No scientific answer but it does always remind me of the sound of the Tardis when one of them whooshes by.

Cheers me up at least and also cheers me up to know that some people spend a fortune on their bike, but they still can't swim.

So we can't blink now either?

Some high efficiency speakers will get you 101db at 1m with 1W. Six db increase would require four times as much power in the less efficient speakers.

This proves that loud wheels are faster as they are just more efficient making more noise with same power.

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It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

- does the sound come from the carbon skins vibrating to act like a giant speaker?
- how much energy does it cost to make that sound? is it even significant?
- does that sound translate into rolling resistance of a wheel?
- would the wheel be a little faster/efficient if there was a core or integral struts that stopped the vibrations?

The disc isn't losing power just because it is generating noise. Rather it is efficient at turning vibration into sound. There are good reasons to reduce vibration that is caused by interactions between the bike and road, but once it has been imparted to the system, I don't think there is a anything gained by damping it or turning it into a less noisy form or frequency.

Thank you for answering the question in a way that was helpful to the OP and myself. I hadn't thought much about this and your answer cleared it up nicely.

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AndyF
bike geek

Although I don't disagree that the sound energy is very small, It's not appropriate to use force vectors for an argument against damping losses. Consider an extreme example of an oil-filled cannister with a mass that can only move vertically. The energy that is dissipated into the oil as heat comes from the rider, and if you write out a conservation of energy equation you'll see that for a given rider power, less is available for kinetic energy.

This is similar to crr losses, as some of the energy used to deform a tire carcass is not returned to the road. And in a sense, this should give a good intuitive baseline for some upper limit of wheel vibration losses, since we have some grasp of how much efficiency is lost from very flexible rubber facing more extreme local deformations relative to the magnitude of the vibrations on carbon wheels.

As some food for thought, the sloshing and shaking of the rider's body mass is likely a lot lossier than stiff carbon wheels oscillating in their linear range (without permanently deforming), even though you don't (or shouldn't!) hear it.

Yes, but if you harness all those blinks over the course of 180km you might see some real gains!

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Long Chile was a silly place.

The original question is very interesting. Vibration could possibly affect CRR, if it was in the correct plane such that it increased the amplitude of the deflection of the hub center with respect to the road surface. In that case, more or less deflection of the tire side wall is occurring, which changes the amount of heat energy lost to the system from hysteresis. I think it more likely that a disk surface is acting as a speaker cone of sorts. If there is vibration normal to the plane of the wheel, then the interaction with the airflow needs to be accounted for. The hysteresis loss in the disk surface means the airflow is imparting energy, which might mean increased drag, but it could also be that the vibration affects flow attachment in an advantageous way much like the drag of vortex generators or trip surfaces yield an overall reduction in drag because the airflow over the entire surface is reduced due to less turbulence downstream. My gut says the effect either way is tiny, but no way to know without testing CRR and drag.

As I said earlier, much more a 2nd Law problem than 1st Law.

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Brian

Gonna buy a fast car, put on my lead boots, take a long, long drive
I may end up spending all my money, but I'll still be alive

Thanks

I like how this non weightbearing and short axis CD looks fluid at high speed
https://www.youtube.com/watch?v=zs7x1Hu29Wc

I couldnt find anything on bike spokes or discs

This question has nothing to do with newton laws. This is thermodynamics. First law. Conservation of energy.

Like someone said, yes of course it takes energy to create sound, but a sound quite loud to our ears requires a miniscule amount of energy from bike's drivetrain. Much less than 1W to make that creaking noise, or whatever noise you are hearing.

So I couldnt apply Newton law one - where the external force is negative through sound generation?

That depends on the efficiency of sound creation. But I think the assumption is here that the walls of a disc probably approach the ideal speaker cone design, so are probably incredibly efficient, and very low-energy displacement from vibration results in big noise.

The sound is what happens right before one reaches Ludicrous Speed!

If I had one wish as a broadcast engineer with a degree in audio and acoustics, it would be that people would stop saying "dB" without quoting the standard reference value. A dB without its reference value is simply a ratio. Kills me.

I guess you meant 101 dB ref 10^-12 watts, or more likely because you said at 1m you might have meant dB SPL relative to 20uPa.

