What is the truth behind bike weight? Does it really help THAT much?

thoughtforfood

Ok, so I don't have any idea what you are talking about.


I do know this, if the flex of the frame caused by pressure at the bottom bracket causes the track of the front and rear tires to change (and it does), then the contact patch for the tires increases because of their turn, however slight, from the direction of your travel. This increases resistance and therefore causes a loss of energy. It might be slight, but in just that, it is present, and therefore a stiffer frame is less efficient in producing forward momentum.


That is totally unscientific however, though you could replicate that very easily. You don't need to test whether a larger contact patch causes loss of energy, that has been done. All you should have to show is that the flex of the frame does alter the track of the wheel/tire, and that has been done also. Therefore a more flexible frame causes a loss of energy.


Am I missing something?

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Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.
-- Albert Einstein

alienator

I just return condescension when condescension is distributed re: bike properties and how what properties affect what. So? Is there something intrinsically wrong with questioning because of a lack of data? Hey, I done did the analysis, and the dark, evil losses due to frame noodlism just ain't there. Sorry.

I think condescension is much more appetizing than blindly swallowing marketing spiel. Besides, condescension serves well the crowd around here.

Sorry, Cupcake.

thoughtforfood

Ok sweetie, show your data. I mean, such an obvious mental giant like yourself should understand that when you at one point ask for data showing a finding contrary to your own, revealing your data is a logical thing to do. Put up or shut up I always say. I mean since you "done did the analysis," show your data there fuckwit.

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Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.
-- Albert Einstein

thoughtforfood

Actually, even without a larger contact patch, you still lose energy because of the manner in which a round object reacts to altering its pitch in relation to its line of travel. You are gonna lose energy, no way around it.

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Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.
-- Albert Einstein

Crankyfeet

And don't use a random insertion of Bayes Theorem again...

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alienator

The point is, what amount of energy is lost? Is it significant to the system in question? Is the energy lost greater in magnitude than the noise in the system?

The idea that something has to be lost is a bit too simplistic. Of course, by the second law of thermodynamics, something has to be lost; however just because something is lost doesn't mean that the system responds in any noticeable way to that loss.

John's point and the point of all the analysis ever done on this, uhm, point, is that the losses are statistically insignificant and are lost in the noise. Moreover, if you create a model wherein the system is perturbed so much that there are significant losses, then that perturbation will exist even for stiff systems. Example: if you model a 350lb rider with a cadence so bad that the force applied to the pedals is applied at a 60 degree angle to the bike plane's normal, the energy applied to BB, normal to the bike's plane will be the same whether the bike is made of pot metal, CF, or Inconel X. The frequencies at which the frames respond might be different, but the energies won't change.

Measuring frame deflection doesn't really tell you anything instructive. It'll only verify that stiffer frames, i.e. frames with higher effective spring constants, deflect less for a given force input. It'll also only show that a given energy, U, put into frame one is the same as put into frame two. That doesn't change. Differing spring constants don't limit the amount of energy put into a system.

sogood

Is that an academic jargon commonly used during scientific discussions?

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artemidorus

He is assuming for purposes of simplicity that ALL the energy going into deforming the frame is lost, ie that it does work heating the frame. In fact, and this has already been discussed, it is likely that some/most of the stored energy in the deformed frame goes back into doing the work of turning the cranks, so John's model calculates worst case losses.
One feature of frame deformation that was not included in the model, however, is the effect of a turning bias on the rear wheel. Whether this could do extra waste work in a slight sideways scrubbing of the tyre, or whether subtle matching turns of the front wheel prevent this wastage, I don't know.

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alienator

Again, that's a given. The point is that the energy lost is very small. Of course energy is lost: that's the whole point of S=k*Ln(ω). Τhere is no such thing as a free lunch. The energy losses in bike systems are very small over all. Logically, then, the losses when examined individually, are much smaller. It's difficult for people to even reliably sense the big losses in bike systems: aero losses, losses due to rolling resistance, and etc.

artemidorus

His entire model assumes that all the frame deforming energy is "damped" rather than being returned to the cranks in contributing to useful work.

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"All that we see and seem is but a dream, within a dream..."

thoughtforfood

Then, taking my point into account, altering the pitch of the tires to a greater extent will cause a greater loss of energy. The more perpendicular to the line of travel, the greater the loss of energy. Is it just noise? If you were cycling 10 miles in a sprint it might make a measurable difference, otherwise, probably very little. However, that was not the assertion. Your assertion was that "evil losses due to frame noodlism just ain't there." Well, maybe we can determine what constitutes "evil," but it sounds to me as though you were suggesting that it is non-existent. Then you say that it is there.

I would also suggest that two equal sprinters, one on a stiff bike, and one on a noodle, would necssitate an outcome that favored the rider on the stiff bike every time. That is measurable.

Maybe making a clear point, and not demeaning someone in doing so would be a better option for you.

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Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.
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thoughtforfood

No, it is a term of endearment I use with my closest homies.

__________________
Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.
-- Albert Einstein

alienator

It ain't there=it's lost in the noise and is of so very little consequence that your ass can't measure it, that your ass can't reliably say that it has any effect at all, that by being lost in the noise, it's not worth thinking about.

The point was clear. Whether you felt demeaned or not really doesn't matter to me. I mean, I could really care less.

Your sprinter experiment....well, have at it Toodles, and let us know what results your experimental accumen comes up with. I'll bet big money that again, the difference is lost in the noise. I'll bet by the time you get around to quantifying--if you're even capable of it--all of the different variables that will influence your data, that you'll find you won't be able to discern a measureable difference.

Have at it.

Let us know when you publish your paper.

Crankyfeet

So now you are privy to all the proprietary analysis ever done on this? That's a very bold statement to make. I'd like to know who has undertaken tests, apart from John here. With no disrespect to John intended, I am not convinced that the "x" values given by manufacturer's are the "x' values for the frame material and truss given the forces being applied to the bottom bracket. Torsional deflection of a truss has a lot to do with the truss and joint design IMO as well as the material. But if you think that the deflection, or material is irrelevant, then go for a sprint on a PVC tube frame, and see if you perform the same.

So where is your data, since you cite here that you have seen "all the analysis ever done"? Let's face it alienator: you start with a mindset opinion (eg. Expensive frames are over-hyped), then you just BS around, trying to sound academic, dropping a completely irrelevant equation every now and then, telling us that you "done did the analysis" and the above quote of having seen all the analyses ever done, asking for people to show their data when it doesn't agree with your viewpoint, then seeming to lie that you have data yourself (where is it??), and not showing us anything (picture: alienator feverishly private messaging John Swanson to send him some of his calcs).

I'm prepared to admit I'm wrong. I don't have any data, other than trying to work out the system in my head and the opinion of pro cyclists (and amateurs as well) garnered from their experience. But I have never claimed to have any data. You have. If I could just be convinced by your big talk about the data, and that you do have any credible data (after all, data is only as good as the test or model that produces it in any case).

I also know that energy is lost and that it is not necessarily redelivered back into the system with "springback" (if it springs back when the pedals at 12 and 6 o'clock, then there will be nada return of energy to the drivetrain). The question here is magnitude (however any amount of loss is a concern, and it always goes in one direction, unlike noise which is random). So far we have just been feasted with platitudes to back up your thesis that stiffness is a non-factor to the performance of a sprinter at the money end of a race.

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