ksyrium trash talking?
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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.
No, they really are that bad. Some independent studies like mine confirm what should be easily deduced. Things like, big, fat spokes are bad for aerodynamics. This is intuitively obvious. Aluminum has a very low modulus, hence the wheels with aluminum spokes are not very stiff laterally. Again, this is not strange in any way. They have an average moment of inertia, which really isn't that important anyways. Sum it all up, and... meh. You can get much better performance for much less money.
Some people really like the aesthetics of the wheels. Others believe they are getting a good value. Whatever the reason, if you enjoy your wheels then you have received a good value from them. Just don't try to convince yourself (or others) that they have a real, measureable performance that is comparable to other, better designed wheels such as Shimano's.
John Swanson
www.bikephysics.com
No, they really are that bad. Some independent studies like mine confirm what should be easily deduced. No offense, but I don't trust these studies too much, for a number of reasons.
Aluminum has a very low modulus, hence the wheels with aluminum spokes are not very stiff laterally.One of the reasons is simplistic nonsense like the above.
To wit, yes, the elastic modulus of aluminum is about one third of the one for steel. On the other hand, spokes are typically designed with a cross section determined by yield strength, and the yield strength of aluminum is usually less than one third of the one of steel, with details depending on the precise alloys being used. Now, if we use an aluminmum spoke with a yield strength that is less than one third the one of the steel spoke we are comparing to, then we will end up with a spoke that will be stiffer than the corresponding steel spoke, simply because it will have cross sections that are more than three times larger than the ones of the steel spokes. That is the reason, by the way, why, modulo geometry (mind you, and let's not get into that debate here...), aluminum frames tend to be stiffer than steel frames, elastic modulus notwithstanding.
So, no, it is not at all self-evident that a wheel with aluminum spokes should be less stiff than one with steel spokes. If anything, one would expect exactly the opposite, depending, like I said, on the alloys that are being used.
P.S.: No, I have no idea what the reason for that Ksyrium bashing is. I have never tried those wheels, but my guess is that at the price they are selling, and given their popularity, they can't be all that bad. I usually don't give much currency to the idea that the reason for the success of certain products is that everybody using them is stupid.
I'll agree that the shimanos are great wheels, my wife has a pair and I have secretly taken them out for a few rides and was impressed.
But have you ever ridden on the mavic ksyrium Sl's or ES's?
I'm 185lbs and let me tell you they are VERY laterly stiff, I dont care what your findings or anyone else's state. It is my favorite thing about the wheels, you can stomp on the pedals and get instant feedback. Granted, If I lived someplace flat (Kansas) I would be more interested in a wheel set like the shimanos, ZIPP, or somthing that might have better aero properties. But I ride in the mounains, so the aero aspect is not as important to me.
Other than the fact that Ksyriums are indestructable, I've heard the same things as posted above. Good training wheels but nothing more.
No offense, but I don't trust these studies too much, for a number of reasons.
One of the reasons is simplistic nonsense like the above.
To wit, yes, the elastic modulus of aluminum is about one third of the one for steel. On the other hand, spokes are typically designed with a cross section determined by yield strength, and the yield strength of aluminum is usually less than one third of the one of steel, with details depending on the precise alloys being used. Now, if we use an aluminmum spoke with a yield strength that is less than one third the one of the steel spoke we are comparing to, then we will end up with a spoke that will be stiffer than the corresponding steel spoke, simply because it will have cross sections that are more than three times larger than the ones of the steel spokes. That is the reason, by the way, why, modulo geometry (mind you, and let's not get into that debate here...), aluminum frames tend to be stiffer than steel frames, elastic modulus notwithstanding.
<snip>
I think it would be best if you give some reasons for not trusting these independent studies... I know that I lay it all out for everyone to see. My methods, analysis, equipment, the whole she-bang. The paper I wrote spells it all out for anyone who is interested. I'm even willing to share the raw data with anyone who agrees to not use it for commercial purposes.
Moving on... It's the second moment of inertia that you have to worry about when calculating stiffness. Especially considering that the spoke is not a nice box shape or a cylinder (i.e., helpful symmetries). You combine those with the modulus to get the cross-sectional stiffness. Yield strength values change quite a bit depending on alloy, but modulus values do not. Yield strength has nothing to do with stiffness.
