KVA butted tubing-ride quality

[Mark Kelly]

I should have added:

In the presence of excitation (forcing) the resonance will build amplitude until the rate of energy loss from the damping equals the energy input from the excitation. Damping thus determines the amplitude of the resonance when forced.

I am of the opinion that this is an important effect in bicycles. It becomes really important when combined with the frequencies determined by the structure and material.

[Burnette]

Want to have a bike built, been reading and riding to learn what I can.
Have to get up early to take baby girl to school and try and get a ride in before work in the afternoon.
Peeked into this thread, intersting, then Bam!, I hit this:

e-RICHIE



Re: KVA butted tubing-ride quality
I kneel at the feet of anyone who can tell what brand of tubing, what gauge of tubing, or even what
diameter of tubing their steel frame is made from atmo. The last example has to be done blind - ha.

Again - http://www.velocipedesalon.com/forum...ize-21480.html

That old thread. Damn it, what a freakin rabbit hole I jumped in, wholy hell, man.
Really loved it, much meat for me, even got my fave Dave Anderson in there!
Saved to favorites, will read again, will go to bed thinking it's OK that I don't need magnums. Ha!
You'll have to read the thread to get that.
Checking out, OCD is a &itch. Thanks alot e-RICHE

[steve garro]

Steve

Damping affects the envelope of the resonance but at the levels we are talking about it doesn't affect the frequencies.

Frequencies are determined by the shape and bulk properties, especially the propagation velocity which is the square root of the quotient of stiffness and density. There is also an affect from reflection / dispersion at material boundaries which is strongly influenced by the difference in acoustic impedance between adjacent materials. Acoustic impedance is again a bulk property only this time it's the product of the density and the propagation velocity, which in turn means it is the square root of the product of density and stiffness.

I initially thought resonances were important but I have resiled from this.

As a basic primer: anything which is springy will have a number of vibration modes which occur at frequencies determined by the interchange of energy between kinetic energy and elastic deformation. Stiffer systems return energy faster, so frequencies increase. More massive systems store more kinetic energy so for a given rate of energy return (stifness) the frequency decreases. Energy is always lost from the system, so the resonance alsways decays unless there is an excitation source present. The rate of loss is partially determined by the internal damping of the system: greater damping = faster loss = shorter resonance.

What if you end up with one that goes full on "Tacoma Narrows Bridge" on you?
:)
- Garro.

[Alistair]

Mark,

do you think is there a connection between the mechanisms you're describing here and the phenomenon that some (the guys over at Bicycle Quarterly coined the term I believe) have come to describe as "planing"?

Might they be different ways to try and quantify the same phenomenon?

Some very interesting insights by you in this thread. Thanks for posting them.

Alistair.

Steve

Damping affects the envelope of the resonance but at the levels we are talking about it doesn't affect the frequencies.

Frequencies are determined by the shape and bulk properties, especially the propagation velocity which is the square root of the quotient of stiffness and density. There is also an affect from reflection / dispersion at material boundaries which is strongly influenced by the difference in acoustic impedance between adjacent materials. Acoustic impedance is again a bulk property only this time it's the product of the density and the propagation velocity, which in turn means it is the square root of the product of density and stiffness.

I initially thought resonances were important but I have resiled from this.

As a basic primer: anything which is springy will have a number of vibration modes which occur at frequencies determined by the interchange of energy between kinetic energy and elastic deformation. Stiffer systems return energy faster, so frequencies increase. More massive systems store more kinetic energy so for a given rate of energy return (stifness) the frequency decreases. Energy is always lost from the system, so the resonance alsways decays unless there is an excitation source present. The rate of loss is partially determined by the internal damping of the system: greater damping = faster loss = shorter resonance.

[shiggy]

What if you end up with one that goes full on "Tacoma Narrows Bridge" on you?
:)
- Garro.

You crash

[steve garro]

You crash

HA!
I'm always amazed at what the metal is doing, I've watched this a bunch of times!
I always tell metalworkers to read "How Buildings Fall Down" - so many lessons to be learned from other's failures.
Applies to bikes 100% + a super great read, worth the hand drawn illustrations alone.

MK: are you channeling Tesla?
“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”

― Nikola Tesla


- Garro.

[Will Neide]

“If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.”

― Nikola Tesla

Would have made a great pick up line in college.

