Optimal Chainlength - It's A New Day

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Calnago
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by Calnago

Several weeks ago I noticed a topic about chainlength. Well, times have changed with new derailleur designs, larger cassettes, etc. In the past, there were bascially two methods to determine the chainlength... the Shimano method (using big chainring/biggest cog with chain not run through the derailleur), and the Campy method (using smallest chainring/smallest cog with chain run through the derailleur). Being a Campy guy, I used the small/small method and regardless of the cassette size being used, as long as everything was compatible, this would work for any combination of cassettes from 11/23 - 11/29 (in the case of current 11sp), with a slight adjustment of the H-Screw when changing cassettes. And if you were to use this method with Shimano derailleurs prior to the 9100 series, it seemed to work the same way. Six of one, half a dozen of another.

But, since the introduction of Shimano 9100 type rear derailleurs, and the new Campy 12sp stuff, a bit of a rethink is in order. In a nutshell, if you are using the newest Shimano road derailleurs, then absolutely (as opposed to using either method) use the Big chainring/Biggest cog method. Failing to do so may result in a chainlength making an optimal setup with respect to shifting performance next to impossible to achieve. And for the newest Campy 12sp stuff... well, it's really simple now... for chainstay lengths from 405mm to 415mm (which cover the vast majority of road bikes), use 110 links, regardless of cassette and regardless of which chainring combo you are using, be it standard (39/53), mid (36/52) or compact (34/50). If your chainlength is longer than 415mm, then go to 112mm. Pretty simple. I'll discuss that a bit more later.

So, let's look at the Shimano stuff first to understand why I'm even writing about such a seemingly straightforward thing as chainlength. Well, first of all, it's not that straightforward anymore. Let's start with an actual real example... here's a pic of a drivetrain with DuraAce 9150, standard chainrings (39/53) and an 11/25 cassette... chain is on the small ring up front and 3rd rear cog (counting up from the smallest), as DuraAce locks you out of the smallest two cogs by default. What do you think... too long?... too short?... optimal?... or don't know?
Image
If you think it's too long, you probably wouldn't be alone, especially when seeing how slack it is and it's not even on the smallest cog. Fact is, this is the optimal chainlength for this setup. The B-Screw on the new derailleurs can take up a lot of slack, yet the system as a whole is very sensitive to having the proper chainlength to start with. In other words... if your chain is a bit too long to start with, it is quite likely that you'll be able to get the slack out of it by adjusting the B-screw, but it is unlikely you will have the upper pulley close enough to the cogs to provide optimal shifting. Will it work?... probably.... but if you want crisp and fast shifting at it's best, you may be missing the boat. Remember... the closer you can keep the upper pulley to the cogs across the entire cassette's range, the better and crisper the shifting will be.

Ok... so here's the same setup above with the B-screw turned in a smidge... it was easy to take up the slack and didn't take much of an adjustment at all... note that I was able to take all the slack out without the pulleys moving appreciably farther away from the cassette. If the chain was a bit too long... I could have taken the slack out, but at the expense of moving the pulleys farther away during the process...
Image
Clearly better, right... now let's take a quick look at the extreme combos with this setup...
First... Small chainring/Largest cog... when looking at these pics, take note how close the upper pulley is to the cogs and the good "wrap" it achieves towards the front, particularly in the smaller cogs (more on that later)....
Image

Next... Big chainring/Largest cog... also just fine...
Image

All good so far, (I'm omitting a pic of the Big chainring/smallest cog as it is perfectly ok and not really one of the extreme combos you have to worry too much about, so doesn't provide much interest in this context).

Now, according to the Shimano instructions, the chain overlapped in such a way that they give you the option of adding one link or three links, (if you think the drive train might "wander"). By "wandering" they mean flexing or pivoting enough that the chain couldn't accommodate the change (think of a suspended mtn bike with pivoting chainstays). However, I would strongly suggest to NEVER just add the one link. It's simply too tight. I'll get to the overlapping thing shortly but first I want to show you how this bike was brought to me. It was set up with a technically correct (according to the Shimano docs) length (1 added link), and here's how it looked. I just used my bent spoke to simulate the length it was at when brought to me, owner was oblivious to any thought that the chain may be on the short side...
Image
Ouch! It hurts so bad to see a chain that tight, and set up by a very good mechanic no less. Like I said, it's easy to get wrong, or if not tehnically wrong (it still fits after all), then at least functionally so tight that it hurts. And forget the small/small method when dealing with current Shimano derailleurs. It worked in the past, but the past is the past, and using that method with the current stuff could very well lead to a less than great setup. Plus, with Di2 you're typically locked out of getting the chain in the small/small combo anyway, so setting the chain length using that method becomes more problematic. Also, forget any "calculators" that don't take into account the various changes in derailleurs, like cage length, pulley sizes, etc. In the pic above, which is on a Pinarello K8-S with flexy stays and a bit of suspension, "wandering" (as shimano calls it) of the chainstays could be the straw that breaks things apart here.


