# How do you determine chain length the Shimano way?



## baker921 (Jul 20, 2007)

I'm building my first bike with a double (compact) crankset and am trying to do it by the book. I am familiar with the "big to big + 2 (half) links" method but am trying to follow Shimano's instructions and align hub, guide and tension pulley centres at right angles to the ground.
So I have the bike in the stand, wheels on level ground, right hand grasping the well lubed ends of the new chain wrestling against the tight springs of the new RD. I am either bent double or lying on the ground left hand attempting to manipulate plumbline, set square and spirit level. Shimano and Zinn are both silent on *how* to achieve this feat.
So what do you Pros do? I'm reluctant to try clamping the chain together. Is this a 2,3,4 man job? Do you ignore Shimano and use the other method? Is there a "conversion factor" so I can use the other method +or- a half link. Please tell me the secret.:mad2:


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## rx-79g (Sep 14, 2010)

As a human being, the visual centers in your brain are very good at detecting whether something is vertical or horizontal. God made you that way to hang pictures for the wife. So put down the all the measuring crap and LOOK at the pulleys. There are only going to be two chain lengths that are even close to vertical. Pick one of them and you'll be fine.

When actually doing it, grab the two chain ends, overlap them, hold the length to the cut and allow the tension to go back to zero. Cut the chain where you're holding it, take the chain off the chainrings to get some slack, then connect it.


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## danl1 (Jul 23, 2005)

rx-79g said:


> As a human being, the visual centers in your brain are very good at detecting whether something is vertical or horizontal. God made you that way to hang pictures for the wife. So put down the all the measuring crap and LOOK at the pulleys. There are only going to be two chain lengths that are even close to vertical. Pick one of them and you'll be fine.
> 
> When actually doing it, grab the two chain ends, overlap them, hold the length to the cut and allow the tension to go back to zero. Cut the chain where you're holding it, take the chain off the chainrings to get some slack, then connect it.


What he said. Once you get it in the right gear and the chain all wrapped, actually picking the right link is pretty easy. 

Another tip: Make a chain hook. Find a piece of reasonably fine wire (a cheap hanger from the dry cleaners will do nicely) and cut off a piece ~4" long. Bend a hook in one end, and hook it into a length of chain. Measure down so that you are in line with a link 3 or so inches down, and bend another hook at that point. It doesn't have to be dead perfect. 

You can use that to help hold the loose ends of the chain together, making it easier to take a step back, take a breath, and look at what you are doing. Once you settle on a length, having the hook holding the chain will make it easy to line up the right place to break the chain, and much easier to join it back together. The derraileur tension will help keep things from flopping around while you're getting the pins and chain tool all lined up, but you won't need to fight it at your join point.

It's not a new idea - many chain tools and certain minitools include one. It's just that a lot of folks don't know what to make of that little loop of wire.


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## FBinNY (Jan 24, 2009)

+3, it doesn't call for any degree of precision, since you're locked into increments of 1" of chain. Use the length that yields what appears to be the nearest to vertical.

BTW- I don't know when people started to talk about half links, or links being equal to an inch, but doing so leads to confusion. A link in a bicycle chain has always meant 1/2" of length, or 1 pitch, ie a 110 link chain is 55" long, (read the box when you buy one) 

There are inner links and outer links, and for SS use there are the inner/outer links that make possible chains with an odd number of links.


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## danl1 (Jul 23, 2005)

FBinNY said:


> BTW- I don't know when people started to talk about half links, or links being equal to an inch, but doing so leads to confusion. A link in a bicycle chain has always meant 1/2" of length, or 1 pitch, ie a 110 link chain is 55" long, (read the box when you buy one)
> 
> There are inner links and outer links, and for SS use there are the inner/outer links that make possible chains with an odd number of links.


Although, if you look in any bike catalog or industrial chain supplier, those inner/outer links are referred to as 'half links,' and if you seek a chain made entirely of those links, it's called a half-link chain. So even the manufacturers are inconsistent.

IMO, you kinda give it away yourself, when you mention "1 pitch." Why would there be two different terms (pitch and link) for the same thing?

It is an oddity... 1/2" makes the most visual sense as one link, but on the other hand, it doesn't make much sense to not be able to take one link out of a length of chain. If you ask me, that's the confusing part. I've seen all to many people break a chain to the 'perfect' length, only to be frustrated when they then realize that they've just created two inner or outer ends to try to join, and end up an inch shorter than they ought to have.

As for when, chains used to be made up entirely of what are today called 'half-links.' They stopped doing that as the mainstream method of transmission chain making in the 1890's, when they realized that the curved plates stretched too much, something quite impossible with the modern inner-outer chain. 

Where've you been?  

Since then, both definitions have been used, depending on the context of the discussion. The Knower of All Things Bicycle (the late, great Sheldon Brown) usually used the 1" nomenclature when talking about length, and the 1/2" when talking about chain / cog pitch. Who are we mere mortals to argue?

http://sheldonbrown.com/derailer-adjustment.html#chain

BTW, I'm not really arguing, and certainly not saying you're wrong. More just noting the irony that without language, we wouldn't have much to argue about.


