ksyrium trash talking?

rudycyclist said:

Other than the fact that Ksyriums are indestructable, I've heard the same things as posted above. Good training wheels but nothing more.

Indestructable, eh? Then how do you explain the several cracked ksyriums that I have seen...?

Don't talk to David Millar about Mavic after last night's TT.

caferacerwanabe said:

Don't talk to David Millar about Mavic after last night's TT.

- hi. What happened ? I read that his rear wheel 'disintegrated'.

.

pistole said:

- hi. What happened ? I read that his rear wheel 'disintegrated'.

.

He went through not one but two rear wheels in the first 300 meters or so.

Ah it was great. The carbon separated perfectly from the alloy part of the disc.

What Mavic is good for: 'pose' value

[img]timesonline.co.ukPen10 185765a.jpgOpen ↗[/img]Thank you Vicky

caferacerwanabe said:

What Mavic is good for: 'pose' value

[img]timesonline.co.ukPen10 185765a.jpgOpen ↗[/img]Thank you Vicky

Very nice. A very nice pre-ride present.

Dietmar said:

In simple terms, the lateral wheel deflection is due to spokes extending and shortening. To first order, that ``silly'' spring constant of the spokes is all that matters, apart from the bending of the rim itself.

Ah, I see the problem now. Your model is that the spokes lengthen and contract upon a change in lateral force to the rim? It is this change in tension that causes the structure to not collapse?

I can help show you why you're wrong. Instead of getting into the technical details, this one lends itself to a quick gedanken experiment. I'll follow it up with a few extra technical points, which should clarify the dynamics of the structure.

Imagine a bicycle wheel. The spoke is anchored quite securely at the rim and hub, no? It is not free to move in any way that is independent of the rim and hub. The spokes may as well be welded in place after they have been tensioned. The spokes are all under tension and the structure is nice and stable. Now, let's put a small sideways force on the rim.

The rim deflects ~1.5 mm sideways. This means, because the ends of the spoke are anchored, that the part of the spoke that is at the rim has also moved ~1.5 mm. The part at the hub did not move at all. It should be a bit more clear now that the spoke did not get stretched 1.5 mm upwards, or contract in any way (in fact this amount of stretch would certainly yield the spoke!). Rather, the spoke was *bent* about 1.5 mm to the side.

You're right that the motion of deflection was not entirely perpendicular to the spokes major axis and that there will be an attendant change in tension. But this is clearly not the mechanism that causes the structure to remain stable. In total, the correct model for the lateral stiffness of a wire spoked wheel is to consider the bending moment of each of the structure elements (spokes, rim and possibly hub flange).

If you're interested, I can also explain why a structure under a radial load is simultaneously under tension and compression. It also helps explain why the modulus of a material is much more related to the shear strength than the yield strength.

John Swanson
www.bikephysics.com

ScienceIsCool said:

Ah, I see the problem now. Your model is that the spokes lengthen and contract upon a change in lateral force to the rim? It is this change in tension that causes the structure to not collapse?

Exactly, this is how a bicycle wheel is designed. That's not my model, by the way; it's the common understanding of how a bicycle wheel gets its stability. Have you looked up what a tensegrity structure is by now? A bicycle wheel is one of the paradigmatic examples of one.

Quoted post said:

I can help show you why you're wrong. Instead of getting into the technical details, this one lends itself to a quick gedanken experiment.

I would strongly advise you to go into the technical details, rather than getting lost in the fantasies you call "gedankenexperiment".

Quoted post said:

The rim deflects ~1.5 mm sideways. This means, because the ends of the spoke are anchored, that the part of the spoke that is at the rim has also moved ~1.5 mm. The part at the hub did not move at all. It should be a bit more clear now that the spoke did not get stretched 1.5 mm upwards, or contract in any way (in fact this amount of stretch would certainly yield the spoke!).

Complete nonsense. As you mention below, the motion you describe is almost normal to the spoke, thus the amount of stretch of the spoke is much, much less than those 1.5mm. If the angle of the spoke with the horizontal is \alpha and the vertical deflection is \delta y, then the spoke will be stretched approximately by \alpha*\delta y, since we can linearize the sine for the small angles involved.

Quoted post said:

Rather, the spoke was *bent* about 1.5 mm to the side.

O.k., here is a little piece of homework for you: Why don't you calculate the bending moment that is necessary to bend your spoke such that the end deflects by 1.5mm. Now figure out the force at the end of the spoke that creates this moment, and then compare that to the actual force that is necessary to make the wheel deflect by 1.5mm. I promise you'll learn something from this exercise. Come back once you have the results.

While you are at it, here's another little piece of homework for you: Why don't you design a bicycle wheel with a hub of zero width, and let me know how its lateral stiffness compares with a standard bicycle wheel. Please do let us know if there are any differences, and what causes those differences, if any. You do understand that for this hypothetical (and obviously useless) wheel, the "bending" of the spokes would be almost exactly the same as the one for a real wheel, right?

Quoted post said:

But this is clearly not the mechanism that causes the structure to remain stable.