So, where do you cut the chain then... it can be a bit confusing at first. Looking at the pics in the Shimano tech docs, it seems like it should be such a simple thing. But considering the chains now come with a Quick-Link, instead of the separate rivet, you have to take that into account as well when determining where to cut the chain.

Let's take a look below at a couple of chain overlaps. Assume that the chain is wrapped around the big ring and largest cog and not run through the derailleur. It is pulled as tight as you can get it and overlaps as in the examples below. Also asuume that you'll be cutting from the end coming from the rear derailleur side of things...

The chain below does not use a quick link (that example is next). Where would you cut this chain assuming no quick link?... (use the reference numbers I just wrote above each pin)...
Image


I would break the chain at Reference Point #4, which adds 3 links to the chain. The Shimano docs actually say that adding 1 or 3 links is ok, but as I showed earlier, if you were to only add one link and break the chain at Ref Point #2, you are going to end up with a very very tight chain putting a whole lot of strain on the system. Don't do that.


Sticking with the case where there is no quick link being used, here's another example... where would you break the chain?...
Image
Break the above example at Ref Point #4... that will add two links to the chain and it will be fine. The point to all this is, that depending on how the chain overlaps (whether the outer links match up or not), you should add either 2 or 3 links to the chain, and never just add one, even though that's an option in the Shimano docs on chain length.


Ok... now since new chains are supplied with the quick link... let's turn to that example...
Where would you break this chain...
Image
Break it at Ref Point #2. When you add the quick link that will be adding 2 links to the chain, which is good. You can always insert the quick link in the end while you figure it out if that makes it easier for you.

And the last example... different overlap where outer plates don't match up...
Image
Break this one at Ref Point #4 which, when the quick link is added, will add three links to the chain. Breaking it at Ref Point #2 will produce a chain that adds one link, and while it will fit, is simply too short and will produce the result that I showed earlier in the pic of the bike with the chain mounted, but it's just too short.

Now, while using Shimano's method for chainsizing really does produce the optimal length for setting up the new derailleurs for the best shifting possible, you could also find yourself in a situation when changing to a larger cassette for example, that the chain may not be quite long enough. So what do you do, do you cut it extra long to accommodate for that? I wouldn't, because then it will require such an ajustment to the B-screw that it will pull the upper pulley back from the cogs resulting in shifting that isn't quite as good as it could be. I think if I were in that situation of swapping wheels with cassettes of large size discrepencies, I'd just buck up for a couple chains that match those combos, since with the quick link that is supplied it's so easy to just change them. I'm going to have more to say about that in my next technical post, which will kind of be a followup from this one, and be a continuance of the whole direct mount hanger saga and the potential for difficult wheel removal.
I will just add to the thread that already contains most of the preamble for that... Here's the link to the post where I left off in that thread... https://weightweenies.starbike.com/foru ... #p1392783
When I continue that I'll talk more about the whole DM Hanger issues some more, and look at what Team Sky has done... the stuff that doesn't get mentioned in the Shimano docs.
Ok... so that's it for Shimano chain lengths and the new derailleurs. Now what about Campy....

Campagnolo Chain length...
Really quite simple, and probably the most used method around, regardless of whether it was old shimano or Campy, at least up to 11 speed... chain on small ring, small cog, run through the derialleur, then cut it at its longest point so that there is still some tension on the rear derailleur while making sure that the chain still clears the pulley assembly in that position with no rubbing. This will give you the longest chain possible and I was able to get the gap properly adjusted for any cassette combo from 11/23 through 11/29.

