Optimal Chainlength - It's A New Day

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Calnago
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by Calnago

Karvalo wrote:I have to admit, when I first saw this thread I kinda thought 'shouldn't everyone be able to figure this out anyway?' But it does seem like there are quite a few sub-optimal setups out there. And then there's this from Felt's 2019 promo...

Image
Image

What are we thinking, all good? :beerchug:
No, it’s not “all good”. Looks like a sloppy rush build job simply to get it ready for the photo shoot, but no one caught it in time before it was actually published.
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BdaGhisallo
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by BdaGhisallo

Calnago wrote:
Fri Aug 24, 2018 6:25 pm

No, it’s not “all good”. Looks like a sloppy rush build job simply to get it ready for the photo shoot, but no one caught it in time before it was actually published.
Someone must have purposely oriented the RD that way. Doesn't the RD-9150 come out of the box with the B Link fastened such that simply mounting the bolt to the dropout hanger puts everything in the right spot.

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Calnago
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by Calnago

There’s no way someone who knew what they were doing would intentionally mount it that way. And to your question about it only being able to be mounted correctly from the box, no, it’s easy to get the rear derailleur mounted in all sorts of weird ways (but this one is really whack). It’s far more common for the assembly to just get twisted rearward a bit while tightening it up, as the clockwise direction of tightening the bolt tends to want to turn it that way, away from the derailleur tab stop.
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Bigger Gear
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by Bigger Gear

Calnago wrote:
Thu Jun 28, 2018 6:35 pm
@Biggergear: I think you’ll be quite fine just sizing it for the 28 and adjusting the b-screw a bit when you throw on the 25. The difference isn’t that big and I don’t think it’ll be a problem. I’ve seen some big gaps where the owner thinks the shifting is “perfect”. It’s not but clearly it’s good enough. I suppose “perfect” is subject to interpretation. If you’re talking about a 25 to a 32 largest cog cassette, that may be different. But for those of us that like optimal shifting all the time, the thought of anything less is, well... I just can’t think about it.

I will be interested to see how the new Campy 12sp stuff plays out in this regard. Similar placement of the derailleur in space... we’ll see.
So just an update to this thread, as I had speculated about having an optimal setup for a tight range cassette and how much that might limit one going to a wider range cassette.

On my Moots running DA9100 mechanical with a 52-36 crankset and 12-25 cassette I was using 108 links. I've now swapped over to a 11-28 cassette and the chain length worked out fine. I first adjusted the B-screw tighter by ~ 3/4 of a turn to be able to clear the 28T cog in the small ring, then shifted down to the 11T and had to tighten ~ 1/2 of a turn further to acceptably take up the chain slack. Then I removed the chain and replaced with a new one at 110 links (with an old master link for test purposes only), and it was way too long. If I had the B-screw adjusted properly for the 28T then I had signifiicant chain slack starting at the 13T. So I cut the chain down to 108 and adjusted as previously. Shifting seems just as snappy as it was with the 12-25 cassette.

Now that I'm 50 I guess I have to get used to wider-range gearing, my days of stomping 39x23 up everything are behind me :lol:

K4m1k4z3
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by K4m1k4z3

What about the "in-between" scenarios.
For example my chain uses a quick-link and overlaps between 1 & 2 on the first quick-link photo. (R8000-SS RD btw)
A) I could either cut it at 2 adding 1.5 links. This is a bit tight in the extreme big-big combo to my liking, but "approved". Also I hardly ever use this gear.
B) Or I could cut it at 4 adding 3.5 links. This is much better in big-big, getting nice chainwrap all around on all gears, but provides little tension (if any) in the small ring + 11T/12T in the rear when the B-gap is adjusted properly for the 30T cog. But I also don't ever shift into that combination while riding.

Now would you keep the chain asap (as short as possible) and go with the A or stay on the side of caution and go with B? I'd leaning towards B personally.
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DaveS
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by DaveS

Keep in mind that chains can only be shortened in 2 link, or 1 inch increments and each inch reduces the available wrap by 4 teeth. Unless you are deliberately using a combination that exceeds the wrap capacity, it should be able to wrap the big/big and still provide tension in the the little/little. Since chainstay length affects the required chain length, all RDs should have excess capacity to handle any chainstay length. Virtually every bike is an in between situation. Few would have a chainstay length that calculates to a perfect 53, 54 or 55 inch length. Campy says to use the same 55 inch (110 link) chain for both the 11-29 and 11-32 12 speed cassettes.