Yes, in order to get an aluminum spoke into the same ballpark as a steel one, it must be many times bigger. Hence, the large non-aerodynamic Ksyrium spokes. No, they are not quite as laterlly stiff as an equivalent steel spoke as borne out by multiple lateral stiffness measurements. Perhaps if they were just a little bit thicker.
Bottom line is that the Ksyrium wheels do not have a performance that matches their price. If you want to argue that, I am willing to defend my numbers with rigorous scientific proof.
John Swanson
www.bikephysics.com
I think it would be best if you give some reasons for not trusting these independent studies... I know that I lay it all out for everyone to see. My methods, analysis, equipment, the whole she-bang. The paper I wrote spells it all out for anyone who is interested. I'm even willing to share the raw data with anyone who agrees to not use it for commercial purposes.
Moving on... It's the second moment of inertia that you have to worry about when calculating stiffness. Especially considering that the spoke is not a nice box shape or a cylinder (i.e., helpful symmetries). You combine those with the modulus to get the cross-sectional stiffness. Yield strength values change quite a bit depending on alloy, but modulus values do not. Yield strength has nothing to do with stiffness.
Yes, in order to get an aluminum spoke into the same ballpark as a steel one, it must be many times bigger. Hence, the large non-aerodynamic Ksyrium spokes. No, they are not quite as laterlly stiff as an equivalent steel spoke as borne out by multiple lateral stiffness measurements. Perhaps if they were just a little bit thicker.
Bottom line is that the Ksyrium wheels do not have a performance that matches their price. If you want to argue that, I am willing to defend my numbers with rigorous scientific proof.
John Swanson
www.bikephysics.com
+1. Very good, as always.
power transfer=product of lacing pattern not spokes, as far as I'm aware.
Lateral stiffness for Ksyriums = crap
weight : price, very average.
They are an average wheelset. Not especially good, but not that bad. If you want a bit of bling for a bit cheaper, you can build your own wheels which have the potential to out perform ksyriums.
So many people have these wheels, but only the people who dislike them bash them. Thus, it seems like everyone hates them.
I think the wheels are great. (I have both the ES and SLs) Very tough and stiff.
I have no complaints.
I think it would be best if you give some reasons for not trusting these independent studies...I gave you one reason: I distrust studies where the author seems to be unaware of some of the fundamental science related to his subject.
Moving on... It's the second moment of inertia that you have to worry about when calculating stiffness. Especially considering that the spoke is not a nice box shape or a cylinder (i.e., helpful symmetries). You combine those with the modulus to get the cross-sectional stiffness. For the case of a standard hub-spoke-rim design this is complete and utter nonsense. As far as the bahavior of such a wheel is concerned, you can regard the spokes as having no inertial moment at all. The spokes are, essentially, under pure tensile stress. The inertial moment you mention is only relevant for bending.
Yield strength has nothing to do with stiffness.I never said it did.
Bottom line is that the Ksyrium wheels do not have a performance that matches their price. If you want to argue that, I am willing to defend my numbers with rigorous scientific proof.Like I said, I have never tried those wheels, so I can't say one way or another. On the other hand, I didn't see any stiffness data on your website. Can you point me to some rigorous results? So far, all we have is assertions, and some anecdotal evidence.
P.S.: Found some data here (http://www.sheldonbrown.com/rinard/wheel/data.htm). It looks like the Mavic Ksyriums (doesn't say what kind, though) are indeed not as stiff as most other wheels.
I gave you one reason: I distrust studies where the author seems to be unaware of some of the fundamental science related to his subject.
For the case of a standard hub-spoke-rim design this is complete and utter nonsense. As far as the bahavior of such a wheel is concerned, you can regard the spokes as having no inertial moment at all. The spokes are, essentially, under pure tensile stress. The inertial moment you mention is only relevant for bending.
First, if you want to attack my understanding of the science that appears in my paper and in my experiment, I encourage you to have it a go. While not peer reviewed, the entire thing was gone over by several scientists (mainly physicists and mech engineers) that I regard highly. I'm no fool and don't want to put anything on the internet with my name attached if it's full of errors. Anyways. Have at 'er, or please accept that my data and conclusions are valid.