You are completely wrong about this, as even a cursory glance at the literature, or at least a minimal understanding of the mechanics and kinematics of this problem would prove.

Quoted post said:

If you're interested, I can also explain why a structure under a radial load is simultaneously under tension and compression.

Honey, I have been teaching this subject both in undergraduate as well as graduate courses for about 15 years. I can put together a finite element model that shows the detailed force and strain distributions in a bicycle wheel to any level of detail you want. I certainly don't need any of your "explanations" to learn something about a structure as classical as a bicycle wheel, let alone listen to your confused musings about a "structure under radial load".

P.S.: Oh, and do let us know how you would true a bicycle wheel. Do you true it by bending the spokes, or do you think it might be a good idea to adjust the spoke tension? 😉

Dietmar said:

I would strongly advise you to go into the technical details, rather than getting lost in the fantasies you call "gedankenexperiment".

gedanken experiments, though I have an extremely limited knowledge, have helped to procure some important physical constants and theories. Instead of a physical experiment, this is a mental experiment, but you appear to be too caught up in an argument.

Nice. You chose to whip out your credentials rather than elucidate... always the sign of a strong technical argument and a full understanding.

Your entire hypothesis and model is nullefied by the test data which shows that lateral stiffness changes with spoke thickness, but not spoke tension even as the spokes get close to zero tension. And yes, the hub width changes the stiffness of a wheel, for the same reason that a truss is stiffer than a beam. Yes, spoke tension is required for structural integrity due to radial loading (otherwise the spokes will go into compression and buckle). Not side loading.

John Swanson
www.bikephysics.com

ScienceIsCool said:

You chose to whip out your credentials rather than elucidate...

Come again? I am sorry, but you are getting a bit disingenious here. Assuming that you do have some reading comprehension, you must have noticed the context in which I made my remark, which was solely as a way to tell you that I do not need your, hmm, "explanations". Other than that, I gave you a whole series of elucidating pointers, which you obviously choose to ignore. Why is that?

Quoted post said:

Your entire hypothesis and model is nullefied by the test data which shows that lateral stiffness changes with spoke thickness, but not spoke tension even as the spokes get close to zero tension.

More nonsense. You clearly have no understanding of the mechanics of this problem whatsoever. The observations you mention above are exactly what one would predict based on what I said. Spoke tension will not affect wheel stiffness simply because the system is in the area of linear elasticity. Anybody who knows anything at all about mechanics and basic math would immediately conclude that spoke tension will have no effect. Like I said, this is in stark contrast to the case of a tensioned spoke subject to bending loads. In that situation you would obviously have enhanced lateral stiffness for higher spoke tension, due to the adverse bending moment created by the tensile forces.

Otherwise, since you clearly refuse to be educated on this subject, there is no point in continuing this debate.

P.S.: If you need even more "elucidation", you might want to study the FE analyses presented here and here. You should pay particular attention to the way the spokes are modelled: As elements that do not carry any moments. If you study these articles carefully, you should be able to get some understanding of the mechanics of this problem. Pay particular attention to what the first author says about linear superposition, in case you still have trouble understanding the effect, or rather non-effect, of spoke tension.

Dietmar said:

P.S.: If you need even more "elucidation", you might want to study the FE analyses presented here and here. You should pay particular attention to the way the spokes are modelled: As elements that do not carry any moments.

As a recovering mechanical engineer, I love talking aobut the science, but at the end of the day, "the proof of the pudding is in the eating". I would rather see debates about a valid experiment (e.g., appropriate method and amount of loading) to determine emperically the product performance. Talk all you want about the mechanics and FEA, but at the end of the day, if you have the real product, measure it! I like that the Scienceiscool is trying to do that.

Finally, as an aside, I am still perplexed that bike magazines do not try to measure bike performance. Reviews are "stiff, comfortable,..." but I would prefer to see an inclusion of numerical test results. Given that the magazines have been reviewing bikes for years, you would think they could have a testing procedure, and improve the procedure as time goes on.

Dietmar said:

Come again? I am sorry, but you are getting a bit disingenious here. Assuming that you do have some reading comprehension, you must have noticed the context in which I made my remark, which was solely as a way to tell you that I do not need your, hmm, "explanations". Other than that, I gave you a whole series of elucidating pointers, which you obviously choose to ignore. Why is that?

More nonsense. You clearly have no understanding of the mechanics of this problem whatsoever. The observations you mention above are exactly what one would predict based on what I said. Spoke tension will not affect wheel stiffness simply because the system is in the area of linear elasticity. Anybody who knows anything at all about mechanics and basic math would immediately conclude that spoke tension will have no effect. Like I said, this is in stark contrast to the case of a tensioned spoke subject to bending loads. In that situation you would obviously have enhanced lateral stiffness for higher spoke tension, due to the adverse bending moment created by the tensile forces.

Otherwise, since you clearly refuse to be educated on this subject, there is no point in continuing this debate.

P.S.: If you need even more "elucidation", you might want to study the FE analyses presented here and here. You should pay particular attention to the way the spokes are modelled: As elements that do not carry any moments. If you study these articles carefully, you should be able to get some understanding of the mechanics of this problem. Pay particular attention to what the first author says about linear superposition, in case you still have trouble understanding the effect, or rather non-effect, of spoke tension.