The new 48/32 crank requires a 1 inch shorter chain. I use a 54 inch with 406mm stays. I have the 11-34 cassette. In theory, an 11-29 should work with a 53 inch chain.

TobinHatesYou
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by TobinHatesYou

Yep, still funny to me that so many words/photos were used just to say “set the b-gap correctly.”

DaveS
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by DaveS

I've never seen a b-screw adjustment require a different chain length.

Campy has revised instructions for chain length, but they all boil down to the length that provides some tension in the little/little combination, just as in the past.

See page 29. https://www.campagnolo.com/media/files/ ... 9_2019.pdf

TobinHatesYou
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by TobinHatesYou

DaveS wrote:
Wed Feb 19, 2020 8:16 pm
I've never seen a b-screw adjustment require a different chain length.

Campy has revised instructions for chain length, but they all boil down to the length that provides some tension in the little/little combination, just as in the past.

See page 29. https://www.campagnolo.com/media/files/ ... 9_2019.pdf

Sorry, wasn't responding to you, just that Calnago went on and on about chain length as if he made an incredible discovery. Turns out if you leave a setting completely out of spec, other settings can seem out of spec. Who knew?!

I'd forgotten about his tangent about Campy chain sizing, and the fact that he simply didn't understand that it all fits within range of the standard chain sizing formula.

AJS914
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by AJS914

I love how you find a 1.5 year old thread to cast shade on Calnago for no reason. He probably taught many people a few things just on the first page of this thread.

Maybe you should just block him and not read any thread started by him?

TobinHatesYou
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by TobinHatesYou

I didn't necro it and what specifically do you think it taught anyone at all? B-gap matters? Well of course it does. Now read the rest of the thread because my replies 1.5 years ago were more educational than the OP.

Karvalo
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by Karvalo

DaveS wrote:
Wed Feb 19, 2020 8:16 pm
I've never seen a b-screw adjustment require a different chain length.
But I have seen mechanics neglect to set B tension properly, cut a link based on small-small slack, then realise they've made the chain too short.

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ms6073
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by ms6073

AJS914 wrote:
Wed Feb 19, 2020 9:23 pm
Maybe you should just block him and not read any thread started by him?
Edit: No need. Cal has taken his final ride and as such, will never grace these forums again. :(
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SilverSwift
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by SilverSwift

Calnago wrote:
Thu Jun 28, 2018 12:32 am
@Wheelbuilder: Yup... sometimes the docs aren’t very clear. In particular the little diagram to tell where to cut the chain is more than a bit confusing. That’s why I created my own examples above as a little game... “where to cut the chain”.
Also, this is all related to what I started months ago in the thread about direct mount hangers. And just a day or two ago someone posted the statement to the effect of “... by all accounts the Direct Mount Hanger clears up the difficulty in rear wheel removal”. Aaach, i thought. No no no whether it’s a DM hanger or not, that is a separate issue entirely from the wheel removal issue. But it just made me more determined to finally create this thread which has been in the back of my mind for months now. Also, there was a thread about how noisy the new Shimano drive trains were with quite a few posters complaining about it. I asked if they could present some pics, but no one did. The reason I asked is because I thing the excessive noise they’re talking about could easily be caused by a chain that’s on the short side of optimal, which would be the case in Shimanos scenario that allows the addition of just one link. Like I tried to emphasize... always opt for the three in that case as one link extra is just not enough.

My next post on this will may be tomorrow morning and it will be just a continuation of that thread about DM hangers they I linked to earlier in this thread.
I have the noisy R8050 issue and would be very happy to post a picture of drive train. Which position should the mechs be in?
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DaveS
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by DaveS

With SRAM, the B screw is adjusted in the little ring and largest sprocket. Don't know about shimano.

Above, I read confusion about the definition of a link. A link is 1/2 inch long, but chains can only be shortened in 2 link increments. There is no 3 link change possible. Big/big plus 1 inch is always long enough, if measured properly. The formula for chain length also works perfectly. The two methods should always agree.

A chain is too long if it hangs loose or rubs on itself in the little/little.

https://www.parktool.com/blog/repair-he ... gth-sizing

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