22.00 and some reasonably cheap chainring bolts. I have some 9-speed chains that were on sale and an old XT crankset with worn out chainrings in my spare parts stash. I can have a 1x9 conversion for about the cost of a replacement road triple crankset if I decide to go in that direction.

I am happy when I have time to do the things I enjoy, like riding my bike for a hundred and fifty kms or so, rather than when I have new things. I agree that a 1x9 will not work any better than my existing 3x9 drivetrain, but I would prefer to know what it's actually like to ride in practice than to merely think about it and wonder what could have been. It's not an improvement so much as trying something new and different.

A little of my wanting a 1x9 set up may be down to the "hype" surrounding 1x drivetrains, but a lot of people seem to like them, and I might just try one out for myself to see how I like it. There is also the fact that the necessary components are now much more readily available at a cost effective price.

hueyhoolihan

there's really nothing to it. simply remove the FD from your bike, pick a chainring and go. and if the gearing is not satisfactory, move to another chainring.