anga

Please don't start discussing the need for this combination and alternatives.

Highest I have seen so far is 45.
Are there any rear derailleurs (8- and 9-speed only} that have higher total capacities?
Thinking of 12-40t, 8-speed cassettes and triple crankset.

FBinNY 

2 suggestions IN CASE you cannot find a derailleur that meets your needs.

1-you can increase the take up capacity of any RD by substituting a larger idler pulley. It's not much but better than nothing.
2- you can exceed the take up range, provided you run a chain long enough to loop the big/big combo safely. You'll have sag using the granny with the smaller cassette sprockets, but are unlikely to use those combos anyway.

anga

Thank you. I was unaware of these workarounds.
For the second, I certainly do not need to use the smallest chainring with the smaller cogs.

Main motivation is using the small chainring with the larger 30+ cogs and get 3 or 4 additional lower gears. Higher gears don't matter. Can even start with 14t or 15t, but for the RD limit on the maximum size of smallest sprocket.

​​​​​​How does the capacity of the RD increase with size (number of teeth?) of idler pulley?

Hondo6

Microshift indicates their Advent 9 RD has a total capacity of 47T. But it's not Shimano-compatible, so you'd need one of their Advent-family shifters to use it. And I don't know if they make a triple FD.

70sSanO

Generally Shimano's RD capacity is conservative. Exceeding the max capacity, and by how much, is also a bit of luck.

In addition to the actual tooth count, the chainstay length does impact how much "luck" you have whether the chain length is truly maxed out in the big-big, or you can take 2 links (inner & outer) and still have enough chain length for the chain to climb onto the large cog while in the large chainring, you might be able to run a small-small.

If you have the a chainstay that is 1/4" longer you might not be able to do that and the small-small without the RD cage folding back on itself, which is generally not a problem unless there is significant sag.

If the chainstay length is 1/2" longer you might be back to running the small-small.

Of course anything in between exact chain pitch differences and it may or may not work, after all it is blind luck if if you can push or not push capacity and by how much.

Swapping a chainring, or small/large cogs with different tooth counts throws everything out for better or worse.

John

FBinNY 

Chain take up is determined by the sweep of the derailleur cage, whose effective radius is measured from the pivot to the chain (not to the pulley's center). So it's about the sum of cage length and pulley radius.

I mentioned the option of using inadequate take up so you'd feel free to choose a derailleur without limiting yourself to those of highest capacity.

However I remind you that the shortfall MUST be at the small/small end. It's absolutely critical that the chain loop the big/big combo even if you're sure you'll never shift into that. The MINIMUM consequences of accidentally shifting into a combo where the chain is too short is ripping the hanger of the frame, though they could be much worse.

FBinNY 

Sorry, but no.

Take up capacity is only based on the 2 variables; arm sweep, and change in RD angle (on RDs not at fixed angles to hanger).

Since chainstay length doesn't change when shifting, it cannot determine capacity in any way.

That said, long chainstays and/or large sprockets can demand chains longer than the typical 114 links of stock chains. A consideration easily managed by splicing 2 chains.

3alarmer 

...if your main purpose is to obtain lower gears, I'm not certain I understand why you wouldn't put a smaller chainring on the large position in front. Thus reducing the total chain slack your derailleur will need to take up. Perhaps I am missing something in your gearing equation ?

70sSanO

I realize the chainstay length doesn’t change on the same bike.

It is a bike to bike difference. Some people with the same RD can push past the max capacity spec and some can’t.

The chain is limited to 1” increments.

John

FBinNY 

It's a possible consideration, but can usually be worked around by tweaking the B-screw. But, as you point out, the conservative (worst case) published take up capacities leave some fudge room.

The takeaway for the OP is that there are workarounds that will give him some freedom to use a derailleur that is not 100% within take up spec.

