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Re: Deflection = power loss (true or false)?
Posted: Tue Aug 27, 2019 7:08 am
by TobinHatesYou
Heine's analogies, as usual, are a little flawed here. His trampoline analogy for example. The reason why the trampoline feels so much more efficient is because the wavelength between jumps increases. You're doing the same work per jump, but you're jumping less often, of course it feels easier. I think most of us agree any power loss is from hysteresis and it's so small it doesn't really matter if you're just reading results from a hub PM and a spider PM.
Biomechanics on the other hand, really hard to qualify. For example I prefer oval rings. It doesn't increase my maximum power, but it results in more comfort in my pedaling dynamics...probably from reduced micro-accelerations. Oval rings would seem to counter Jan's intuition since it makes the "pushback" harder during the peak power phase. Turns out people prefer different things.
Re: Deflection = power loss (true or false)?
Posted: Tue Aug 27, 2019 9:49 am
by wheelsONfire
Ok, it's told fatigue is a crusher when it comes to performance.
Micro vibrations lead to fatigue.
Fatter tires, flex in seatpost/ (some) like saddle.
Bib shorts pads, handlebar tape (and material)
If you didn't feel pain at all, you would keep hammer?
-Yes!
Quantify data as in the pod (link above), not sure i find anything convincing talking fact/data.
It seems it goes back to basics on how people handle muscle fatigue.
Pain in hands, neck, legs, back/ spine
Re: Deflection = power loss (true or false)?
Posted: Tue Aug 27, 2019 9:49 am
by Weenie
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Re: Deflection = power loss (true or false)?
Posted: Mon Sep 09, 2019 10:44 pm
by TheKaiser
C36 wrote: ↑Sun Aug 25, 2019 5:16 pm
Long story short: out of the saddle it does, sitting... I am not sure (we didn’t measured it the same way we did out of the saddle).
The idea that deformation would give energy back seems to ignore that deformation is storing energy on a plan (“laterally”) different than the one used to pedal (“vertically”). One of the clearest illustrations of the phenomenon was the higher power peaks we measured with stiffer wheels. So stiffer resulted in better efficiency (faster for same power) and easier power generation attacking or sprinting.
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I'm inclined to agree with you. "Storage of energy" by lateral flex in a frame doesn't necessarily mean that its returned into drivetrain propulsion. If the frame rebounded before the dead spot in the pedal stroke, in theory then it could spring back against the pedal as pedal loads dropped, and contribute to forward propulsion, but studies on pedaling force and data from dual leg powermeters shows that most people are still exerting max downforce at 4, 5, or even 6 o'clock, even though the vector is no longer aligned with forward propulsion/rotation. I am inclined to think that the frame's lateral deflection will not rebound until the pedals are in the "dead spot" meaning that the frame's rebound will not cause the chain to get any extra "tug" and hence the power is not lost, but also does not contribute to forward propulsion.
From your posts C36, it seems you took part in a study on this topic, but I don't recall seeing mention of what it was or where it was published. Can I get a copy or can you provide a link or something? It has always seemed like at topic that would be viable to study in the lab, but for whatever reason, was being neglected.
Re: Deflection = power loss (true or false)?
Posted: Mon Sep 09, 2019 10:49 pm
by bm0p700f
That's what I was getting at THY, when I wrote less stiff tubes dont necessarily store less energy.
This topic question cant easily be answered but of energy is returned stiffer tubes would show lower hysteria losses. I am not clear though on what the mechanism for converting that stored potential energy into forward kinetic energy. The stored energy goes somewhere.
Re: Deflection = power loss (true or false)?
Posted: Tue Sep 10, 2019 10:37 am
by C36
TheKaiser wrote:
From your posts C36, it seems you took part in a study on this topic, but I don't recall seeing mention of what it was or where it was published. Can I get a copy or can you provide a link or something? It has always seemed like at topic that would be viable to study in the lab, but for whatever reason, was being neglected.
Indeed, was a work done with a major manufacturer some time ago now. Not published and as far as I know, no intention to do so. Sharing the main findings is possible, details or protocol unfortunately not.
It was, back then, a very advanced work with SRM-science and multiple prototypes isolating the different engineering parameters. In short, you could talk about 0.3-0.4kmph difference in 7.5% slope (at around 15kph speed) between flexible and stiff equipment. That’s a combination of the two factors mentioned above (1, gain at constant power and 2,manage to generate more power). At higher power gain will increase.
With power-meters evolutions that improve the measurement during the entire stroke (srm-science could analyse the stroke but was quite difficult to implement) some very interesting work could be done.
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Re: Deflection = power loss (true or false)?
Posted: Fri Sep 13, 2019 5:19 pm
by TheRich
TheKaiser wrote: ↑Mon Sep 09, 2019 10:44 pm
C36 wrote: ↑Sun Aug 25, 2019 5:16 pm
Long story short: out of the saddle it does, sitting... I am not sure (we didn’t measured it the same way we did out of the saddle).
The idea that deformation would give energy back seems to ignore that deformation is storing energy on a plan (“laterally”) different than the one used to pedal (“vertically”). One of the clearest illustrations of the phenomenon was the higher power peaks we measured with stiffer wheels. So stiffer resulted in better efficiency (faster for same power) and easier power generation attacking or sprinting.
Envoyé de mon iPhone en utilisant Tapatalk
I'm inclined to agree with you. "Storage of energy" by lateral flex in a frame doesn't necessarily mean that its returned into drivetrain propulsion. If the frame rebounded before the dead spot in the pedal stroke, in theory then it could spring back against the pedal as pedal loads dropped, and contribute to forward propulsion, but studies on pedaling force and data from dual leg powermeters shows that most people are still exerting max downforce at 4, 5, or even 6 o'clock, even though the vector is no longer aligned with forward propulsion/rotation. I am inclined to think that the frame's lateral deflection will not rebound until the pedals are in the "dead spot" meaning that the frame's rebound will not cause the chain to get any extra "tug" and hence the power is not lost, but also does not contribute to forward propulsion.
