SuperD wrote:I thought that the carbon fiber spokes have much less elongation than metal spokes (given the same tensile force), therefore they don't need to pre-tensioned to achieve the same result.
If the carbon spokes behaved like metal spokes, and they had no pre-tension, I would agree with chrism in saying such a wheel would be flexy to the point of being unridable. But, since people have ridden these wheels and (to the best of my knowledge) haven't complained about them being super-flexy, either A) there is pretension and Lew is lying to us all or B) the carbon spokes do indeed behave differently than metal spokes and so pre-tension isn't needed for this wheel material/design. I can't see how they could expect to pull off option A, and option B makes perfect sense to me.
The real problem with the discussion re: wheels--and really, any discussion about wheels, frames, and etc.--is that people throw around the word "stiffness" as if it's a given parameter that has to behave in the same way in all forms. This simply isn't true. Really, I doubt many have considered what stiffness means and what an ideal stress/strain curve would like for a frame, wheel, or whatever. There are times when you don't want something so stiff, and other times when you want that something to be pretty stiff. You might want those properties to be linear for a given product, or you might want them to be non-linear. There are relatively few times, I'd wager, when for any bike part you'd want it to be as stiff as possible at any given load.
I think cyclists need to recalibrate their thinking w/ respect to stiffness and consider that it's not sufficient or necessarily good engineering to say that something should just be "stiff" or the "stiffest."
The drive to make the stiffest frames is purely market driven. It's got nothing to do with the effects of stiffness on performance, because no one has yet produced any data whatsoever that correlates frame stiffness with improved performance.
With wheels, it's possible the stiffness needs might be even more complicated. Why not? Wheel aero properties are far more complicated than frame aero properties. As soon as someone produces data that says that wheels must be uber stiff across their entire deflection range, in all riding conditions, then we'll see. Until then, no such data exists. Don't forget that even Mavic has said that the role stiffness plays in wheel performance is rather undefined, and that riders are really bad at determining whether a wheel is stiff or not.
We should keep that in mind on our next rides, after which we proclaim a wheelset super stiff or noodly.