Author Topic: Micro-vibrations on your bike  (Read 2749 times)

Andre Jute

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Micro-vibrations on your bike
« on: October 15, 2015, 10:18:02 PM »
From another thread, off on a tangent:

I have the 853 forks on my Sherpa, very pleased, but yes, not cheap.  They are a bit lighter than the standard forks, and also very comfortable - I have had much less problem with my arthritic wrist joints than on any previous bike.  Partly a better posture perhaps? but also less jarring through the forks.

You're touching on something really important here, Lewis.

I'm convinced a steel bike handles microvibrations better than an aliminium bike. If that is so, then it is only a small step to believing that some alloys of steel handle microvibrations better than other kinds.

The test of a well specified bike for me is how much better than a good ali bike it rides over the modern chip'n'seal surface. Micro vibrations are so common and so important and so little understood, that they're right at the top of my list of things to check for on any component exchange. They're at the root of comfort, fatique, and many localized problems like residual stress injury in your wrists even after you have achieved an optimally ergonomic position.

mickeg

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Re: Micro-vibrations on your bike
« Reply #1 on: October 15, 2015, 10:40:17 PM »
I have heard that some people feel slight vibrations from a dynohub at low speed, but I have not felt that on my Nomad.

Not only the metal or alloy, but also the thickness of the metal, and also the shape of the fork.  Decades ago when forks had a strong bend at the lower ends, I think they were a bit more springy too.  Example, my 1961 vintage Columbus tubing bike has the fork shape I am talking about in the photo.  (The bike has some modern components, do not let that confuse the issue, it is an early 1960s frame and fork.)


lewis noble

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Re: Micro-vibrations on your bike
« Reply #2 on: October 15, 2015, 11:40:23 PM »
Hello Andre and Mick . . . . Looks as though I've started something here!!

A lot of these 'opinions' are subjective guesses, I expect - I certainly don't have the technical knowledge, or experience on enough bikes, to be able to comment with authority.

But I have noticed that on my Sherpa, I am able to sustain reasonable speeds over poor urban surfaces better than pretty well any other cyclist, except perhaps people on top-end (and well maintained) mountain bikes.  Certainly better than pretty well any 700 wheel bike.  A common urban route of mine has a lot of speed bumps, right across the road, so they cannot be avoided - the the approach and descent surfaces are often rough and eroded.

The Sherpa just sails over, and I'm in one piece and perfectly OK afterwards! Part of this will be the fact that I stand up and let the bike 'ride', rather than hanging on like grim death, but a lot will I am sure be the spring in the forks - The Ripio I was riding up until the summer had Mt Tura forks - a pretty solid item, and not as comfortable over bumps, but still secure and manageable.

I haven't ridden an aluminum bike for any distance for some time, so cannot really compare.  But yes, the Rav 853 forks suit me very well.  I'm running on 1.6 Supremes, by the way, inflated to around 55 - 60 psi - not a very forgiving or absorbent tyre, though it rolls well and wuits me.

Lewis
 

JimK

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Re: Micro-vibrations on your bike
« Reply #3 on: October 16, 2015, 12:49:55 AM »
I have heard that some people feel slight vibrations from a dynohub at low speed,

I leave my Edelux light on the automatic setting. Sometimes I will be sailing down a hill, alternating between light and shadow. I can feel when the light kicks on in the shadow. I don't detect any drag but I do feel a little vibration. It seems to fade over maybe a minute. I think the higher draw when the capacitor is charging makes more vibration, then when the capacitor is fully charged the smaller draw means less vibration. I have a standlicht rear light too so that is two capacitors charging.

il padrone

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Re: Micro-vibrations on your bike
« Reply #4 on: October 16, 2015, 10:13:40 PM »
I have heard that some people feel slight vibrations from a dynohub at low speed, but I have not felt that on my Nomad.