From your posts C36, it seems you took part in a study on this topic, but I don't recall seeing mention of what it was or where it was published. Can I get a copy or can you provide a link or something? It has always seemed like at topic that would be viable to study in the lab, but for whatever reason, was being neglected.
A bicycle frame doesn't store energy, it absorbs torque. Since power=torque*velocity, any torque used to flex the frame is not used to produce propulsive work.
Re: Deflection = power loss (true or false)?
Posted: Sat Sep 14, 2019 5:18 am
by sethjs
So people tend to talk about whether frame flex returns as some sort of forward power.
Another issue I once read about is frame flex bringing the wheels out of alignment. Thus creating extra drag. Seemed reasonable to me but I'm not an engineer.
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Re: Deflection = power loss (true or false)?
Posted: Sun Sep 15, 2019 11:56 am
by Valy
sethjs wrote:So people tend to talk about whether frame flex returns as some sort of forward power.
Another issue I once read about is frame flex bringing the wheels out of alignment. Thus creating extra drag. Seemed reasonable to me but I'm not an engineer.
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Actually flex affecting wheel alignment is something I have not thought of before.
I guess it would be tiny as it sits so far away from the BB, but could add to the findings above where stiffer frames have higher speeds.
Another thing I recently realised, is that a less stiff frame aids smoothing out the power delivery - in a similar way that a flywheel smoothes out the engine fluctuations in a car! Also at the power stroke, instead of bumps transferring to your foot / leg as you ride along, a less stiff frame would deflect a bit, further aiding a feeling of connection to the bike.
I have always preferred using my '10 Allez for gaining fitness on. A big part of why, might have been that the frame feels more engaging as it flexes AND it creates a smoother feeling power delivery as you could say at lower fitness, your pedal stroke would have less finesse.
Re: Deflection = power loss (true or false)?
Posted: Mon Sep 16, 2019 5:36 am
by wheelbuilder
sethjs wrote: ↑Sat Sep 14, 2019 5:18 am
So people tend to talk about whether frame flex returns as some sort of forward power.
Another issue I once read about is frame flex bringing the wheels out of alignment. Thus creating extra drag. Seemed reasonable to me but I'm not an engineer.
Sent from my iPhone using Tapatalk
I thought every male over 25 is an engineer now?
Re: Deflection = power loss (true or false)?
Posted: Wed Oct 09, 2019 1:39 pm
by wheelsONfire
Question is if wheels with completely stiff carbon (possibly monocoque) or like Corima MCC, are more prone to cracking as they are so stiff (no give)?
Not sure how ride feel is on wheels like these? I'd love to try Corima MCC 47 WS+, but i guess that will never happen.
Re: Deflection = power loss (true or false)?
Posted: Thu Oct 10, 2019 12:02 am
by bm0p700f
Rim cracking does not appear to due to how stiff the rim is.
Re: Deflection = power loss (true or false)?
Posted: Wed Jun 23, 2021 2:01 pm
by baldheadbiomed
double post delete
Re: Deflection = power loss (true or false)?
Posted: Wed Jun 23, 2021 2:02 pm
by baldheadbiomed
C36 wrote: ↑Tue Sep 10, 2019 10:37 am
Indeed, was a work done with a major manufacturer some time ago now. Not published and as far as I know, no intention to do so. Sharing the main findings is possible, details or protocol unfortunately not.
It was, back then, a very advanced work with SRM-science and multiple prototypes isolating the different engineering parameters. In short, you could talk about 0.3-0.4kmph difference in 7.5% slope (at around 15kph speed) between flexible and stiff equipment. That’s a combination of the two factors mentioned above (1, gain at constant power and 2,manage to generate more power). At higher power gain will increase.
So biking up a 7.5% slope at 15 kmph and I believe you used 300W to get there from another thread? 0.4 kmph gain would be around 9W or 3% more power. If you're a sprinter doing 2000W this goes up to approx 60W gained by the stiffer frame if you scale things linearly and likely even more?
I wonder if you'd gain 3% at 300W from having a stiffer frame you'd gain up to 10% at 2000W as flex is not linear with power - what do you think?
Re: Deflection = power loss (true or false)?
Posted: Thu Jun 24, 2021 11:58 pm
by OnTheRivet
TobinHatesYou wrote: ↑Sun Aug 25, 2019 11:32 pm
There are minimal hysteresis/heat losses. However excessive deflection will change/delay the application of power. Let's assume a system with no deflection...the power you put into the cranks gets transferred directly into forward motion. Now let's imagine the cranks and various tube sections are replaced by springs. Now some of your energy is being stored temporarily in the springs and then released on rebound...but on a delay. This delay might be undesirable, especially in accelerations or other technical situations. In a steady state it wouldn't matter as much.
This^. I had written something similar with regards to hysterisis and you explained it better.
Re: Deflection = power loss (true or false)?
Posted: Sun Jun 27, 2021 8:12 pm
by ghisallo2003
My favourite commentary on the question:
https://www.renehersecycles.com/what-is-planing/
I think deflection and release can be positive or negative depending on cadence, power dynamics, riding style, gradient, and that there is a sweet spot. Too much flex and energy is returned out of cycle, too little and the pedal dynamics become super-critical.
Re: Deflection = power loss (true or false)?
Posted: Sun Jun 27, 2021 8:12 pm
by Weenie
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