Optimal Chainlength - It's A New Day

Discuss light weight issues concerning road bikes & parts.
TobinHatesYou
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by TobinHatesYou

Shimano isn’t giving you the option of adding 1 or 3 links...they needed to change the semantics a bit. They started packaging quicklinks and that provides an allowance of half a link in either direction. Basically what they’re saying is if the two inner links overlap quite a bit, just add the quicklink. If they don't overlap, add the quicklink and an extra inch. This is why the Park Tool video you referenced explicitly says to include the quicklink during measurement to avoid confusion.

We all know that derailleurs have X capacity. The medium cage Shadow models can take up 39t officially, so obviously you could use the small-small method and have the longest chain possible just in case you want that monstrous 11-34t down the road. That’s fine if you’re unwilling to have a second chain, and because Campy in particular has not embraced quicklinks. So size your chain using the equation and the largest cog you plan on ever using if won't be swapping chains. I'll give you that. This however is WW after all and extra links are gonna cost you grams.

Also I say to round up as a precaution. You may round down if the decimal is very close, but rounding up is safer given the chains are angled on two planes, increasinf their length relative to the shortest distance possible (chainstay length.)

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TonyM
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by TonyM

I do like GCN but the videos are actually made for cyclist beginners.... :mrgreen:

WW is a much better place for deeper understanding etc.... :smartass:
Thanks to users like Calnago :thumbup:

by Weenie


TobinHatesYou
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by TobinHatesYou

To put it into real world perspective. Let's say I were to install 12spd Campy on my bike. In all likelihood I will never switch out of the 50/34t out front, and I will also primarily use the 11-32t in the rear. With 410mm / 16.1417in chainstays, I would end up with a perfect chain length of 53.7834in...rounded up to 54" = 108 half links. Why should I follow Campagnolo's directions and include those 2 extra half links? That extra inch of chain serves no purpose when 54" of chain is comfortably slack. It's certainly more slack than the example of a 415mm chainstay length and 53/39x11-32t with 110 half links.

To an extent I appreciate Campagnolo trying to simplify their guidelines for the layman, but that's not us.

kafreeman
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by kafreeman

I put a RD8000GS on my cross bike, moved the 6800SS that was on it to the crit bike.

1st thing I noticed, much higher spring tension. Loads more chain wrap.

2nd wheel removal and install sucks now. Lining up the disc into the caliper and pulling the derailleur back to even get the wheel in is a pain. Only removed twice so maybe a technique thing. It is a QR rear.

3rd chain length... already had it long from a 50 to 46 chainring swap. 6800 barely had enough tension on it. Put the quick link in so gained another half link. Large small looks ok, need to review it again since I havent ridden it much due to bending a rim on a pothole and work. Shimano tech doc was a bit hazy on sizing so I errored on the long side of things. Big big + a few. If I remember right pully cage is a bit past horizontal.

Finished swapping the rim the other day so need to get it out on the road a bit.

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Calnago
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by Calnago

What is clear to me is that Tobin doesn’t have a clue, again. But I did manage to enjoy a lovely dinner out despite it all.
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TonyM
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by TonyM

kafreeman wrote:
Thu Jun 28, 2018 4:32 am
I put a RD8000GS on my cross bike, moved the 6800SS that was on it to the crit bike.

1st thing I noticed, much higher spring tension. Loads more chain wrap.

2nd wheel removal and install sucks now. Lining up the disc into the caliper and pulling the derailleur back to even get the wheel in is a pain. Only removed twice so maybe a technique thing. It is a QR rear.

3rd chain length... already had it long from a 50 to 46 chainring swap. 6800 barely had enough tension on it. Put the quick link in so gained another half link. Large small looks ok, need to review it again since I havent ridden it much due to bending a rim on a pothole and work. Shimano tech doc was a bit hazy on sizing so I errored on the long side of things. Big big + a few. If I remember right pully cage is a bit past horizontal.

Finished swapping the rim the other day so need to get it out on the road a bit.

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Do you mean the "regular" Ultegra derailleur or the new "RX" Ultegra derailleur with the clucth?

kafreeman
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by kafreeman


TonyM wrote: Do you mean the "regular" Ultegra derailleur or the new "RX" Ultegra derailleur with the clucth?
Regular derailleur. Rx8000 wasn't announced yet. Picked up 9000 shifters and brakes off ebay and moved the derailleur.