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## FBinNY (Jan 24, 2009)

danl1 said:


> Although, if you look in any bike catalog or industrial chain supplier, those inner/outer links are referred to as 'half links,' and if you seek a chain made entirely of those links, it's called a half-link chain. So even the manufacturers are inconsistent.
> .


I don't know the etymology of the term _half link, but it might not because it's half a link, but because it was half inner and half outer, sort of a half breed link. 

So here's the million dollar question. If you made up a chain a chain using 110 half links, how many links long would you say it was.

I really don't care what we call a link, just so we can all get on the same page. It'll reduce confusion when we say things like big/big + 2 (or it one or it 4?) links._


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## Kerry Irons (Feb 25, 2002)

*Who cares?*



baker921 said:


> I'm building my first bike with a double (compact) crankset and am trying to do it by the book. I am familiar with the "big to big + 2 (half) links" method but am trying to follow Shimano's instructions and align hub, guide and tension pulley centres at right angles to the ground.
> So I have the bike in the stand, wheels on level ground, right hand grasping the well lubed ends of the new chain wrestling against the tight springs of the new RD. I am either bent double or lying on the ground left hand attempting to manipulate plumbline, set square and spirit level. Shimano and Zinn are both silent on *how* to achieve this feat.
> So what do you Pros do? I'm reluctant to try clamping the chain together. Is this a 2,3,4 man job? Do you ignore Shimano and use the other method? Is there a "conversion factor" so I can use the other method +or- a half link. Please tell me the secret.


You are WAY over thinking this. Put the chain in the small-small combination and then take out enough links so that the rear derailleur starts to engage. That method works the best. As others have said, since you'll be removing an inch at a time, if you want to use the overly-complicated Shimano approach you can easily see which lenght leaves your derailleur most straight up and down.


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## pacificaslim (Sep 10, 2008)

I just calculate it. 

Length of chain in inches equals the sum of:
twice the chainstay length (round to nearest .125") 
plus one forth the number of teeth on the largest chainring 
plus one forth the number of teeth on the largest cog
plus one

Example, my Ritchey cross bike:

2x16.75 + 50/4 + 26/4 + 1 = 53.5 inches, round up to 54" or 108 lengths.


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## cxwrench (Nov 9, 2004)

pacificaslim said:


> I just calculate it.
> 
> Length of chain in inches equals the sum of:
> twice the chainstay length (round to nearest .125")
> ...


while it is interesting that you can figure it out like that...it's wayyyyyy too much thinking. i do the same thing as Kerry...small/small, pull just tight enough to pull the cage down enough to clear the chain. works every time.


except for my mtb double w/ a 36


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## rx-79g (Sep 14, 2010)

Kerry Irons said:


> You are WAY over thinking this. Put the chain in the small-small combination and then take out enough links so that the rear derailleur starts to engage. That method works the best. As others have said, since you'll be removing an inch at a time, if you want to use the overly-complicated Shimano approach you can easily see which lenght leaves your derailleur most straight up and down.


I don't see how this is any easier to do. In both cases you put the chain on and visually pull it to a certain tension. 

The difference is that one method is the one specified by the manufacturer which takes cage length into account, and your method is happens to work but doesn't provide the optimal length, or even a guaranteed safe one like the big/big method does. It is also adversely affected by B-tension preload.


The calculation method of Pacificalism is far worse, though. It fails to account for hanger length and location, cage length or pulley size. It offers the opportunity to mismeasure, miscalculate or mis-count the links.

It's so funny how against doing things by the book some people are, even when the Shimano method is the fastest and most accurate method for these derailleurs.


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## danl1 (Jul 23, 2005)

FBinNY said:


> I don't know the etymology of the term _half link, but it might not because it's half a link, but because it was half inner and half outer, sort of a half breed link.
> 
> So here's the million dollar question. If you made up a chain a chain using 110 half links, how many links long would you say it was.
> 
> I really don't care what we call a link, just so we can all get on the same page. It'll reduce confusion when we say things like big/big + 2 (or it one or it 4?) links._


_

Of course, just about the time we get it settled, some bozo will invent quick links and throw it all in the hopper. 

We could use length units to describe length: Big-big plus an inch. Or non-equivocal units: Big-big plus two rivets. 


FWIW, I think big big plus one inch is shorter than it should be. It usually works, but it's ass-ugly, and I think an extra inch shifts better. +1 was fine when full-cross was a verboten, noisy mess, but with today's flexible chains and compact drivetrains, +2 inches works better IMO._


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## FBinNY (Jan 24, 2009)

Anyway, back to the OP original question there are three important chain lengths.

1- *minimum length*, as determined by the big/big + 2 (1") method. There's no fudge room here. It's a true minimum length since otherwise the consequences of accidentally shifting into this combination are too serious.