Second, is the notion of wheel lateral stiffness. It took me a while to convince myself that the lateal stiffness is not affected by spoke tension. Yes, you are right that the second moment of inertia for the cross-section gives the "bending" moment. This -is- the lateral stiffness of that spoke. I reference a fantastic bit of research which might illuminate the subject a bit better: http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf (http://www.duke.edu/%7Ehpgavin/papers/HPGavin-Wheel-Paper.pdf)
There have also been some experiments which show that lateral stiffness does not vary versus spoke tension until the spoke is almost entirely slack. I'll see if I can dig up the reference, though I'm pretty sure it's also talked about on Sheldon Brown's website.
And lastly, Google is your friend. The lateral stiffness of a front Ksyrium SL wheel is about 50 N/mm. Compared to other wheels, that number is... meh. Not great, but not awful.
John Swanson
www.bikephysics.com
Here is my question,
Will the stiffness rating of a wheel change when tested under actual riding conditions, with the weight of the rider and rotational forces? from what I've seen on the internet, it looks like wheels are placed on a stationary machine that places lateral pressure on the rim and then comes up with a deflection number. I'm just wondering how accurate this method is?
First, if you want to attack my understanding of the science that appears in my paper and in my experiment, I encourage you to have it a go. While not peer reviewed, the entire thing was gone over by several scientists (mainly physicists and mech engineers) that I regard highly. I'm no fool and don't want to put anything on the internet with my name attached if it's full of errors. Anyways. Have at 'er, or please accept that my data and conclusions are valid.
Second, is the notion of wheel lateral stiffness. It took me a while to convince myself that the lateal stiffness is not affected by spoke tension. Yes, you are right that the second moment of inertia for the cross-section gives the "bending" moment. This -is- the lateral stiffness of that spoke. I reference a fantastic bit of research which might illuminate the subject a bit better: http://www.duke.edu/~hpgavin/papers/HPGavin-Wheel-Paper.pdf
There have also been some experiments which show that lateral stiffness does not vary versus spoke tension until the spoke is almost entirely slack. I'll see if I can dig up the reference, though I'm pretty sure it's also talked about on Sheldon Brown's website.
And lastly, Google is your friend. The lateral stiffness of a front Ksyrium SL wheel is about 50 N/mm. Compared to other wheels, that number is... meh. Not great, but not awful.
John Swanson
www.bikephysics.com (http://www.bikephysics.com/)
First, if you want to attack my understanding of the science that appears in my paper and in my experiment, I encourage you to have it a go.
Sigh... I thought I have made clear, twice now, what statements of yours I criticize. Feel free to re-read my last two posts.
But anyway, since you asked regarding the measurements you talk about in your piece on the web, the bearing friction data are dicey, unless optimal adjustment of the bearings is tightly controlled for. One may also ask how representative measurements under no-load conditions are to the practically relevant case of the bearings under vertical load.
For the aerodynamics, you should test the wheels with indentical tires mounted on them, otherwise your results will be affected by parts of the rim that are not exposed in practical use. I don't know if any of your wheels still used that design, but if you have exposed nipples on the inside of the rim, that will increase aerodynamic drag.
Second, is the notion of wheel lateral stiffness. It took me a while to convince myself that the lateal stiffness is not affected by spoke tension.
That is an entirely obvious result. Wheel stiffness, as far as spoke effects are concerned (let's not forget that the rim itself plays a big role, too), depends on the spring constant of the spoke (an average of the elastic modulus times the cross section over the length of the spoke). Simply put it depends on how much the spoke extends for a given force. This clearly is completely independent of spoke tension.
This -is- the lateral stiffness of that spoke.
Once again, the "lateral stiffness" (I assume you mean bending stiffness) of the spoke is irrelevant, and has nothing to do with the lateral stiffness of the wheel. The spoke does not bend under any reasonable load of the wheel.
I'm pretty sure you didn't bother to read the reference I gave... You should go take a look.
I think there are some flaws in your understanding of "bending". Placing a radial load on any structure will cause a lateral deflection. Parts of the structure will be under tension and some under compression dependent on the shape of the structure and how the load is oriented.
To determine the amount of lateral deflection under radial load, it is important to know the cross-sectional shape (i.e., second moment of inertia) and the modulus. No spring constants or silly things like that.
