Optimal Chainlength - It's A New Day
Posted: Wed Jun 27, 2018 6:04 pm
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?
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...
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)....
Next... Big chainring/Largest cog... also just fine...
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...
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)...
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?...
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...
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...
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.
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?
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...
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)....
Next... Big chainring/Largest cog... also just fine...
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...
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)...
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?...
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...
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...
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.