2- *maximum length*, as determined by the small/small & RD cage off the dead stop method. There's a bit of fudge possible here since one doesn't tend to ride crossed over anyway, so an extra inch or so beyond the max is acceptable in a pinch.

If the Maximum is less than the minimum you need a longer cage RD. If there's a range available between max. and min. anything in between is OK, but that brings up the third length which is the *best length* within that range. 

On RDs where the cage rotates around the upper pulley chain length doesn't matter since it doesn't change pulley to sprocket distance. But on RDs where the cage pivots between the pulleys optimizing chain length improves performance since the jockey wheel rises and falls as the cage rotates. The objective is to find the length which brings the pulley up closer on smaller sprockets, and down to clear larger sprockets. This is easy on 1x? systems, but trickier on double and triple systems.

Finding the right chain length (where there's a choice) allows the B screw to be adjusted so the RD is higher and makes for crisper shifting.


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## baker921 (Jul 20, 2007)

A sincere thank you to all contributors and I hope you had a chuckle at my predicament.

rx-79g - you are my "goto guy" for picture hanging. My wife wants the picture parallel to the door frame at the side, parallel to the picture rail at the top and in line with the pattern on the wall paper; oh and the house is 19th century and other than the kitchen units, which I installed, you wont find a level, straight edge or right angle in the place. Picture hanging usually ends up with grounds for divorce; what are you like on marriage guidance?

FBinNY - I agree about "half links" but in an effort to make sure i was understood managed to trip myself up.

Kerry - I think this "small small" method needs a degree of judgement best gained through experience.

Pacificalism - Your method really appeals to me but I suspect it works in most cases because the result always has to be rounded.

Danl 1 - the chain hook was the secret I was looking for. I found making the internal length 2 3/4" meant that it effectively covered six links. With my new best tool I was able to stop wrestling with the chain and concentrate on the business end of the operation. It was really easy to see what the other contributors were saying. Thankyou. 

So what did I find? 
The "big big" method suggested removing 5 1/2 links and I might have been tempted to remove six. Shimano method came out at four. "Small small" came out at just two but the derailleur was only just engaged. Zinn refers to this as the Campagnolo method and recommends a gap of 10/15mm between upper jockey wheel and chain. To achieve this four links was again the answer. I'm going to take out four links.
For any other newbs struggling with this in the future if you have a new derailleur you need to at least roughly set the top adjustment screw first to stop the chain walking up the cassette.
One last question. I've done this with the B screw fully backed out is this OK or is there now no fine adjustment in one direction.?
Once again many thanks to all contributors.


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## saddle tramp (Feb 22, 2006)

I've been using a calulator like this one all along. Never had a problem. I measure the thing out on the bench and make it the right length. Put on bike and ride.

http://www.epicidiot.com/sports/chain_length_calculator.htm#length_calculator

If you can do me a favor after all you combobulations do the calculator and see if it's close.


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## baker921 (Jul 20, 2007)

Sure. Giant TCX large Chainstay 430mm, compact 50/34 and 12/27 cassette. Result 110 links ie same as taking out four links. But their disclaimer doesn't fill me with confidence.
"Disclaimer: Always check to make sure the results are correct (preferably with an old chain) before breaking your good chain. We are not responsible for any errors in the calculation or mistakes. If you are not sure, add a few extra links, try it, and then shorten as needed."
My guess would be that some general assumptions must be made by the calculator since it must be doing a version of "big big + 2" since it ignores the number of rings you have and type of RD you are using.
For the sake of completeness I tried Pacificalim's calculation and it came out at 108 links.


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## tihsepa (Nov 27, 2008)

I have always got it right and never even knew all this complicated crap. Big, big +2 if its loose take another link out. It will be fine.

Jeebus Chisto.

Do you people build Steinways for a living?


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## Mike T. (Feb 3, 2004)

A from Il said:


> I have always got it right and never even knew all this complicated crap. Big, big +2 if its loose take another link out. It will be fine.
> Do you people build Steinways for a living?


You took the words outta *my* mouth. But for me big/big+2 has never been too big.


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## Kerry Irons (Feb 25, 2002)

*This is it!*



FBinNY said:


> Anyway, back to the OP original question there are three important chain lengths.
> 
> 1- *minimum length*, as determined by the big/big + 2 (1") method. There's no fudge room here. It's a true minimum length since otherwise the consequences of accidentally shifting into this combination are too serious.
> 
> ...


Excellent summary. I have yet to encounter a setup where the small-small setup didn't give the longest chain length, but I can imagine someone who made a big gearing change who would need to do both and then add a long cage derailleur.


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## Camilo (Jun 23, 2007)

pacificaslim said:


> I just calculate it.
> 
> Length of chain in inches equals the sum of:
> twice the chainstay length (round to nearest .125")
> ...


Hmm, I'm guessing you're an engineer?  

Now, joking aside, why would this be any more functionally accurate than the other methods


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