Chordal action/purring vibration from drivetrain

Discuss light weight issues concerning road bikes & parts.
User avatar
Alexbn921
Posts: 294
Joined: Wed Apr 10, 2019 6:39 pm

by Alexbn921

Chordal action has a resonance frequency. Being in the big front ring will increase rear derailleur tension on the chain make it more noticeable. Changing chain length or adding weights to the frame around the drop out will alter the frequency. Even the stiffness of your rear QR can change it.
A dirty chain will make it worse.
The narrow or wide part of the chain interacts with the gears differently. Depending on your shifts you may get more or less side plate hanging on gears
A slightly out of adjustment rear derailleur will make it worse. Check that your hanger is straight.

Chordal action is always present, most of the time it just fades into the background noise. On the 10 tooth with a dirty chain, it is very noticeable, too the point of being annoying.

by Weenie


MaxPower
Posts: 49
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

Mounted absolute black oval rings. 50/34 again, as i just can't push bigger gears (doggy knee).
Sadly I'm sick at the moment, so no ride on the bike, but it seems that the vibration can still be created on the stand in the 12t cog.

Oh well, wanted to go back to ovals anyway.

Will try a different chain length when i need a new chain again (some time). Have different QR at home, will give it a try (but not super optimistic about it).
RD hanger is straight (aligned with prober tool)

MaxPower
Posts: 49
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

hm... it seems that with a lighter (ti) QR it will vibrate a little less. its still very noticable in the 12t, but definitly less.
Might give the lighter QR a go. i normally use heavy steel QR (because they just feel so much more robust)

JerryLook
Posts: 293
Joined: Thu Dec 07, 2017 2:18 am

by JerryLook

I’ve had the same issue with one of my bikes for a while. I’ve changed out everything you have with the only slight improvement being when I aligned the RD hanger.
I run a 53/39 chainring and 11/23 cassette setup. The vibration is only in the two smallest cassette cogs.
2010 Orbea Opal 54cm
5.97kg

MaxPower
Posts: 49
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

just ordered a longer chain to try - found out shortly after i ordered it that i probably can´t really run longer chains, as small/small actually takes up almost the complete travel og the RD cage (although i will never run it like that, as use of small chainring+highest 3 cogs is like the bad´est idea ever anyway with oval rings)
will give it a try though and report back :-D

MaxPower
Posts: 49
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

JerryLook wrote:
Sun Sep 29, 2019 4:23 pm
I’ve had the same issue with one of my bikes for a while. I’ve changed out everything you have with the only slight improvement being when I aligned the RD hanger.
I run a 53/39 chainring and 11/23 cassette setup. The vibration is only in the two smallest cassette cogs.
Thanks for the reply - not optimistic, but at some point i will probably have to accept it as is. Used some money, used a lot of time thinking and tinkering - so in the end cycling fun :-D

P.S i am actually pretty suprised at absolute black chainring shifting. it´s a lot better then 10 speed SRAM red with Rotors Q-rings (that would through the chain all over the place regularly)...

Now - only need to get through the illness...

MaxPower
Posts: 49
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

Hm... Conclusion (for mig case) :
Chain length does nothing to alter it. Oval ring change it a little bit (more together with a kmc chain).
Kmc chain alone helps to dampen it a bit compared to shimano chain.

Derailleur cage tension makes no difference.

So, i just have to live with it then.
But found out that the shimano chain is a tiny bit narrower than the kmc - at i prefer it with the r8000 front derailleur (such a pain to adjust just right, and the narrower chain gives less chain rub at the extrem gearing.

MaxPower
Posts: 49
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

Probably last update.
Found a dura ace chain with the sil-tec treatment on thw rollers to, plus hollow pins.

This helped some with the vibrations. It's still there, but less and most low cadence and lower teeth cogs.

fizzaz
Posts: 30
Joined: Wed Nov 07, 2018 5:02 pm
Location: Nashville, TN

by fizzaz

I do not have a solution, but i have struggled to explain the exact issue you are having. This has happened to me on multiple bikes and groupsets and speeds and never been able to deduce the cause. From di2 to 105, it has happened. Even with multiple chain suppliers.

TheKaiser
Posts: 644
Joined: Thu Sep 05, 2013 3:29 pm

by TheKaiser

MaxPower wrote:
Mon Oct 28, 2019 2:50 pm
Probably last update.
Found a dura ace chain with the sil-tec treatment on thw rollers to, plus hollow pins.

This helped some with the vibrations. It's still there, but less and most low cadence and lower teeth cogs.
It sounds like you have been very thorough in your troubleshooting. I, for one, would be interested in hearing further updates if you get any more insight in the future. For example, if you got a new frame (not worthwhile for this issue, but just in due course), and swapped your parts, does the problem remain? Similarly, if you got a whole new bike of a different make, or rented/borrowed a friends, with R8000, do you notice the same issue? Both questions are rhetorical at this point, but it would be interesting to know if there is some sort of unusual system resonance going on with your setup, or if you are perhaps just more sensitive to the normal everyday mechanical "noise" that most other users simply don't notice.