[jclay]

Alistair & Mark,

It seems to me that the properties Mark broached are at least in part responsible for the existence of strain energy behavior. In that sense they would be the under-pinnings of the macro frequency response of structures, be they the strings in a tennis racket, golf club shaft, bridge or even (gasp) a bicycle frame. As to planing, keeping the same area under the strain energy curve (or pedal force curve) by broadening the curve shape and reducing peak magnitude would, I believe, enhance propulsion efficiency (like a smoother pedal stroke does) and reduce muscle fatigue (by reducing peak fiber tension); ignoring other considerations that would seem beneficial.

[progetto]

Are we talking about bicycles here or something else?

[e-RICHIE]

Are we talking about bicycles here or something else?

Something else atmo.

[Mark Kelly]

Mark,

do you think is there a connection between the mechanisms you're describing here and the phenomenon that some (the guys over at Bicycle Quarterly coined the term I believe) have come to describe as "planing"?

Might they be different ways to try and quantify the same phenomenon?

I think they are only peripherally related, the frequencies of resonance which are important for ride quality are well above the forcing frequencies represented by pedal mechanics. In my opinion there is an important link via the frequency dependence of damping; most metals have constant loss angle with frequency but composites exhibit far more complex behaviour.

I originally wrote a long post on the mechanics of "planing" but decided it wasn't really germane to the discussion.

[jclay]

Imagine you measured the chain tension at each degree of the crank, 0 through 359, at a constant 250 watts but for two pedaling styles; one very punchy, one far more uniform throughout the 360 degrees. Plot the two sets of data (tension vs angular pedal position) and draw a smooth curve through them. The area under the two curves, representing a proxy for energy, will be identical but the "punchy" curve will be skinnier and with taller peak stresses (indicating higher max chain tension) than the other which will be fatter and not as tall (indicating a lower max tension). Ask yourself which is more efficient to propulsion, the punchy one causing exaggerated acceleration/deceleration of the bicycle (due to the exaggerated chain tension spikes), or the other with its more uniform chain tension? I suggest it's the latter. Also ask which one would visit the highest max muscle tension on the rider. Again, the latter seems a safe bet. Now, add to this the impact that the effect of frame strain energy storage and release would have to further smooth the curves; I suggest it would be similar to having the chain act like a spring, of suitable "springniess", neither too springy nor too stiff. The result would be a more uniform chain tension (and more uniform power delivery) with a reduced max muscle fiber tension. Both would improve efficiency and performance. That is what I believe is behind "planing". One thing I know with certainty; different tube diameters and wall thicknesses do affect frame behavior and have to affect, one way or another, propulsion efficiency regardless of whether or not a particular rider can discern it; it is what it is. One frame or 10,000 frames under your belt, physics doesn't care what any of us think or feel.


Sent from Yahoo! Mail for iPad

[Alistair]

Are we talking about bicycles here or something else?

Bicycles, most definitely.

[Dallas Tex]

zzz Loch-ness-monster_1466828c.jpgzzz alien magesCA2D3FVI.jpgzzz Big foot.jpg

I couldn't find a picture of 'planing'.......

[Steve-O]

Hey gang... Sorry to get off the tech discussion... Several years ago I had a Colombus XCR frame built for me by Paul Taylor. After roughly 1500 miles the frame got destroyed in an accident. Paul built me up a frame with the same dimensions out of KVA stainless. Components were transferred over thus I had a pretty close comparison. The nuances were very slight between the two frames. I put roughly 3000 miles on the KVA frame. The KVA came out slightly lighter (maybe 3-4 ounces - mostly due to a machined headtube). It seemed a little more springy then the XCR frame. If you blindfolded me and asked me to ride them I could not tell the difference...

Unfortunately I can't help with tube thicknesses, butt lengths etc. As a customer, I was kind of stoked on the made in the USA thing with KVA. Thats about it!

[blasdelf]

Hey gang... Sorry to get off the tech discussion... Several years ago I had a Colombus XCR frame built for me by Paul Taylor. After roughly 1500 miles the frame got destroyed in an accident. Paul built me up a frame with the same dimensions out of KVA stainless. Components were transferred over thus I had a pretty close comparison. The nuances were very slight between the two frames. I put roughly 3000 miles on the KVA frame. The KVA came out slightly lighter (maybe 3-4 ounces - mostly due to a machined headtube). It seemed a little more springy then the XCR frame. If you blindfolded me and asked me to ride them I could not tell the difference...