Both of the FEA you show are for *radial* loading. In which case, yes, it is widely accepted that it is a change in tension (strain) in the spokes and deflection of the rim that provides structural integrity.

A lateral force (one that is parallel to the axis of rotation) on the rim causes the rim and spokes to bend. I.e., a lateral deflection. This moment is what provides structural integrity.

John Swanson
www.bikephysics.com

melslur said:

As a recovering mechanical engineer, I love talking aobut the science, but at the end of the day, "the proof of the pudding is in the eating".

I do not disagree with that.

Quoted post said:

I like that the Scienceiscool is trying to do that.

I agree with that as well, despite my contention that it would benefit him, and his work in that area, if he tried to understand some of the principles of the systems he is measuring. But ultimately, I really couldn't care less if he is or is not interested in the theory.

Quoted post said:

Given that the magazines have been reviewing bikes for years, you would think they could have a testing procedure, and improve the procedure as time goes on.

Ahh, but that assumes that these magazines are anything other than catalogs of product advertisements, held together by the thinnest of glues, of endlessly repeated mostly contentless "technical" articles, and a bit of reporting here and there. Their product reviews, in particular, are mostly useless.

bobbyOCR said:

gedanken experiments, though I have an extremely limited knowledge, have helped to procure some important physical constants and theories. Instead of a physical experiment, this is a mental experiment, but you appear to be too caught up in an argument.

Actually this is how the structure of the benzene ring was discovered. It was in an armchair with a good drink of brandy and a dream!

vascdoc said:

Actually this is how the structure of the benzene ring was discovered. It was in an armchair with a good drink of brandy and a dream!

Not to be misunderstood, there is nothing wrong with a Gedankenexperiment, of course, if it is properly done. The problem with Swanson's "experiment", however, is that it assumes its conclusion, and wrongly so.

A friend of mine just came over with Jobst Brandt's "the Bicycle Wheel", 3rd edition. If anybody is still interested in the issue of how a bicycle wheel supports its load, they may benefit from reading this book. As far as lateral loads are concerned, Brandt's Figure 16 is the one to study...

jhemp_00 said:

I am trying to figure out why so many people are bashing Ksyrium sl and ES wheels? After reading several, supposed scientific wheel test's done that rate the Ksyriums poorly, I am begining to think that these test are flawed, or just fake test done up by other wheel manufacturers!
I have been riding and racing for over 7 years and I have tried all sorts of wheels, from Zipp's to custom wheels. I found the ksyriums were the best feeling wheels I have ever been on, supper stiff, and great acceleration, and I have not had any problems with them. When ever I switch to my spare wheelset (DA hubs, open pro, 32) I immiedatly notice a difference, it's not huge, but the Ksyriums just feel faster. I am sold on the mavics!
I agree, that I am tired of seeing so many of them on the roads, but I think that might be a testiment to how good they are.

As an amateur linguist I'm curious about your usage. Why do you use an apostrophe to make Zipp plural (Zipp's), but not for ksyrium or mavic? For that matter, why is Zipp capitalized while Mavic and Ksyrium are not? Just curious.

OK Dietmar and Science is Cool, My understanding of a spoke is that if the rim deflects sideways the spoke doesn't bend but protrudes further into the rim and looses all tension, this is why the nipples will loosen, because they are under zero load. The wheels that do not do this are R-SYS Mavics and Lightweights, and that is why they are stiffer than 32 spoke wheels even though the spoke tension may be less than the steel spokes. http://www.rouesartisanales.com/article-6833227.html I am not a scientist so do not shoot me down with your scientific language, please. I am just trying to add something.
Back to the original topic, my Ksyrium Elites have been great for the past 5 years but i imediately sold the SL's i got with my new bike. Out here on the flats it is aero all the way!! 🙂

leestevens said:

My understanding of a spoke is that if the rim deflects sideways the spoke doesn't bend but protrudes further into the rim and looses all tension, this is why the nipples will loosen, because they are under zero load.

That's close, but not the whole story. First of all, for small deformations, the spoke on the side towards which you are deforming will lose tension, but usually not all of it. The other part of the story is that the spoke on the opposite side will increase in tension. The resultiung forces are shown in Figure 16 in Brandt's book. The sum of these two effects, plus the resistance to bending of the rim itself, is what creates the stabilizing sideways force. The effect of spoke bending is pretty much negligible, as the little back-of-the-envelope calculation I suggested before will readily show.

leestevens said:

The wheels that do not do this are R-SYS Mavics and Lightweights, and that is why they are stiffer than 32 spoke wheels even though the spoke tension may be less than the steel spokes. rouesartisanales.comarticle 6833227.htmlOpen ↗

Interesting article, by the way, and very relevant to this discussion. However, I have my doubts how important the "very high lateral loads" are in normal use of a bicycle wheel. My understanding was that lateral loads are usually quite small, so the case of the spokes on one side losing tension completely should be rare, although Brandt's figure shows that it indeed does not take much for that to happen.