FWIW - eons ago I set up my road bike for mountainous touring by adding a "bailout" granny, without changing the RD which was already near capacity. The granny was only usable with the largest 2 rear sprockets, but who cared since it was strictly for limited situations anyway.

grumpus

The chain might just refuse to climb onto the larger sprocket, and rattle a lot. It might start winding on then jam as the chain runs out of length. It might bend/break the RD cage, tension roller, teeth or chain. It might break the derailleur hanger, chucking the derailleur into the spokes, collapsing the wheel, breaking the chain stay and sending razor sharp shards of carbon fibre into your groin.

anga

Interesting points. Will take me some time and effort to absorb.

Advent not available here.

Can I remove the smallest cogs, 11t, 12t & 13t and start with 14t or 15t?
Is the RD limit on the maximum size of smallest cog binding?

squirtdad

need a lot more details....
like what size of triple
what shifters, index or friction

there are 2 or 3 (depending on you count them) measures of capacity for rear deraillers

1) Chain wrap or capacity which is calculated by as difference between largest and smallest chain rings + difference between largest and smallest rear cog
2) minimum and maxium rear cogs
3) newer rear deraillers also specify max difference between largest and smallest chain rings

as an example the deore m591 9 speed has a max wrap/capacity of 45 but more critical has a max rear cog of 34 with is a long way from 40

that is pretty much high end of anything I have seen shimano wise

so you are most likely going to have to look at a different configuration

FBinNY 

There's no point in removing the smaller cassette sprockets, since options are limited for the 1st position which has a built on spacer.

In any case, you'd also need to replace half the cassette to end up with a logical progression.

However, if you're willing to have a high gear about 25% lower, you should consider smaller chainrings. That will yield the gearing you want with decent spacing, without needing nearly as much chain take up.

Whatever you do, do it logically, and make sure the RD can handle a 40t (or whatever) sprocket.

70sSanO

Without knowing the crank and chainrings, it is tough to make recommendations.

My brother built a road triple with a older XT crank and 22-34-44 chainrings. He used an 11-32 cassette.

The 44-11 gave him a 4:1 ratio and the 22-32 gave him .69:1. You do have to figure out the FD shifting if you are using drop bars.

I have a couple of mtb’s with a 13-40 8 speed using a Wolftooth RoadLink. With 24-34 chainrings the low is .6:1 which is about the lowest I think is practical to ride without falling over due to too slow a speed. They are strictly for trail riding so top end on flat roads is not needed.

You can run a 13t or 14t 1st position but they are tougher to find. I have a bike with an 8 speed 14-36. At times it is a bit light on top speed; about 25mph. I bought a 14t 1st position cog, for a junior cassette, and built the cassette with gaps I want.

John

anga

Time for specifics.

Crankset is installed.
FC-M2000, 22 x 30 x 40T.
https://bike.shimano.com/en-EU/produ.../FC-M2000.html

Bought FD, FD-M2000 & corresponding front shifter.
https://bike.shimano.com/en-EU/produ...M2000-TS3.html

Current cassette is 7-speed, 12 - 28T.
Have 8-speed rear shifter.

Need to buy cassettes, RD for new setup.

First solution
The cassette is CS-HG400-8, 8-speed, 11-13-15-18-22-27-33-40T.
https://bike.shimano.com/en-EU/produ...S-HG400-8.html

RD is Shimano RD-M3020-8
https://bike.shimano.com/en-EU/produ...D-M3020-8.html

Initial idea is to buy another cassette, 7, 8 or 9 speed, with 21, 24, 28, 32 & 36 teeth cogs and combine with CS-HG400-8, 11-13-15-18-22-27-33-40T and get​15-18-21-24-28-32-36-40.
This is the only 8-speed & 40T solution that is available in India.

Second solution
If the smallest cog of 14 or 15T is impossible.Simpler alternative seems to be to drop the 40T cog and be satisfied with 36T.An 8-speed cassette with 36T is not available here.

I can go for a 9-speed cassette CS-HG400-9, 9-SPEED, 12-14-16-18-21-24-28-32-36(BH).
With 8-speed spacers in above cassette between cogs from 14T and 36T (and not use 12T, apparently the smallest cog cannot be removed), can I use 8-speed shifter and 7-speed derailleur?