When you place a load on the rim of a wheel such that it is perpendicular to the primary plane, you are placing (to within a few degrees) a radial load on the supporting spokes. Yes, you are also placing a radial load on the rim itself. How much each element (and the wheel as a whole) deflects depends on the stiffness which is determined by the second moment of inertia and modulus. Again, go check out the reference I gave. The guy really did his homework and built a beautiful theoretical model. His experimental data fit perfectly. Awesome.
And yes, you point out a valid criticism of measuring bearing performance without preload. I discuss this in my paper as one of the short-comings of my method. I do think that it does provide a valuable point of relative comparison, though.
As for the aerodynamics, no I do not think testing with a tire will improve the results. There are several reasons for this which I don't want to bother with here. This thread has already been hi-jacked and the posts are getting long and tedious. I'm also not concerned about exposed spoke holes. Again, I will omit the long and tedious answers. I will say, however, that those are very valid areas of concern and that you are very right to question them.
I think I'm done with this thread since I'm not really contributing anything any more other than decending into increasingly pedantic arguments with someone I don't know. I feel that my initial claims still hold, both on a theoretical basis and with real world experimental results. Ksyrium wheels do not have a performance that matches their price. If any of you like your Ksyrium wheels, then that's awesome. I'[m not particularly dogmatic about the whole thing. Ride what makes you happy.
John Swanson
www.bikephysics.com
I think there are some flaws in your understanding of "bending".You would have to point out what those supposed flaws might be.
Placing a radial load on any structure will cause a lateral deflection. Parts of the structure will be under tension and some under compression dependent on the shape of the structure and how the load is oriented.This is just confused, as far as I can tell.
To determine the amount of lateral deflection under radial load, it is important to know the cross-sectional shape (i.e., second moment of inertia) and the modulus. No spring constants or silly things like that.You clearly do not understand the requisite kinematics of how a bicycle wheel bends laterally. Spoke bending plays no relevant role there. Here's a little hint for you: If it did, your result of lateral stiffness being independent of spoke tension would not hold. Think about it.
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.
Again, go check out the reference I gave. I am quite familiar with it. You might want to examine his results a bit more closely. You could also try and find out what a tensegrity structure is, and how that concept relates to bicycle wheels.
Will the stiffness rating of a wheel change when tested under actual riding conditions, with the weight of the rider and rotational forces?
No, those things should not affect the results to any significant degree.
Well, I don't know much about the science behind the wheels, but I've really enjoyed my SL's for the last 6 months. I've used them for TT's, crits, and road races and they are as true as day one. I have to say that I have never ridden and quality set of handbuilts and would be willing if you guys want to dontate them... :)
Well, I don't know much about the science behind the wheels, but I've really enjoyed my SL's for the last 6 months. I've used them for TT's, crits, and road races and they are as true as day one. I have to say that I have never ridden and quality set of handbuilts and would be willing if you guys want to dontate them... :)
And that's one of the points that John made: if you like your stuff, great. That's what counts.
I race on Ksyrium Elites(ok, so I'm going to get some faster wheels for next season!) and have trained on them too. So far they have about 6000kms on them. I weigh about 72kgs. They are as straight(so am I!!:o ) as when I got them(untrued in that time) and I am very happy with them. :)
I test with personal experience, because in the end it's me that will be riding them. Your mileage may vary, but that's why you should test them yourself instead of relying upon lab numbers.
I tried a set of SL's out last year. Bought them used, rode them for a month, resold them for $25 less than what I paid. Sharp looking wheels, I have to say. They reminded me a lot of my Rolf Vector Pro's (a bargain these days, if you're into low spoke/aero rim wheelsets). Very stiff, in fact a bit too stiff for me - the harsh ride really hammered my wrists, even with gloves on. Then again, your wrists may not be as sensitive as mine.
Ended up buying a used set of 404's on ebay. Can't say that I noticed any substantial loss in stiffness, but the very smooth ride was most welcome, and there does seem to be a slight but perceptable advantage when speed rises above 40mph. I love the Zipps. Sweet ride, sweet handling, and you can really do a Falco on the downhills. Psychs out some of my riding buddies, too. I dropped a couple on a climb last spring, and heard them grumbling about my fancy wheels, without considering that the 404's are no better for climbing than any other wheelset.
So I'm willing to put up with patching tubies (not very often) and watching out for road hazards (the CF rims do call for good judgment there) because they just feel so right. I hate to take them off of the bike.
Again, YMMV. Try them yourself, and see what you think.
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