But what about the new Campy 12sp stuff... Well, this is the simplest of all now... here's the guideline:
- For chainstay lengths of 405-415mm... use 110 links. This is regardless of cassette size (within compatibility guidelines of course), or chainring combos, be it 34/50, 36/52, or 39/53. Excellent! So easy although I've yet to test it out for real yet. But as it is with 11sp stuff now, on my bikes if I want to switch out cranks from say, a standard 39/53 to a mid compact (36/52), I would need to go from a 110 link chain to a 108 link chain, or run with some slack when things start getting crossed. So, if this new guideline for 12sp works just fine, that means I can easily switch cranks and cassettes and use any combos I want without messing with chain lenghts. Me likey.
- For chainstay lengths greater than 415mm... the guideline is simply to got to 112 links. Pretty easy. Although I'm not sure at what chainstay length you would require more, so some experimentation may be in order there.


I guess the takeaway from all this is that determining the best chainlength isn't quite as simple as it used to be, but with the current crop of derailleurs, achieving the best shifting performance relies on it. Park Tools has some very good videos that will also get you there, and I'd suggest looking at those. Interestingly, none of those videos will ever get you to the "add just one link" option, which is good. Avoid it like the plague.

Whew... was wondering if I'd ever get around to posting this, but I took the pics, so couldn't really just waste 'em.
Last edited by Calnago on Wed Jun 27, 2018 6:04 pm, edited 5 times in total.
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by Weenie


Robbyville
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by Robbyville

Awesome post, and just a the right time, thanks so much! With the new crop of chains (specifically for me the Dura Ace 9100), still replace every 3000 miles or so?

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Calnago
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by Calnago

Mileage is such a vague guideline when talking about chain replacment intervals. Varies with so many things. I use some measuring guidelines as well as just by feel when shifting starts to degrade.
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Hexsense
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by Hexsense

Whoa, i almost assume to just use Campagnolo Chain length's method on the 8050 set-up that i'll build soon already.
Thanks for reminding me to consider adding more links.

BTW: i didn't buy Ultegra RD yet, but for using 11-28 and 11-30 (never use 11-32 and 11-25).
Should i select Short cage (which is for 11-25 to 11-30) or Mid cage (which is for 11-28 to 11-32) ?

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Calnago
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by Calnago

@Hexsense, if you’’re never going to use a cassette smaller than 28 largest cog, then probably the midcage would be best, if it goes to 32, just to maybe give you the option down the road. For the 34 tooth cassette, you have to go with the Ultegra GS cage. I’ll go into some more details on that in my next related post, which will be more interesting. But you need the chainlength right to begin with.
[edit]: I’ve just reread your question and I guess you could go either way. If you think you might ever use smaller cassettes, then I’d probably stick with the short cage and vice versus if you think you’ll use the 32 at some point. Sort of a tossup I guess.

When 9100/50 first came out, a shopowner friend brought over a bike for me to have a look at. It was the first 9150 stuff I had seen and I immediately went to the rear derailleur to play around a bit. Right away almost, I ascertained that the chain was too long and showed him how slack I could make it with hardly any turn of the b-screw. I did him a “favor” and we shortened it right there. But I’m pretty sure In hindsight that the owner of that bike is riding with a chain that is too short at this point, if it hasn’t been changed since. I will track him down, buy him a new chain and install it for him. Last winter I really went to town in figuring out all the nuances of the new Shimano derailleurs, especially as to why the rear wheel removal is such a pain in the ass sometimes. Learned a lot and when I saw the thread on chainlength maybe a couple of months ago I almost started posting to it. But then I figured starting a new thread (for the new day) would be a better idea. Hope it helps and saves a few people from making the same mistake I did. By the way, that chain in the photo I showed above where it’s too short was installed by a mechanic I have the utmost respect for, but like me, was probably so used to just using the small/small method that no further thought was given to it. It may or may not work, but it depends on a number of things, one being exactly where that B-Screw is positioned when you start. Things ain’t like they used to be.
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Hexsense
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by Hexsense

There is no reason to select 11-25 or 11-26 for me, Sram 11-28 is just plain better because they are the same from 11 to 19 and only different near the end where i don't mind bigger tooth jump.

11-12-13-14-15-16-17-19-21-23-25 (or 26)
vs
11-12-13-14-15-16-17-19-22-25-28

Yeah, it work either way. But with different body and cage length of two version, maybe one will make upper pulley more closer to the cassette throughout the whole range? I don't know. Maybe i'll just buy whatever come cheapest when i buy.

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Miller
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by Miller

What an obsessive you are, Calnago, and you bring value to WW with that.

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Calnago
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by Calnago

@Hexaense: Yes, I’m with ya.
@Miller: yes to that too, I need to know the nuances of how things work. If you understand that, it makes fixing stuff and troubleshooting a breeze, rather than just a try this or try that approach and hope for the best.

