Optimal Chainlength - It's A New Day

Discuss light weight issues concerning road bikes & parts.
iamraymond
Posts: 57
Joined: Wed Jun 28, 2017 8:59 am

by iamraymond

Thank you very much for posting this!

I was in the process of setting up my R8050 and I used the big/big method + 1 link as I've always done. I was very worried that after I cut the chain and ran it through the RD in the big/big combo, that the chain was very tight. I adjusted the B screw a bit, went for a test ride, and the system shifts every combination decently.

So is my chain too short?

Here are some pictures in the big/big (50/32)
Attachments
IMG_4934.jpg
IMG_4935.jpg
IMG_4936.jpg

XCProMD
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by XCProMD

TobinHatesYou wrote:The simple equation is the mathematical equivalent of big-big sizing. It takes into account the amount of chain that goes around half the largest cog, half the the largest chainring, adds twice the distance of the chainstays and adds 1" (2 half links.) The only minor difference is the actual chain length between axle and spindle will be the hypotenuse of the right triangle where one side is the chainstay length and the other side is the difference in diameter between the cog and chainring. This can largely be handwaved away by rounding up the final value to the nearest integer.

There's no argument against this. It's primary education level math and whether you've incorrectly set up your rear derailleur is irrelevant. The output is the correct chain length.

In addition, I find it funny that Campy is using such a roundabout description for 12-speed. They're just saying a standard road bike with a 50t outer ring and a 32t largest cog requires 110 half links.

Let's do some math!

415mm = 16.3386in
2(16.3386)+(32/4)+(50/4)+1=54.1772
Round that value up to 55" = 110 half links!

Now you can say, but wait, Campy suggests the same 110 half links up to 53t chainrings. Well yes there is breathing room because we rounded up quite a bit in the 50t scenario and that number itself has some cushioning for the sake of safety. If we use a 53t chainring the math becomes:

16.3386*2+(32/4)+(53/4)+1=54.9272
Round that value up to 55" = 110 half links!

There's no magic here.

--

TL;DR If everyone just used the equation or its visual counterpart, life would be easier.
It looks to me like you are not taking the RD into account here. The latest derailleurs take some links themselves. That’s where Campag’s trick is

by Weenie


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Calnago
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by Calnago

iamraymond wrote:Thank you very much for posting this!

I was in the process of setting up my R8050 and I used the big/big method + 1 link as I've always done. I was very worried that after I cut the chain and ran it through the RD in the big/big combo, that the chain was very tight. I adjusted the B screw a bit, went for a test ride, and the system shifts every combination decently.

So is my chain too short?

Here are some pictures in the big/big (50/32)
It sounds as though your chain overlapped in the scenario where you could add one or three links. Personally, I’d never add just one, it just ends up being too tight for my liking. I showed examples of that earlier. While it works, barely, it’s putting a lot of stress on things and is invariably a lot noisier. Sometimes people seem confused over what one link, two links, or three links really is. I showed some pics earlier as to which to choose. It does look as though in your situation you had a choice of one link or three, and chose one.
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GothicCastle
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by GothicCastle

Calnago wrote:
Wed Jun 27, 2018 7:50 pm
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.
I just did the same thing. A 9100 bike and I noticed that the chain was on backwards. While flipping it around, I was sure that it was also too long; it seemed so slack before adjusting b-tension.

It wasn’t. The initial length was correct. After removing a link, the chain immediately got really noisy around the cassette.

I don’t think the Shimano docs are clear about this, but live and learn.

iamraymond
Posts: 57
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by iamraymond

Calnago wrote:
Sun Jul 22, 2018 2:35 am
It sounds as though your chain overlapped in the scenario where you could add one or three links. Personally, I’d never add just one, it just ends up being too tight for my liking. I showed examples of that earlier. While it works, barely, it’s putting a lot of stress on things and is invariably a lot noisier. Sometimes people seem confused over what one link, two links, or three links really is. I showed some pics earlier as to which to choose. It does look as though in your situation you had a choice of one link or three, and chose one.
Yes you’re absolutely right. I chose to add one link instead of three... it’s what I’ve always done in the past and unfortunately only read this thread after the fact. I’ll play it safe and add a couple links back into the chain.

bremerradkurier
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by bremerradkurier

Calnago wrote:
Tue Jul 03, 2018 6:46 pm
TonyM wrote:
Thu Jun 28, 2018 1:12 am
Back in the days (80s/90s, 8 speed) Shimano was stating that the correct length was big chainring - smallest cog and the pulleys should be straight.

Maybe because it was the recommended « optimal » gear at that time?? Everybody had big gears...
Ha... and I certainly remember those days. I was just as bad back then... if those pulleys didn't line up vertically with the axle, I couldn't sleep at night. :lol: But alas... in hindsight it was a good visual to ensure you were in the ballpark, whether it was very slightly off the veritcal axis or not was pretty irrelevant, as it was just a guide to follow. But oh, the nightmares I endured...
I'm really dating myself here-former US coach Eddie B. used to recommend overlong chains with the idea that a freewheel could function like a flywheel for some of those coveted marginal gains.