Nerd goes back in his box.

Oh, and to the guy who said this



Not the same thing at all, not even close. Read about entropy and the efficiency of energy transducers.

So much bad science on here.

I thought the OP was a reasonable question. Whatever form the waste energy ends up being in - acoustic or heat - it is still waste energy and indicative of losses in the system. The question is, are these additional losses or would they otherwise manifest in some other way in another, quieter, wheel... eg as heat. Not necessarily, I don't think. Imagine a really really wobbly wheel that makes the rider bob up and down and throws energy away willy nilly vs a simple stiff spoked wheel. One is wasting more energy than the other because there is a degree of freedom or a vibration taking place that would otherwise not be. Now imagine that it is just a small vibration that is manifest acoustically. Could still be a difference in the system loss vs a wheel that doesn't vibrate the same way, even if it is just small. I kind of think if it was affecting anything at all it would be the "power to spin" part of the system, and maybe it loses something vs another wheel. But then it gains in other ways, and on balance it is worth it I'm sure. I thought it was a good question.

As somebody else said, unless you have a perfectly efficient acoustic-mechanical transducer (doesn't exist) then it costs more mechanical watts in the drive train than you get acoustic watts in the air. For example, a well designed electroacoustic transducer (ie a loudspeaker) might have a sensitivity north of 90dB (no reference needed, this IS a ratio!) or efficiency around 2-3%. BUT, the actual values being considered are tiny. A single watt of acoustic power is the Sound Power Level equivalent of a heavy thunderstorm or a symphony orchestra. A hairdryer, for example, represents about 10^-6 watts.

So in summary, a good question but don't fret it.

I have a bass cabinet and amplifier that will "blow the balls off a charging rhino at 50 paces" to quote a well know hard rocker. It plugs into a standard 15 amp outlet and puts out 1000 watts RMS. I could literally replicate the Memorex commercial with it. I have never blown a fuse at any venue I've played, and I've played in some seriously sketching places.

I doubt if anything on your bike can produce 1/100th of the sound I can in a big venue, so the answer is "yes it takes power, but in the grand theme of things, not a measurable amount."

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"...the street finds its own uses for things"

Can I coat my frame in a piezoelectric film and use it to charge a Di2 battery? May as well do something with that vibration.

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Pactimo brand ambassador, ask me about promo codes

Ok box nerd. But as a fan of home audio loudspeakers I often see them rated as I stated, e.g.:

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It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

Don't even get me started on 1w at 1m. The actual international standard for sensitivity is based on 2.83v input (RMS not peak) at 1m, which for an 8 ohm impedance represents 1w input. But speaker impedances vary and some companies choose to state it as 1w input and then unfairly normalise the voltage to account for the impedance at the testing frequency. Why unfair? The amplifier is having to deliver higher voltage. Similarly if they stick to 2.83v with a lower impedance speaker it will draw more power from the amp, also unfair. So it isn't an apples for apples comparison. Which is why they should state impedance, a bit like bike companies should state yaw angles.

In that value, it should read dB SPL to reference the RMS pressure to 20uPa (human minimum hearing threshold), but the lazy sods never bother. Which is fine because it is "standard", and not as heinous as massaging the impedance of the system to inflate the sensitivity level that they can publish. A bit like using shit yaw angles to let you publish low grammes of drag.

I fairness I didn't really have anything to complain about other than a pet peeve that always bothers me. You should see the irresponsible use of the dB in broadcasting, even worse. But I finally found a topic on here I know something about.

Ok that makes sense to me (a little). Do you listen to music? If so, what is you main home setup? (We are deraileuring this thread, but I'm not sure it is making anyone faster.)

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It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

Lots of wheels lose unspecified quantities of watts by flexing (this is your vector going not quite where you would really like it to). Mostly it will go as heat by hysteresis, disc wheels are more efficient at generating sound as they flex (this just transfers the ultimate hysteresis to the air), I doubt they are losing more energy in total than trispoke / deep rim / old skool. Make your disc heavier and/or stiffer and the noise should decrease, I reckon your mods will cost more energy than they could possibly save.