Not only the metal or alloy, but also the thickness of the metal, and also the shape of the fork.  Decades ago when forks had a strong bend at the lower ends, I think they were a bit more springy too.  Example, my 1961 vintage Columbus tubing bike has the fork shape I am talking about in the photo.  (The bike has some modern components, do not let that confuse the issue, it is an early 1960s frame and fork.)
The existence of a bend set into the fork is of dubious effect upon resilience and vibration absorption. The major factors are always going to be metal type and especially thickness. The fork bend in older forks may have some impact, but is mainly there to set the geometry - to reduce the trail in a steep fork which otherwise would be far too stable. If you look carefully  at modern 'straight' forks you will see that they still have a bend in them - just that it is set into the fork right at the crown rather than along the blades. If you look at your 60s frame the fork is actually straight - in-line with the head tube - until the bend low down the blade. The crucial measurement is the position of the wheel axle relative to the steering axis and wheel contact point, and the overall head angle.

Be sure to check and compare your head angle - I reckon a shallower/steeper head angle will be of at least as much influence on road shock impact as a bend in the fork tip.
« Last Edit: October 16, 2015, 10:16:39 PM by il padrone »

mickeg

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Re: Micro-vibrations on your bike
« Reply #5 on: October 17, 2015, 12:12:17 PM »
I have heard that some people feel slight vibrations from a dynohub at low speed, but I have not felt that on my Nomad.

Not only the metal or alloy, but also the thickness of the metal, and also the shape of the fork.  Decades ago when forks had a strong bend at the lower ends, I think they were a bit more springy too.  Example, my 1961 vintage Columbus tubing bike has the fork shape I am talking about in the photo.  (The bike has some modern components, do not let that confuse the issue, it is an early 1960s frame and fork.)
The existence of a bend set into the fork is of dubious effect upon resilience and vibration absorption. ...

I disagree, I think that when there is a sharply angled curve at the bottom of the fork that the shape of the fork acts a bit like a mini-swing arm.  But, I do not want to get into a long argument on this, that is my opinion.

Danneaux

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Re: Micro-vibrations on your bike
« Reply #6 on: October 17, 2015, 04:39:24 PM »
Interesting topic, and one that provides great fodder for speculation, since the systems involved cannot easily be separated to assess their individual contributions/effects.

mickeg opined...
Quote
I disagree, I think that when there is a sharply angled curve at the bottom of the fork that the shape of the fork acts a bit like a mini-swing arm.  But, I do not want to get into a long argument on this, that is my opinion.
...and I agree but for somewhat different reasons. Speaking as someone who has sliced and sectioned a number of forks, I can say they do not remain constant in either wall thickness or section width/shape/diameter except for some straight-bladed forks which do remain constant in all those dimensions. Generally, as a result of the rolling and shaping process, straight and curved blades become smaller in diameter but at the cost of thicker walls when rolled down at their tips. Similarly, things differ up-top, with blade sections being either generally round or oval, and these all affect the actual flexibility of the blade along its length and bend/chord (or lack of it, in the case of straight blades).

For curved forks, placement of the bend really does change the flex characteristics of the fork, but more as a result of section width and shape and response to forces in the direction of travel.

Speaking as a hobbyist framebuilder, a factor commonly overlooked in comparing the flex of curved versus straight fork blades is the matter of blade length. Even if both kinds of forks have identical rakes (whether at crown or somewhere mid-blade) that result in the same offset (and trail, when combined with a given head angle and wheel/tire outside diameter), curved blades must be longer to get to the same place and will therefore flex along a greater length.

Fork crown design has an effect on fork flex and microvibrations as well. When a fork crown is inserted inside a fork rather than capping the blades, it has the effect of shortening the blade length -- or butting the upper section so massively as to change the fork's flex characteristics to a large degree. I've built forks that "felt" different but were identical in geometry and blades, but differed in crown style or construction (i.e. fabricated/stamped versus forged).

Steerer dimensions and head tube length and diameter probably have as much effect on microvibrations as other factors.