And if I owned a shop, and the mechanics couldn't immediately tell me where to break those chains in the photos above, then I'd tell them to study up until they can. Ha.

And looking back at my initial post (on Tapatalk now) I see that at least one photo isn’t showing up (in Tapatalk) but it’s fine on my laptop. It’s happened before but I’m not sure why. Later I will try to reinsert the missing photo again maybe to seen if that reestablishes the photo in Tapatalk.
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2lo8
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by 2lo8

I missed what's wrong with small/small, especailly if you're not running Di2. Trying to figure out how chain tension matters when the jockey cage has 0 offset.
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Calnago
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by Calnago

Using small/small with the new shimano derialleurs, mechanical or Di2, can fairly easily end up leaving with you a too short chain, depending on where the B-screw is set when you start. For example, screw the B-Screw all the way out, or a couple of turns at least. Then determine where you'd break the chain under that scenario using small/small. Now, turn the B-screw a few turns the other way (tightening it), and then determine where you might break the chain. You will quickly see how much that can vary. The B-Screw on the new shimano derailleurs has a tremendous effect here, and doesn't take much adjusting. And as I mentioned, with Di2 you're going to be locked out of positioning the chain on small/small anyway for the most part. It's just a change in habits I guess. For shimano setups with the newer derailleurs, for me it's the big/big method (no run through the derailleur) with the guidelines above. It will be correct every time, and the B-screw will not come into play in its determination, as it might if the chain is run through the derailleur. So, if you can't seem to get the final adjustment of your upper pulley very close to the cogs, this may be the culprit. Using small/small may very well end up with the same length as the other method, and most certainly prior to the new derailleurs I would say it always did and was my preferred method of ensuring I had the longest chain possible, regardless of whether it was Campy or Shimano. But things are a bit differnt now. Using small/small is just not as reliable a method anymore when faced with the new Shimano derailleurs. I'm anxious to see how this all plays out with the newest 12sp stuff from Campy.

If the chain isn't the right length, there were cases in my testing where I was not able to adjust the derialleur as optimally as I could if it were the "correct" length.
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Hexsense
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by Hexsense

maybe i'll try to adjust B-screw without chain first. Just set to where top pulley is closest to the cassette.
And then do a small+small (through derailleur) to set-up chain length (or small front+second smallest back). That would give it longest possible chain with the combo, instead of set chain length first then adjust B-screw later which can change effective chain length.

Good thing about the new generation Shimano RD is that, like Sram road RD without clutch, top pulley do not move when the cage bend forward or backward as it has 0 offset from rotation point. Which i find it nice and more consistence than when top pulley change their position with cage tension.

2lo8
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by 2lo8

I think I see what you're trying to say now. It would be nice to see if there's a way to size a chain for maximum big-big even if you don't have the big cassette on while sizing the chain.
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Calnago
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by Calnago

I’ve experimented with all those things. The B-screw plays with the chain in play. Backing it out all the way will allow the upper pulley closest to the cassette. But if you try to run it through the pulleys then cut it you will find yourself with a messed up length. But I encourage you to experiment for yourself to get a feel for how it all really interacts together.

I also wondered what would happen if I made the chain as long as possible so that I could potentially just throw in a wheel with a bigger cassette. And you can do that. But not without having to turn in the B-Screw further to take up slack. And in so doing it will pull the pulley farther away from cassette than if you were using the optimal chain length for that cassette. It will still shift and all, and probably very well, but it won’t be as crisp as if the whole thing were closer. Remember, the best shifting will occur when you have the upper pulley and chain as close to the cogs as possible without jamming. I’ve got some interesting stuff to present in my “next installment”.
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kode54
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by kode54

interesting that you've just posted this. i've had an issue where I just put a new chain on and it started skipping on the cassette. the B screw was too loose, so I tightened it a bit and it fixed it. my Di2 won't let me go small chainring to small cog...it'll be 3 up from the smallest, so I'll never exhibit the same loose chain that you show before tightening up the B screw. seems a bit more sensitive to that.
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by Weenie


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Calnago
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by Calnago

That loose chain that I pictured is in fact Di2, and it is on the 3rd cog from the smallest. I just loosened the B-screw to highlight the fact that depending on where the b-screw is set initially, it could be deceptive as to where exactly to cut the chain if you were trying to use the small/small method. That “loose”’ chain I depicted is actually the ideal length for that setup, it just needs the final b-screw adjustment.
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