Hondo6

Best I can tell from its specifications, the RD you have should be a decent choice. And with a 45T capacity, it might even work as-is with the 11-40 CS-400-8 (with your existing crankset that would require 47T capacity, but Shimano has generally seemed to be conservative in their RD capacity ratings).

Unfortunately, I'm not sure the custom gearing you want to do is even theoretically possible any more. And even if it is, you might want to think twice - because it will degrade shifting performance.

Disclaimer: I don't have a CS-400-8 11-40 in my hands, so what I'm about to say is based on photos.

Shimano (and other manufacturers) now mount many rear sprockets on carriers vice having the sprockets extend all the way to the freehub and using individual spacers between them. This latter - and older - type of cassette could be disassembled, sometimes with difficulty. But that's not as easy (or maybe impossible; I've never tried) with carrier-mounted sprockets.

With carrier-mounted sprockets, the sprockets themselves generally don't extend to the freehub; they are mounted to the carrier and have no splines. The carriers are splined and fit on the freehub instead. Photos indicate that this is indeed the case for the 11-40 CS-400-8 cassette. My guess is that this was likely done to save weight, particularly as Shimano says all 8 sprockets on the 11-40 CS-HG400-8 are steel.

Sprockets on carriers are generally not designed to be removed; I'm not really sure if they can be without significant damage to the carrier or the sprocket. And depending on how they're spaced (likely with mounting bosses on the carrier serving as spacers), the carrier may not readily accommodate different sized sprockets even if the existing sprockets can be removed without damaging either the carrier or sprocket.

Based on this photo, at least the 5 largest sprockets on the 11-40 HG-400-8 appear to be mounted to a carrier. It's possible the 7 largest sprockets are attached to the carrier; some smaller sprockets overlap enough that I can't tell from the photo whether they extend to the freehub or not.


I would strongly advise against attempting to remove any sprockets that are carrier-mounted from the carrier. Sprockets that extend all the way to the freehub may be individually replaceable with the proper spacers, provided you can remove them from the existing cassette without damage.

Unfortunately, Hyperglide cassettes are matched sets with the shifting aides on adjacent sprockets (shaped teeth and ramps/gates built into the sprockets themselves) aligned for best shifting. Changing sprockets will alter that alignment for both upshifts to and downshifts from the changed sprocket, which will in turn degrade shifting.

A second problem is that you should not simply discard the smallest sprocket on a Shimano Hyperglide cassette. The smallest sprocket on a Shimano Hyperglide cassette has ridges that mate with corresponding ridges on the lockring to lock the cassette in place, and also has an integral spacer. This photo shows the design (12T 8-sp outer sprocket):



For comparison, here's a 13T 8-sp non-outer sprocket with integrated spacer Note the absence of ridges to engage a lockring.



In order to change the number of teeth on that outer sprocket, you need to replace the existing sprocket with one similarly designed - e.g., which also has the ridges and integral spacer. If the original outer sprocket is an 11T, you'll also very likely need a new lockring; 11T lockrings reputedly don't work with 12T and larger outer sprockets.

I personally would not attempt to ride with an outer sprocket that did not have the required lockring ridges. My working assumption is that Shimano put those ridges there for a good reason, and that if they're absent the cassette may not lock in place properly and work loose during use. A cassette working loose under load is not a good thing.

From the document available at this link, it appears that only the outermost sprocket on the 11-40 CS-400-8 is easily replaceable. If you can find a 12T outer sprocket and lockring, that might be an option - and it would reduce your required RD capacity to 46T.

11T and 12T outer sprockets appear to be reasonably available for Shimano-type cassettes. As noted by 70sSanO above, 13T and larger outer sprockets exist - I've seen specialty cassettes with a large as a 16T smallest cog offered for sale. But they're difficult to find individually.