In my experience (and sadly -- except for generalities -- all we have is our own experiences and opinions, which are valid for us but devilishly hard to separate from myriad other factors in play. Because so many factors differ, ceteris parabis is out the window), the steerer, stem height/reach/construction, handlebars, and handlebar covering as well as the amount of rider weight placed on the handlebars -- and where -- are factors at least as large as fork rake and construction when it comes to feeling microvibrations in the hands and even body.  The larger threadless steerer on my Nomad is much larger in diameter than the threaded one in my favorite randonneur bike, and the quill stem on the rando bike visibly flexes -- and the handlebars are a different width, bend, and even wall thickness than those on the Nomad. I could surely feel a difference when I replaced the conventional headset locknut on the rando bike with a taller one (Sugino High Column Nut http://bmxmuseum.com/forsale/160507 ) that sleeved and supported more of the exposed length of quill. Compression-wrapping Grab-On foam grips with one or more layers of tape surely damped microvibrations by the time they reached my fingertips. Surely, some rubber brake hoods are more comfortable than others in this regard for me.

Tires (including tread design and pressure) play a huge role in the propagation or damping of microvibrations, as does the road surface. So do hub dynos. I have identical SON28s on my Nomad and most-favored rando bike, though wheel diameters and tires sizes and pressures differ. The one on the Nomad gives me no trouble, while the one on the rando bike produces such disturbing vibrations as to make riding the bike extremely unpleasant when using it at some speeds and unbothersome at others -- apparently from magnetic eddy currents producing vibrations that are transmitted through the hub to the axle and then through the fork to the handlebars where I have my hands. I blame some combination of fork design combined with my particular handlebar and stem. So far, my "solution" has been to ride at speeds above or below where the vibrations are most noticeable, but it is a nuisance on an otherwise viceless bike.

Micro-vibrations and their source(s) depend on many factors, but the degree to which they bother probably comes down to the most variable factor of all -- the individual rider.

Best,

Dan.
« Last Edit: October 17, 2015, 08:05:35 PM by Danneaux »

mickeg

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Re: Micro-vibrations on your bike
« Reply #7 on: October 17, 2015, 11:46:46 PM »
Dan, I suspect there may be some resonance issues on your rando bike dynohub vibrations as well.  Have you tried a heavier weight tire/tube combination?  If it is a resonance, changing the weight should change the natural resonance frequency.

Danneaux

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Re: Micro-vibrations on your bike
« Reply #8 on: October 18, 2015, 04:11:37 AM »
Hi mickeg!
Quote
Dan, I suspect there may be some resonance issues on your rando bike dynohub vibrations as well.
<nods> I agree, mickeg.
Quote
Have you tried a heavier weight tire/tube combination?
I sure did. I swapped to a heavier, 700x38C tire, but couldn't do much about changing the rim, because this is the only 700C wheel I have with this dynohub. It is a reasonably light touring wheel -- a SON28 with 36 3x butted 2.0/1.8/2,0 DT Swiss spokes and a NOS Mavic MA-2 rim. Default tire is a Bontrager Select K 32mm road slick. I tried the heavier tire and a heavier tube, but no change. I don't yet have the B&M e-Werk hooked up; it will be interesting to see what effect that has when charging.
Quote
If it is a resonance, changing the weight should change the natural resonance frequency.
I would have thought so, but no luck as yet. I may try tying weights to the spokes and see if a gross extrapolation of the thesis produces results.

The previous wheel is an identical Mavic MA-2 rim, but built with 36 3x DT Swiss 1.8g (straight, unbutted) spokes on a Phil Wood hub; this basic combo gave no trouble in over 32,000mi/51,500kms.

Handling with the dynowheel is as good as with the Phil-hubbed version.

Interestingly, I can duplicate the effect when the bike is hanging on its rack or when the bike is in the repair stand when the wheel is spun. It is nearly absent in my robust truing stand. I inserted the same wheel in several other bikes and while I can detect there is a vibration, it is not noticeable to anywhere near the same degree. After my father passed away, I inherited his identically framed bike and substituted this wheel for the 27in version in his with the same result, so it seems to be the combination of this wheel in these frames and thankfully is not a harbinger of individual fork or frame failure to come, else both bikes wouldn't produce the same result. Jack's has low mileage compared to mine.

