ksyrium trash talking? - Page 2

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...

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!! ) 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.

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.

- 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.

__________________
BMC SL01
SRAM Force


thank you crank n' cycles...If you are ever in SW WA, take a trip to Crank N' Cycles.

What Mavic is good for: 'pose' value

Thank you Vicky

Very nice. A very nice pre-ride present.

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

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.

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

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.

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?

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.

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?

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.

__________________
BMC SL01
SRAM Force


thank you crank n' cycles...If you are ever in SW WA, take a trip to Crank N' Cycles.