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Svetty
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by Svetty

Calnago wrote:
Thu Jun 28, 2018 4:34 am
What is clear to me is that Tobin doesn’t have a clue, again. But I did manage to enjoy a lovely dinner out despite it all.
The problem with an obsessive attachment to the equation is that it assumes a constant percentage of wrap across all gruppos and bikes - which isn't necessarily optimal.....

TobinHatesYou
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by TobinHatesYou

Svetty wrote:
Thu Jun 28, 2018 10:39 am

The problem with an obsessive attachment to the equation is that it assumes a constant percentage of wrap across all gruppos and bikes - which isn't necessarily optimal.....

The way I see it, Campagnolo is defining 55" as "adequate" for 405mm chainstays, 11-29t cassettes and 50/34 chainrings as well as 415mm chainstays, 11-32t cassettes and 53/39 chainrings. I don't consider it the optimal chain length for the former. The benefit here is flexibility for component swaps.

kafreeman
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by kafreeman

Derailleur at max capacity.Image

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Calnago
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by Calnago

@kafreeam... so that pic is big/big, right? Plenty of length there. Close to cassette. Do you have a pic of small/small (it’s mechanical right?).
Last edited by Calnago on Thu Jun 28, 2018 2:28 pm, edited 1 time in total.
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TobinHatesYou
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by TobinHatesYou

Kafreeman, what do you mean you gained a half-link by putting the quicklink in? In order to use a quicklink where there previously wasn’t one, you must remove one outer link. You can’t gain a half link in length on a previously joined chain just by adding a quicklink.

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Calnago
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by Calnago

Also, @Kafreeman... not sure what your issue really is but if it’s concerning the difficulty in wheel removal, that’s a separate issue from chainlength and I’ll get to that hopefully a bit later this morning. Gettting the chainlength right is just the first step in getting the new Shimano drivetrains set up optimally. That’s why I felt this thread was a necessary preamble before delving into that topic again.
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Calnago
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by Calnago

Ok, before things get too far derailled (hey, would that be a pun in the context of this thread), I'm going to try to finish up what I started this thread for then move on to the more interesting part of how it all relates to setup, the DM hanger scenario, what SKY is doing, and what you can do to make rear wheel removal easier if that's an issue for you with the new derailleurs.
But first... I played around with this stuff extensively over last winter both to thoroughly educate myself first hand but also wanted to show what a proper set up should look look like when everything is "right".... correct chainlength for the drivetrain, compatible parts, and perfect adjustment of the new, highly sensitive, B-screw.

So, first here's a series of pics of a drive train that's perfectly set up in the various combinations of interest....

Example 1: Standard rings 39/53, 11/28 casssette
The drive train in this example consists of standard 39/53 rings up front and 11 spd 11/28 cassette at the rear, all the latest Dura-Ace. I played around with the correct length chain and experimented with what would happen if the chain was a tad too long (didn't bother with too short as that would rip off the derailleur). Here's some pics of how things should look with the correct length chain, and the B-screw adjusted properly...

Combo 1: Small ring/small cog....
Image


Combo 1 Closeup Small ring/Small cog: Note the interface with the cassette and chain and upper pulley... in all cases that I show note how far forward of the rear axle the upper pulley is, and also how close I can get it to the cogs themselves, regardless of the drivetrain combinations...
Image


Combo 2: Small ring/Large cog...
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Combo 2: Closeup Small ring/Large cog...
Image


