Lightweight Challenge 700 -> 721.3gr!

Discuss light weight issues concerning road bikes & parts.
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J-Nice
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by J-Nice

520 Dan wrote:J-nice, I think you are probably right on the mavic thing. It seems like they left the door open for multiple models with the lightest, non-adjustable set as the top of the line.


I still don't see the logic behind that rear wheel design. I think that if they were going to commit to such a design they should of realized that they had to go all the way with it, but I am sure by next year they will redesign the rear wheel similar to CS and Lew.

by Weenie


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Mario Jr.
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by Mario Jr.

A rep told me that when Mavic makes the wheel, the dish is wrong. Then they pull the rim towards the non-crankside using the adjustable nipples. That way they can put tension on the rear spokes, witch makes the rearwheel stiffer.

On the frontwheel it nessecary, as the wider bracing angle makes the wheel stiff enough.

To me that sounds logically enough, and when I manhandled the spokes, the rear ones indeed had more tension.

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G man
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by G man

Not been a ww member long, but love it! Love lightweight wheels, ceramic bearings, my bike and cycling. If I see a guy with a dream bike I say "nice bike dude", I don't say, how many kms did you ride last year? I don't race, have a bit of a beer gut and don't have much of a tan. Would I buy a Parlee Z4 with some lightweights tomorrow if I could? You bet I would! Last year while on a ride someone threw a tennis ball in my face out of a car window for being a "poser" on my bike. If only I had some lightweights on my bike, I may have been fast enough to catch him up and give him a good slap!
not quite all the gear; definitely no idea.

GrahamB
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by GrahamB

G man wrote:Last year while on a ride someone threw a tennis ball in my face out of a car window for being a "poser" on my bike.


Or he was just a dick :-( Second ride on my new bike (a Giant, nothing flash) some knob threw an egg at me from a car window. Made a hell of a mess :(
It wasn't a comment on my bike, since it was dark (he switched off the car lights so I couldn't get his rego number) and the street lighting was out.

Maybe the guys with expensive bikes and no tans might just train at night, like me and me ol' mate Floyd :lol:

Lots of people have hobbies based around building nice toys: hi-fi, photography, guns, motorcycles... in most cases there is some tenuous connection to function (ask a hi-fi nut about the unmeasurable benefits of mega-$ bits of wire) but in many cases the tools become and end in themselves. Sure, it can be funny (competitions for who has the loudest car stereo anyone?), but who am I or anyone else to rubbish it? Surely it's no sillier than stamp collecting, as already mentioned. Just so long as no one takes it too seriously... :lol:

Besides, there is a real function: if you're wrapped up in your bike, you'll probably ride it more than if it's an old clunker you can't stand the sight of. I wonder if that gold paint on Bettini's Specialized makes him ride it just a little harder?
Graham

GrahamB
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by GrahamB

Mario Jr. wrote:A rep told me that when Mavic makes the wheel, the dish is wrong. Then they pull the rim towards the non-crankside using the adjustable nipples. That way they can put tension on the rear spokes, witch makes the rearwheel stiffer.


That makes alot of sense. What I've been wondering how much tension the 1-piece wheels (Lightweight, Lew) have on their spokes? They must have some , but it can't be easy to pretension a spoke that has to be glued in place. I can imagine it could be none by bonding all the spokes on one side, then pressing the hub axially to pretension those spokes while fixing the other side...
Graham

alienator
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by alienator

GrahamB wrote:That makes alot of sense. What I've been wondering how much tension the 1-piece wheels (Lightweight, Lew) have on their spokes? They must have some , but it can't be easy to pretension a spoke that has to be glued in place.


LEW wheels aren't one piece, and the spokes are not tensioned. There is nothing, in general, that requires spokes--in all wheel designs--to be pretensioned.

chrism
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by chrism

alienator wrote:LEW wheels aren't one piece, and the spokes are not tensioned. There is nothing, in general, that requires spokes--in all wheel designs--to be pretensioned.

Maybe not, but wheels with spokes which aren't pretensioned are significantly weaker and flexier, since only spokes on one side are contributing to preventing lateral deflection, and NO spokes at all are contributing to supporting the rim vertically under load in the deflection zone at the bottom. By having non pre-tensioned spokes they're basically throwing away most of the engineering in a normal tension spoked wheel.
No scales on the trails

SuperD
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by SuperD

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.

alienator
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by alienator

chrism wrote:Maybe not, but wheels with spokes which aren't pretensioned are significantly weaker and flexier, since only spokes on one side are contributing to preventing lateral deflection, and NO spokes at all are contributing to supporting the rim vertically under load in the deflection zone at the bottom. By having non pre-tensioned spokes they're basically throwing away most of the engineering in a normal tension spoked wheel.


Well, I guess that remains to be seen. Who says you need to tension all wheels? Did you do a trade study to see how the theory plays out with different designs?

Old practices and old ideas are great when you work with old designs. It is entirely possible that new designs don't require the same practices that old designs did. If you'd like examples, all you need to do is look at cars, aircraft, spacecraft, electronics, or anything else designed by men. The take home idea is that you can't necessarily apply what was common wheel building practice to new wheels.

alienator
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by alienator

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.

