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PostPosted: Tue Nov 15, 2016 9:30 am 
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Marin wrote:
Stiffness is way overrated. Stiffer frames, components or shoes will *not* "increase power transfer", they will just feel different, which some might prefer.

They won't make you any faster though.

Agree about fit being the highest priority.


Whilst I would agree that it's probably overrated, especially for most riders, and that fit is critical, let's not get too carried away.

It's important to have as direct and stiff a line of power transfer as possible, especially for a sprinter, where instant reaction is required.

Imagine repeatedly pushing and pulling a block of steel across a table via a long stiff steel handle. 99.9999% of your work goes into moving the block.

Now insert a mini spring and damper system in the handle. Now a more significant % of your work is lost in said damper, and you have also lost that 'direct connection' feel to the block.

Insoles, gloves, handlebars, bar tape, stem, frame, shoe sole, cranks, wheels, tyres etc. are all not 100% stiff and will all flex slightly under power. Add all these elements up and you can start to get measurable losses, and of course, a 'spongier' feel.

But unless you're competing at the pointy end of things, and knocking out 1000W+, I doubt it's of much concern for most of us.....

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Posted: Tue Nov 15, 2016 9:30 am 


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PostPosted: Tue Nov 15, 2016 9:39 am 
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Only there's no damper in the soles, components and frames - so all the energy is converted into forward motion anyway.

If your soles, cranks or frame are getting warm during use you lose energy, but they aren't so you don't :D


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PostPosted: Tue Nov 15, 2016 9:58 am 
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let's not forget about having confidence in your equipment. At least for me stiffer equipment 'feels' safer so I have more confidence in it and can hence push harder.

Also from my experience, I'd say fit is overrated. Sure if you're top of your game and you need every last marginal gain go for it, but if you're racing 20-120 minute races comfort doesn't really matter. When I first started out I used to ride shoes that were slightly too big for me, and it never really bothered me. For the last two seasons I've had proper fitting shoes (custom fitted shimano R321 for road / Bont A1 for track) but it doesn't really affect my performance on race day (in fact some of my best performances (in placings and power) were with shoes that some can argue are a size too big for me), they're just 'nice' to have. So I'd say if you're racing, within certain fitting boundaries (I don't think the same argument would apply if the shoes were too small, or WAY too big), get the stiffest shoe you can afford.

Just my opinion, feel free to disagree - we all ride for different purposes so it's not surprising there are different takes on this issue.

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PostPosted: Tue Nov 15, 2016 10:14 am 
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Marin wrote:
Only there's no damper in the soles, components and frames - so all the energy is converted into forward motion anyway.

If your soles, cranks or frame are getting warm during use you lose energy, but they aren't so you don't :D


From Wikipedia;
-----
A large damping capacity is desirable for materials used in structures where unwanted vibrations are induced during operation such as machine tool bases or crankshafts. Materials like brass and steel have small damping capacities allowing vibration energy to be transmitted through them without attenuation. An example of a material with a large damping capacity is gray cast iron. [1]

An understanding of this effect can be gained from observation of a stress-strain diagram with exaggerated features. The units of stress are force per unit area, while strain has units of length per length. Any area covered by integrating each instant of a loading and unloading cycle will then be in terms of force times length per volume, which is equivalent to energy per unit volume. This energy represents the amount of mechanical energy being converted to heat in a volume of material resulting in damping.

----

Damping of a structure can be obtained by passive or active methods.

Rubber is commonly used as a damping material due to it's visco-elasticity. The effects of heat loss in tyres due to hysteresis are well known,

Most materials have some kind of measurable spring rate and damping characteristics.

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PostPosted: Tue Nov 15, 2016 11:07 am 
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Exactly, that's why we aren't using rubber in components that are mainly used in power transfer, but materials like brass (in bearings), steel, or carbon fiber or aluminum which also have very little inherent damping.


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PostPosted: Tue Nov 15, 2016 11:36 am 
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Marin wrote:
Exactly, that's why we aren't using rubber in components that are mainly used in power transfer, but materials like brass (in bearings), steel, or carbon fiber or aluminum which also have very little inherent damping.


Very little, yes. But it's there. If you repeatedly stress a component like a carbon bar in a test rig, it will heat up very slightly.