Combo 3: Large ring/Small cog...
Image

Combo 3: Closeup Large ring/Small cog...
Image


Combo 4: Large ring/Large cog...
Image

Combo 4: Closeup Large ring/Large cog...
Image


There you have it, a perfectly set up and adjusted Shimano drivetrain. No Direct Mount hanger... just the regular hanger and the provided B-Link from Shimano. The setup is identical in both cases, as the derailleur is positioned in the same exact place no matter if you have a DM hanger or a regular hanger plus the B-link. In conclusion, once again, the minor annoyance in rear wheel removal over previous versions is the tradeoff for having the derailleur top pulley so far forward of the rear axle, and that has nothing to do with whether a DM hanger or a regular hanger is used. But look at that wrap and engagement of the chain, all before the 6 o'clock position of the cogs. This makes for crisp, accurate and fast shifts. It's a delight on a fast road machine just clicking through the gears. Set up correctly, the new derailleurs from Shimano are great. They shift super smooth. There may be the odd frame here and there that really doesn't play well with the new stuff as far as wheel removal goes, so that should be paid close attention to for sure. On that note and before I forget, after playing with this one for a bit, and twisting and turning things without the chain on it and with the chain on it, I would strongly advise against any grinding away of the "stop" built into the B-link. I can see now why it's there... pulling the derailleur back farther than that stop puts a whole lot of stress on the pulley cage, and I was hearing unpleasant creaks and crackling noises when I experimented. That stop is there for a good reason.


Example 2: For completeness'... here's a second example consisting of an Ultegra 8000 GS derailleur and the monster 11/34 cassette.

Combo 1: Large Chainring 52 / Largest Cog 34
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Combo 1 Closeup: Largest Chainring 52 / Largest Cog 34
Image


Combo 2: Small Chainring / Largest Cog 34
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Combo 2 Closeup: Small Chainring / Largest Cog 34
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Combo 3: Small Chainring 36/ Smallest Cog 11
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Combo 3 Closeup: Small Chainring 36/ Smallest Cog 11
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Combo 4: Large Chainring 52 / Smallest Cog 11
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Combo 4 Closeup: Large Chainring 52 / Smallest Cog 11
Image

So there you go, if you can't get your setup to look like these pics, then something is probably not quite right somewhere along the way, and that could very well be your chainlength. The whole setup today is so much more sensitive to having all the variables set just right, as the interaction between them all can play tricks with your head. I wanted to test what happened when the chain was a bit too long, just two links, the minimum amount you could actually lenghten a chain. Each case has it's specifics but there were cases where if the chain was just that much too long, I could not get the whole system as perfectly adjusted as in the above photos, as I would have to tighten up the B-screw in order to take up the slack, but in so doing that invariably pulls the upper pulley further away from the cogs as well. It all works and is pretty easy when you've sat down to figure it all out and done it enough times, but when you just start playing with it coming from the older stuff, it's not quite as intuitive as you might think. I should have posted this months ago for sure, but it's still apparent that there's a lot of folks that might benefit even from the knowledge that "things ain't like they used to be" and thus be a little more aware of some of the pitfalls you might face.

Other tidbits you might want to know about...
Regarding the lockout of the smallest two cogs with Di2. I've seen a video where it was surmised that the reason for the lockout was because you wouldn't be able to take up the slack in the chain otherwise if the chain were on the small ring up front and either of the two smallest cogs at the back. That is not true. In the examples I've shown above, there is no slack in the chain regardless of the combinations of gears being used. It's all about getting the right balance amongst everything.

And I may as well insert the relevant information on setting the chainlength per the Shimano Dealers Manual here. But note, the one scenario I've been advising against using anytime is example [2] in the diagram below, Option (Y) - the addition of 1 link. If you use one link here, you will end up with the short chain that I presented earlier in the thread. So, use three links always in that case. Also take into account whether you're using a quick link or not. I tried to show both examples earlier in my actual photos of the chains laid out with the quiz on where to cut them. Those photos are consistent with the diagram below...
Image

Well, that's it for now. I will go into a few "tricks" to get around the issue of difficult wheel removal in the next installment. The example bike at the beginning of this thread is the perfect model for this, because not only does it show the case where it's quite possible to come up with a chain that's technically correct, but practically way too short... it also has the issue of difficult rear wheel removal. In fact, you can't remove that rear wheel without deflating the tire first. Ha... just a teaser... so stay tuned.

Cal
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by Weenie


Bigger Gear
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by Bigger Gear

I think one of the unfortunate downsides to the 91xx/80xx series is that for a rider who has multiple wheels and likes to use different cassette combos then chain sizing the new Shimano way is a bit of problem. For example, I have 12-25 cassettes that I use for most of my flat/rolling riding around home. But I also have 11-28 cassettes that I prefer if I am ridign in mountainous terrain. Ideally now, I think I would need a longer chain when going from the 12-25 to the 11-28, but I haven't played around too much to see if that is the case.

Thanks for the detailed work here Cal!

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