GrahamB
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by GrahamB

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.


Ok, Alienator has some good points, but let me get technical on just the bit above:
yes, CF spokes can (by using greater CSA for the same weight) have a higher modulus (ie less elongation for the same tension). But it's not infinite!

The reason pre-tensioning works is that in deflecting the wheel, you are not only stretching the spokes on one side, but de-tensioning the other. The result is that you get the same small-deflection modulus as if all the spokes were on the side opposing motion. However this effect ceases as soon as the spokes on one side go slack: Mavic have some nice plots showing this effect, which they use to promote their R-sys wheels.

So, stiffer spokes (in tension) mean you need less pre-tensioning measured as elongation, but the same amount measured as applied force. The only way around this is to have spokes that remain linear through zero... ie the same modulus in compression as tension. That's the point of r-sys. It's unlikely to be true of the Lew/Lightweight/Mavic CCU spokes, since they're flat, although for the Lew & Lightweight versions they are bonded at both ends and would be able to provide some compressive resistance.

It may also be that with carbon spokes (and a very stiff deep-section carbon rim), half of them is enough...

Maybe Carbon Sports or Lew could enlighten us, but it might also be a legitimate piece of IP for them...
Graham

GrahamB
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by GrahamB

alienator wrote:We should keep that in mind on our next rides, after which we proclaim a wheelset super stiff or noodly.



Granted, although if it feels noodly, it probably does matter, by definition...
Graham

alienator
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by alienator

GrahamB wrote:Granted, although if it feels noodly, it probably does matter, by definition...


Yeah, but Mavic found that riders couldn't reliably say what was noodly and what wasn't. I'll assume that riders chosen by Mavic were at least very experienced riders.

GrahamB
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by GrahamB

alienator wrote:Yeah, but Mavic found that riders couldn't reliably say what was noodly and what wasn't.


Interesting. Assuming that a) riders weren't being completely random; and b) they were comparing relative comments by the same rider to avoid one man's noodle being another's... umm... very stiff thing...

... then it would be fascinating to know what is associated to the perception of noodliness.

Here's a tangential issue: if you look at the rolling resistances for tyres, listed as Watts dissipated at 30km/h, the difference between a good clincher and a good tubular is of similar order to the difference between aero's of eg a deep-dish wheel and a Ksyrium... at 50km/h.

So setting aside time trials, the RR should be much more important than aero effects, since riding in a pack at 45-50km/h will generate the RR corresponding to 45-50km/h, but the aero drag of a lower speed because of the bunch effect. The aero drag roughly halves going from 50 -> 30km/h.

Ergo, most of the pro's should be on clinchers most of the time. The fact that they're not, suggests that something else is playing a role, which is presumably bigger than both aero's and RR. Could it be dissipation via flex?
Graham

by Weenie


alienator
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by alienator

GrahamB wrote:Interesting. Assuming that a) riders weren't being completely random; and b) they were comparing relative comments by the same rider to avoid one man's noodle being another's... umm... very stiff thing...

... then it would be fascinating to know what is associated to the perception of noodliness.


The vagaries of human perception. How do you account for the fact that so many people claim that Ksyriums are stiff wheels?

GrahamB wrote:Here's a tangential issue: if you look at the rolling resistances for tyres, listed as Watts dissipated at 30km/h, the difference between a good clincher and a good tubular is of similar order to the difference between aero's of eg a deep-dish wheel and a Ksyrium... at 50km/h.

So setting aside time trials, the RR should be much more important than aero effects, since riding in a pack at 45-50km/h will generate the RR corresponding to 45-50km/h, but the aero drag of a lower speed because of the bunch effect. The aero drag roughly halves going from 50 -> 30km/h.


I think you've over simplified things a bit. You presume a given RR and a given drag, but those things aren't given. Also, it is not conclusive that clinchers in fact have a better RR in all given conditions. So far, the data points that way; however, the data has not necessarily been collected in a way that accounts for varying operating conditions. So, it's a mistake to make that assumption. It is known, however, that aero factors dominate over about 15mph (24kph). Also, you've forgotten that aero drag is quadratic with velocity whereas rolling resistance is only linear. You're assuming that RR overtakes aero at some point in your model, and that cannot be assumed. You need to account for initial conditions, i.e. actual drag numbers, RR numbers, etc.

Ergo, most of the pro's should be on clinchers most of the time. The fact that they're not, suggests that something else is playing a role, which is presumably bigger than both aero's and RR. Could it be dissipation via flex?


IF your assumptions are correct, there is still a lot that is not accounted for. It's doubtful that wheel flex accounts for any significant energy loss at all, given the very tiny amount of frontal deflection any wheel demonstrates. And in a pack, it's unlikely that there's any significant lateral flex. There's really nothing empirical to suggest that a wheel's hysteresis in lateral flex is significant in the pack. The greatest lateral loads are in sprinting, entering a corner, exiting a corner under power, and also in the case where a wheel might hit a large obstruction.

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