JScycle
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by JScycle

Hi,
Love this thread. I just read through it all and it is very informative.
I just checked my bike and in big big without running through the rear derailleur there is only one link added (using a quicklink).
I will add 2 more and was wondering if I can just use the Shimano joining pin to add these (only used quicklinks before) if so which side to I put it in from.

Also on another topic, I have an 11-32 cassette and mid cage rear derailleur which I switch over from my regular 11-28 cassette and short cage ultegra derailleur when I ride mountains. I only switch derailleurs because the ultegra short cage is limited to 11-28. I was wondering does big-big + 2 or 3 links (never 1!) work with a longer derailleur cage? Also is there any way to use the same chain in these two setups.

Thanks, love your work

JScycle
Posts: 216
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by JScycle

Hi again
It's running 52/36 chainrings with an 11-28 cassette in this photo.
On further inspection, without the quicklink the chain in big big is about 0.65-0.75 links extra with a quicklink making it 1.65-1.75 links.
Is this long enough? Photos attached below.
If you believe it is not enough I will add 2 links with a Shimano joining pin making it big big with about 3.65 extra links.

Kind regards,
Josh

Image

Image

LiquidCooled
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by LiquidCooled

JScycle wrote:Also on another topic, I have an 11-32 cassette and mid cage rear derailleur which I switch over from my regular 11-28 cassette and short cage ultegra derailleur when I ride mountains. I only switch derailleurs because the ultegra short cage is limited to 11-28.
Why do you change derailleurs? The mid-cage can handle both the 11-32 and the 11-28.
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JScycle
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by JScycle

LiquidCooled wrote:
Sat Jul 28, 2018 11:54 am
JScycle wrote:Also on another topic, I have an 11-32 cassette and mid cage rear derailleur which I switch over from my regular 11-28 cassette and short cage ultegra derailleur when I ride mountains. I only switch derailleurs because the ultegra short cage is limited to 11-28.
Why do you change derailleurs? The mid-cage can handle both the 11-32 and the 11-28.
Because it's rare I need those higher gears so I haven't bought another derailleur yet and im actually taking the midcage from my CX bike so puts that bike out of action.

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Calnago
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by Calnago

@JSccycle: most of the stuff in this thread relates to the newest derailleurs from Shimano, which have a lot of leeway with the b-screw to take up slack in a chain. It doesn’t look like you’re using the newest derailleurs.
In your pics of the 28 cog setup I’d probably just leave it as is.
If you’re going to be swapping derailleurs and cassettes with a large discrepancy in the largest cog I’d consider having either a couple chains (with quick links) or just use the med cage all the time as I think was suggested and see if that works ok for you. With the use of these monster cassettes you have to weigh 1) the convenience of always having the capacity to throw on the big cassette when you want, with 2) maybe a little less crisp shifting if you’re using it with a smaller cassette where the shorter cage might be a little better.
As to determining the chainlength when using the longer cage or the shorter cage, the method seemed to work well for both scenarios I was using... the shorter cage Dura-Ace cage or the GS cage of the Ultegra derailleur with the capacity for the 34 tooth cog.
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kdawg
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by kdawg

I wish I’d seen this thread a month or so ago. I just built up a new frame with 11spd Ultegra - first 11spd bike I’ve had. Used my usual method for chain length but I’m now thinking it’s a bit short. I’m using 50/34 and 11-32 - so I expected 50/32 (which obviously is never planned to be used) to be a bit extreme but it’s also slightly rumbly and I’m wondering if a couple extra links will fix that.

Here’s 50-11.
Image

And 34-11
Image

34-32
Image

And the problem one 50-32. Looks a bit tight to me?
Image

Should I add a few links. I think I still have the excess and the joining pin - this is joined with a quick link?
I'm left handed, if that matters.

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Calnago
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by Calnago

Yeah, that’s too short for my liking. Set it according to the methods I’ve shown in this thread, too long is not good either.
But big/big should not be considered a “Devils Choice” gear combo. While there’s better equivalent gears for sustained pedaling in that effective gear ratio, the big/big is an often used gear for a short stint, nothing wrong with that, so it should be useable without excessive noise and “rumblings”.
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kdawg
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by kdawg

Thanks for the super fast reply. I’ll see if I can find the links I removed. Unless there’s a problem with that and I should replace it?
I'm left handed, if that matters.

by Weenie


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themidge
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by themidge

^If anything, you could get away with the chain being a bit too long what with the long cage rear derailluer. There shouldn't be any problem with using the joining pin, Shimano recommends you use it, and their chains come with quick-links, so surely there can't be any harm in using both!

I have a chain length question too :D
I'm thinking of building a bike up with a 1x 10*, 40/11-32 and am a little confused about how the single chainring affects how you size the chain. So far (using 2x) I've used the formula method to satisfactory effect, but does it work with 1x? Should I size the chain using the biggest sprocket (shortest** possible chain) or the smallest (longest possible chain)? Using the big sprocket, I'm afraid the chain will be too slack in the smaller sprockets and I'll get excessive chain-slap, and using the small sprocket, I'm afraid I'll make the chain too short to clear the 32.

*with a short cage RD, should work given that there's less slack to take up with only one chainring.
**within reason of course.

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