I'm also curious about what you find with the D-A chain with the sil-tec. Most new chains come out of the package with a very thick grease applied, so it would be interesting to see if that has any damping effect vs. the standard drip on which you typically use. If the D-A chain does improve your situation, it would also be interesting to know if degreasing it and then re-lubing with Squirt or whatnot changes it for the worse.

For my part, I have noticed what seems like a chordal vibration through drivetrains before, although, much like Alcatraz said, it is usually only on overly worn drivetrains with a sloppy chain/cassette interface, and it was noticeable in many of the gears. On the flip side, I have also had a situation where I bought some off brand parts to rebuild an old frame into a winter beater. On initial install I found that there was an odd resonance occurring on just a single cog, somewhere in the middle of the cassette, but every other gear worked great. From memory, maybe the 15t or 17t. After going through the whole array of possibilities (hanger/cable/etc...) and watching the chain/sprocket interface up close as I pedaled very slowly on the stand, I came to the conclusion that there was something off with the manufacture of that one cog. Don't know if it was the pitch, or something else, as it is very difficult to measure these things, but I went ahead and rode it and either it wore in or else the other noises and distractions of the open road made it unnoticeable in the real world.

It is interesting that, in your case, you do not notice the issue in the 11t, as chordal action is said to be worse as cogs get smaller, which is the reason that Shimano and Sram have only gone down to a 10t on their 1x MTB drivetrains. E-13 makes a cassette with a 9t, and I have heard mixed reports on how rough it feels. The resonance and natural frequency of a system has many factors though, so I suppose you may have just struck on a (unfortunate) perfect mix in the 13t and 12t, whereas the 11t puts it out of phase.

P.S. I don't have time to look it up right now, but I recall a thread on here within the past year that had to do with people feeling that R9100 ran "rougher" in terms of chain/sprocket pedaling feel than their previous groups. I don't know if you've seen it, but it seems somewhat related and thought you might want to give it a look.

MaxPower
Posts: 49
Joined: Fri Sep 20, 2019 9:30 pm

by MaxPower

TheKaiser wrote:
Tue Oct 29, 2019 1:51 am
MaxPower wrote:
Mon Oct 28, 2019 2:50 pm
Probably last update.
Found a dura ace chain with the sil-tec treatment on thw rollers to, plus hollow pins.

This helped some with the vibrations. It's still there, but less and most low cadence and lower teeth cogs.
It sounds like you have been very thorough in your troubleshooting. I, for one, would be interested in hearing further updates if you get any more insight in the future. For example, if you got a new frame (not worthwhile for this issue, but just in due course), and swapped your parts, does the problem remain? Similarly, if you got a whole new bike of a different make, or rented/borrowed a friends, with R8000, do you notice the same issue? Both questions are rhetorical at this point, but it would be interesting to know if there is some sort of unusual system resonance going on with your setup, or if you are perhaps just more sensitive to the normal everyday mechanical "noise" that most other users simply don't notice.

I'm also curious about what you find with the D-A chain with the sil-tec. Most new chains come out of the package with a very thick grease applied, so it would be interesting to see if that has any damping effect vs. the standard drip on which you typically use. If the D-A chain does improve your situation, it would also be interesting to know if degreasing it and then re-lubing with Squirt or whatnot changes it for the worse.

For my part, I have noticed what seems like a chordal vibration through drivetrains before, although, much like Alcatraz said, it is usually only on overly worn drivetrains with a sloppy chain/cassette interface, and it was noticeable in many of the gears. On the flip side, I have also had a situation where I bought some off brand parts to rebuild an old frame into a winter beater. On initial install I found that there was an odd resonance occurring on just a single cog, somewhere in the middle of the cassette, but every other gear worked great. From memory, maybe the 15t or 17t. After going through the whole array of possibilities (hanger/cable/etc...) and watching the chain/sprocket interface up close as I pedaled very slowly on the stand, I came to the conclusion that there was something off with the manufacture of that one cog. Don't know if it was the pitch, or something else, as it is very difficult to measure these things, but I went ahead and rode it and either it wore in or else the other noises and distractions of the open road made it unnoticeable in the real world.

It is interesting that, in your case, you do not notice the issue in the 11t, as chordal action is said to be worse as cogs get smaller, which is the reason that Shimano and Sram have only gone down to a 10t on their 1x MTB drivetrains. E-13 makes a cassette with a 9t, and I have heard mixed reports on how rough it feels. The resonance and natural frequency of a system has many factors though, so I suppose you may have just struck on a (unfortunate) perfect mix in the 13t and 12t, whereas the 11t puts it out of phase.

P.S. I don't have time to look it up right now, but I recall a thread on here within the past year that had to do with people feeling that R9100 ran "rougher" in terms of chain/sprocket pedaling feel than their previous groups. I don't know if you've seen it, but it seems somewhat related and thought you might want to give it a look.
Thanks for the reply. It is ok now I think. Its just sn issur indoors because of hardwood flooring. Outside its a non-issue. In the beginning I thought it was jusy tarmac roughness when going fast :-D

About lube: i run it the first 20-25 km with factory grease and than degreased it and applied squirt. Its actually less vibrant with squirt. And less noisy as well.

Post Reply
  • Similar Topics
    Replies
    Views
    Last post