I've substituted a Shimano internal-cam quick release for the standard SON28 bolt-on skewer, as I found it tended to loosen when torqued to specs, as it did on my Nomad. I am mindful of q/r tension, but variations did not seem to affect the vibration.

Best,

Dan.

mickeg

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Re: Micro-vibrations on your bike
« Reply #9 on: October 18, 2015, 12:46:22 PM »
...
I've substituted a Shimano internal-cam quick release for the standard SON28 bolt-on skewer, as I found it tended to loosen when torqued to specs, as it did on my Nomad. I am mindful of q/r tension, but variations did not seem to affect the vibration.

Best,

Dan.

On both my Thorns (Sherpa and Nomad) I have used Halo XL bolt on skewers.  They have not come lose on me, and I am careful to not over tighten them - the last thing I need on a trip is to strip out the threads on a skewer.  But I have no clue what the correct specification for torque is, do not use a torque wrench on them, so I really have no clue if I have over-tightened them.

If you are looking for a different bolt on skewer, I am quite happy with them.  The XL was needed for the thick dropouts on the Thorns, it is slightly longer than the non-XL version.  The Halo is a bit odd to use until you get used to them, there is only one spring, not the common two.  And a tab on the "nut" end that fits into the slot in the dropout to keep it from turning.  If you try them, be careful to make sure that the tab on the "nut" is properly placed before tightening them, otherwise you can bend the tab.

They use a normal allen wrench, not a special key to worry about losing.  I use them for touring because I am hoping that most thieves are opportunists that do not carry a 5mm allen wrench in their pocket.  I almost never lock both wheels to the frame when locking up the bike.

John Saxby

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Re: Micro-vibrations on your bike
« Reply #10 on: October 18, 2015, 04:26:17 PM »
+1 there, Mickeg.  I've just installed Halowheel skewers on my Raven, fore and aft.  (Robert Ewing on crazyguy had recommended these as well, a while back.)  My QR on the rear was working loose, although the SON28 hex-key skewer was fine.  Torque spec for both is 7 Nm. (SON says 6-8, Halowheel 7.)

I liked Halowheel's use of an anti-slip tab on the nut side of the skewer, which slots into the Raven's dropouts.

I've used these only for a few hundred kms, but so far, no hint of unwanted loosening.

martinf

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Re: Micro-vibrations on your bike
« Reply #11 on: October 18, 2015, 07:14:52 PM »
And another user of Halo allen-key skewers here.

When I ordered my first Thorn Raven Tourin 2012 I didn't want quick-release. Thorn proposed Pitlock, but I decided against that as I thought losing the special key (or just forgetting to take it on tour) would be an issue. So Thorn proposed Halo. They have been fit-and-forget so far.

I have other brands of allen-key skewers on other family bikes. No problems with them either, but the Halos seem to be better quality, and the tab is a nice feature.

Danneaux

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Re: Micro-vibrations on your bike
« Reply #12 on: October 18, 2015, 07:19:38 PM »
Thanks for recommending the Halo bolt-on skewers, fellows; much appreciated.

All the best,

Dan.

il padrone

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Re: Micro-vibrations on your bike
« Reply #13 on: October 20, 2015, 08:13:26 AM »
And another user of Halo allen-key skewers here.

When I ordered my first Thorn Raven Tourin 2012 I didn't want quick-release. Thorn proposed Pitlock, but I decided against that as I thought losing the special key (or just forgetting to take it on tour) would be an issue. So Thorn proposed Halo. They have been fit-and-forget so far.

I have other brands of allen-key skewers on other family bikes. No problems with them either, but the Halos seem to be better quality, and the tab is a nice feature.

We use Pitlocks. The key goes on my bike key-ring, and I carry a spare in my tool-kit. We have the set on my wife's bike keyed to the same code, so she carries another key as well. A key each and one spare, that will open both Pitlocks. There is a fourth key kept at home. We've not ever been caught out.
« Last Edit: October 20, 2015, 09:00:05 AM by il padrone »