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PostPosted: Tue Nov 15, 2016 9:45 pm 
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Another vote for Bonts, the top-end power increase is uncanny, both in the power data and feel, and immediately noticeable when switching to normal "dress shoe" type road shoes. Normal road shoe I find better for threshold efforts however.

Track and crits: Bonts
Everything else: Standard road shoes


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PostPosted: Wed Nov 16, 2016 1:01 am 
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cyclespeed wrote:
Marin wrote:
Exactly, that's why we aren't using rubber in components that are mainly used in power transfer, but materials like brass (in bearings), steel, or carbon fiber or aluminum which also have very little inherent damping.


Very little, yes. But it's there. If you repeatedly stress a component like a carbon bar in a test rig, it will heat up very slightly.


This is true, but it's true for every material. In fact, infrared cameras are used to study stresses in parts; FLIR makes cameras for just this purpose. Here's an image from a tensile test:

Image

But it's important to remember that the temperature gradients from elastic strain are not just "very slight" but so small they're hard to detect. A good infrared camera will need to distinguish temperature differences of 0.02°C (0.036°F). The energy lost to hysteresis from elastic strain in metals is minuscule; that's why Sean Kelly was able to sprint explosively on flexy Vitus aluminum frames.

Brass and steel both have little inherent damping; it's true. But carbon fiber has quite a bit, which is why carbon frames, bars and seatposts "kill road buzz." They're damping out the high-frequency vibrations we perceive as buzz. Magnesium also has quite a bit of inherent damping.

Overall, though. Marin is dead-on here. No one is losing any substantial power to "flex." If they were, none of us would ride carbon frames; they'd be measurably slower than metal frames.

I feel obligated to point out that "power transfer" and "flex" are terms that have no meaning in engineering terms. Others in this thread have pointed out that there are psychological benefits in feeling directly connected to the bike and road. The first "good" bike I ever test-rode (in 1987) was a Cannondale, and basically every other bike on the road was a lugged steel bike. I couldn't believe how much stiffer it was than my crappy ten-speed. It felt more efficient than the equivalent steel bike I test-rode. But it wasn't more efficient; it was just stiffer.

But there are no road bike frames, bars or shoes that fail to move you down the road effectively because they aren't stiff enough.


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PostPosted: Wed Nov 16, 2016 1:43 am 
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youngs_modulus- who are you? Are you BRM? Are we just wasting our money on marketing BS?


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PostPosted: Wed Nov 16, 2016 1:53 am 
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cyclespeed wrote:
It's important to have as direct and stiff a line of power transfer as possible, especially for a sprinter, where instant reaction is required.

I'm not trying to pile on, cyclespeed. But your comment points to something many people miss: you don't get more power or "faster response" from a stiffer shoe or even a stiffer frame.

bungis wrote:
Another vote for Bonts, the top-end power increase is uncanny, both in the power data and feel <snip>

I don't doubt that you *feel* a lot more powerful, but if you're generating more power with your Bonts, it's because you're pedaling harder when you wear them. (This sort of effect is almost impossible to avoid; that's why double-blind studies are the scientific gold standard).

Most power meter specs list an accuracy on the order of +/- 1.5 percent. Accuracy is not the same thing as precision, of course, but it's not unreasonable to assume that you'd need to make ~2% more power to get a clear increase in the reading from your power meter.

Let's say you sprint at 1200 watts for 10 seconds. So when you put on your Bonts, and pedal that hard, your meter now reads 24 watts higher (1224 W). That means your regular shoes were dissipating at least 12 watts each. That's a lot! It's not power that matters here, but energy. Energy is in units of Joules (for SI) and 1 Joule=1 Watt * 1 second. So in a ten-second sprint, we get a total energy of 120 Joules (10s * 12 W = 120 J).

Carbon composites have a specific heat capacity in the neighborhood of 1 J/g-°C. The carbon soles of a high-end road shoe weigh in the neighborhood of 100 grams each. But, treating the sole as a beam in bending, the vast majority of the strain (and therefore energy absorption) is happening over about 30% of that mass. Now we can apply the dissipated energy to the part of the sole that is actually flexing to calculate the temperature rise:

(120 Joules / 30 grams) * 1 J/g-°C = 4°C.

So the sole will heat up in the area right behind the cleat by 4°C (or 7.2°F). That's enough to feel.

Moreover, if temperature rises of 4°C were typical, one wouldn't need a thermal camera capable of distinguishing 0.02°C to study stress via imaging.