Unfortunately I can't help with tube thicknesses, butt lengths etc.

The KVA's butts are probably shorter on the short end and longer on the cut end

Columbus mostly hews to 0.75/0.45/0.75 where KVA is 0.7/0.4/0.7, but if you order tubes in light bulk Columbus will make whatever you want and very frequently does (KVA can too but I dunno how many have taken them up on that yet)

[blasdelf]

Something else atmo.

I agree, and it appears KVA themselves do too: Tubing Info | KVA Stainless

Vibration damping is a phrase heard a lot in the cycling world, but its importance is exaggerated. The term refers to a material's tendency to absorb and dissipate vibrations after some force causes it to start vibrating. Wind chimes produce sustained vibration, pleasing their owners but often annoying the neighbors. Vibration is the result of high-frequency flex or applied loads. The flex of a component is influenced by the material it is made with, its size, and its shape.

The entire discussion of vibration damping is somewhat academic when it comes to cycling, however, since bicycle parts are not suspended in the air like a tuning fork. A bicycle is composed of multiple components, including the frame, the fork, rubber tires. Most importantly, a bicycle is in contact with the ground and it supports a rider whose body absorbs vibrations of the frame.

[Alistair]

I agree, and it appears KVA themselves do too: Tubing Info | KVA Stainless

Fred, good link. KVA's point about the complicating effect of the bike touching the road, and the different frequency responses of all the components connected to the frame, is a good one but after the passage you quoted, they also go on to say this,

"Having said this, the bulk material properties can be used to generalize the "feel" of a frame and its tendency to damp vibrations. Carbon fiber, being very stiff (with a high elastic modulus) is considered by many to be harsh, transmitting every bump and ripple directly to the rider – causing fatigue and discomfort after long rides. Aluminum, magnesium and even titanium have been described as "soft and mushy", with their lower elastic modulus and stiffness. Riders enjoy the feel of steel and stainless steel – the resiliency and liveliness of the material is without comparison."

so they are saying that the frames material does influence ride quality, it's just that it's trickier to define because of the muddling effect of all the other elements that comprise the complete bicycle.

Alistair.

[e-RICHIE]

...so they are saying that the frames material does influence ride quality, it's just that it's trickier to define because of the muddling effect of all the other elements that comprise the complete bicycle.

Alistair.

Having we always been saying this? It's not trickier to define though - the math is there. But
saying you can feel it? That's where I call folks out on this subject. Ergo, my post 17 above.

[Alistair]

Having we always been saying this?

Richard, yeah, good point. I actually almost added words to that effect to my post.

it's not trickier to define though - the math is there. But
saying you can feel it? That's where I call folks out on this subject. Ergo, my post 17 above.

When I say trickier to define I meant that from a maths and engineering pov the complexity of the problem increases greatly when considering the cumulative effect of the system as a whole. I say this with regard to my limited experience in making such calculations. My years as an undergrad, the last time I was studying this type of thing, were some years ago.

I know that there have been some efforts over the years to test whether a rider can accurately identify the type of tubing their bicycle frame is made from. The most recent I can think of was a collaborative effort between Jeff Lyon, Hank Folson and the testers at Bicycle Quarterly. I'll have to dig that issue out and re-read the specifics.

For myself, I could give a crap about the specific dia./wall thickness of the tubing in my frame. I'm interested in the resultant cumulative effect of the whole, and how it rides as a bicycle.

I will say though that over time, it seems natural for a rider, especially a framebuilding rider, to notice patterns in the correlation between bikes that have certain ride qualities, and the spec's of the tubing that were used in building them. Trying to understand and quantify this relationship, whether it be by using mathematics, words or some other means, so as to be able to duplicate ride qualities that are desirable (in future builds), seems like a very normal thing to do, and to want to do (see also Sailboat makers, Samurai sword makers, Race car builders, Gunsmiths etc. etc.).

Obviously, this kind of refining and quantifying has been going on since Starley came up with the safety bicycle. That today there is still debate about how exactly how the different structural elements of a bicycle effect the ultimate feel of how it rides highlights (to me anyway) the difficulty of the task.

Anyway, where were we? Can human beings detect differences in frame tubing? I know a few cyclists who say that they can, and that it matters to them. Does that prove anything? No. Just saying that some people have their (quite strong in some cases) preferences and I feel this is not something that should not be ignored.


Alistair.