My suggestion would be to simply try the 11-40 CS-400-8 as it comes from the factory and, if necessary, find a smaller larger outer sprocket and lockring to replace the existing 11T outer sprocket and lockring. But it's your bike; do what you want.

squirtdad

by the spec the 11-40 and 40/22 are close and will likely work. reccommend just using that set up and do not attempt to play around with changing cogs on the cassette

RD spec show 45 max chain warp, 40 max rear cog and 20 tooth crankset differrence

you set up would be 47 wrap, 40 max and 18 should work smoothly

70sSanO

If you "can't" go to 9 speed shifters, which is the best solution, this is your solution. I think the HG400 cogs are full length and not on a carrier/spider but you will need to confirm. If you can get one of these...

https://www.ebay.com/itm/33262671841...Bk9SR-qr1O6OYQ

... you can make it work. You'll have to sand down the 3 tabs on the back to get the correct cog-to-cog spacing, but despite on having just those tabs, it has worked well for me. It doesn't matter that it is for an 11 speed cassette. I think it would be better to find a junior 14t cog in 9 speed, but with compact/subcompact cranks those days are long gone.

Unless you are using an old UG/HG threaded freewheel body, you will have a problem using any non 1st position cog that doesn't have an integrated spacer due to the relief on the end of the freehub body.

John

Edit added: The Shimano PN for the 14t cog is Y1Y914100.
https://si.shimano.com/ko/pdfs/ev/CS...R8000-4257.pdf

Hondo6

Shimano EVs show all current CS-HG400-9's have at least 5 carrier-mounted sprockets, 70sSanO.

https://si.shimano.com/en/manual/sea...del=CS-HG400-9

The OP's interested in using the 11-36 version. Per the EV ending in 3680, that cassette's config is 11T (outer, w/built-in spacer); 13T (removable, w/built-in spacer), and carrier-mounted 15-17-20-23-26-30-36T sprockets.

Problem is, I don't see any good way to respace the carrier-mounted cogs to 8-speed spacing. So the OP would have a shifter/cog-spacing mismatch as well as a cassette a few mm too short. There might be work-arounds that would allow the OP to use his existing shifter, but I don't know what those would be or if the OP wants to try that or not.

I think either your suggestion of (a) getting a 9-speed rear shifter and using the 11-36 CS-HG400-9 cassette as-is, or (b) trying the 11-40 CS-HG400-8 as-is with his existing 8-speed rear shifter and existing/intended derailleurs would be the OPs best courses of action. But it's his bike and his call.

70sSanO

Not the one I'm holding in my hand.

The EV shows the riveted block of full cogs.

John

Iride01 

Do you really think you need that low a gear ratio or gear-inches? 22f/40r and you'll probably be able to pull stumps out of the ground. Well that's a bit of exaggeration, but still that's a super low gear.

Hondo6

@70sSanO: If you don't mind, what's the date on that EV? Is it Apr 2017? That's the latest one Shimano seems to have on-line. (They don't seem to have one on-line for the CS-HG400-8 that I can find.)

If so, I'll defer to your expertise. I was interpreting those diagrams as showing carrier-mounted cogs, but I could well be wrong. (I couldn't find a decent rear or profile view photo of that particular cassette, which might have been definitive.)

In that case, your solution would indeed work for the OP after he'd disassembled and respaced the riveted sprockets.

70sSanO

I just used the link in your post.

I didn’t break apart cassettes until an old 7 speed trigger shifter broke a while back and I replaced it with an 8 speed shifter and respaced the cassette.

I would never recommend this for the vast majority of people; and the riveted cogs are better for not grooving a freehub body. On a UG/HG body I have run a non-first position cog with an outer shim, but you do have to make sure the lockring is well torqued.

Admittedly, it has become a bit of a game for me; building cassettes with the gaps I want. It reminds me of the old cog boards for freewheels. While I sometimes miss a 12t or 13t on downhills, my cogset (cassette) becomes a bit better suited with every passing year.

John

Hondo6

Well, I guess I was wrong. Isn't the first time in my life, and certainly won't be the last - maybe not even today. Thanks for setting me straight.

OP: The man's advice is sound if you decide to go with the 9-speed cassette and respace it, provided you can get the spacers and order (and modify) the cog he suggests.

I guess it's now time to see how crow tastes with Tabasco or Cholula . . . .