-------------------------

Now, I'm not discounting the importance of rider feel. Confidence is critical, and many people feel more confident knowing they've got a stiff frame or when they're wearing their special sprinting shoes. If you think you'll go faster, you often will—and that's the problem of trying to gauge these things by feel, even if a power meter is involved.

Once, when I was a junior, I was practicing sprints with my friend. He was usually a little better than me over 200m, so he was a great person to practice with. As I led out the first round, I clicked into my highest gear and gave it my all. I was expecting my friend to come around me and beat me to the line by half a bike length or so, but he didn't. When I crossed the line and looked back, I saw that I had ridden him right off my wheel. It was amazing!

Here's what happened: I believed I was riding with junior gearing, which at the time was limited to a 53/15 gear. But in fact I had put on the wheel I used for senior races, which gave me a 53/13 gear. My friend had the same gearing, but I was expecting to turn a 53/15 at about 125 RPM. I hit maybe 110 RPM in my 53/13 without realizing anything was amiss.

So yeah, confidence helps you make watts, no doubt. Stiffness, however, does not.


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PostPosted: Wed Nov 16, 2016 2:34 am 
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pdlpsher1 wrote:
youngs_modulus- who are you? Are you BRM? Are we just wasting our money on marketing BS?

Um, nope. I'm me.

If it helps, I'm the guy who did the strain energy analysis for the Fairwheel crank article.

Yeah; I'd say lots of people are wasting their money on marketing claims. I'd call it BS, most of it isn't, at least not in the sense of "an intentional lie told by marketers."

Keep in mind that most product managers are not engineers and may well have zero scientific training. As I said before, "power transfer" is meaningless in an engineering sense, but I'd bet most product managers who talk about their product's "improved power transfer" sincerely believe that their new, stiffer part delivers more power to the road.

I'd also argue that consumers are holding companies to their claims as never before. We cyclists are living in a golden age of data...many of us have power meters; Fairwheel publishes stiffness numbers for a bunch of components; Tour, Velonews and many others publish frame stiffness numbers and/or useful aero data, while others quantify tire rolling resistance. "Marketing BS" has never been more threatened. It's great!

IMHO, when a rider says a frame has "great power transfer" what they mean is "this bike feels a lot stiffer and more efficient than other bikes I've ridden." And that's a valid thing to say...the bike feels good to the rider, which is awesome. But scientifically, better "power transfer" is not sending power to the wheels that was previously lost to "flex," simply because almost no power at all is lost to elastic strain.


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PostPosted: Wed Nov 16, 2016 9:04 am 
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youngs_modulus wrote:
cyclespeed wrote:
It's important to have as direct and stiff a line of power transfer as possible, especially for a sprinter, where instant reaction is required.

I'm not trying to pile on, cyclespeed. But your comment points to something many people miss: you don't get more power or "faster response" from a stiffer shoe or even a stiffer frame..


Good to have someone that works in this field and has far more hands on experience than me. With a name like Young's Modulus, you have to assume this is your area. It's interesting stuff.

Not sure I said you'd get 'more power' though. And maybe 'faster response' is not the best way to express it, but surely the stiffer a component, the 'better' it transmits power.

Guess you just have to define 'better'.

Sprinters are well known for choosing extra beefy stems and thick alu handlebars so there must be a reason for this?

Many years ago I had an early Easton carbon handlebar (26.2mm?) on a light, flimsy stem. A beefy bike shop owner one day said to me, 'how can you ride that?' and then proceeded to demonstrate how he could flex the bar ends about 2cm or so from end to end. I changed to the new 31.6mm standard soon after that.......

I would still contend that if you want an instant reaction from your power input, the stiffer the better. Imagine you rode with thick rubber cranks. At low powers they'd work fine. But stomp on them and there'd be all kinds of springiness, feedback, damping effects, etc.etc. Surely better to have them as stiff as possible? Happy to learn why not, if that's the case......

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PostPosted: Wed Nov 16, 2016 3:10 pm 
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cyclespeed wrote:
youngs_modulus wrote:
cyclespeed wrote:
It's important to have as direct and stiff a line of power transfer as possible, especially for a sprinter, where instant reaction is required.

I'm not trying to pile on, cyclespeed. But your comment points to something many people miss: you don't get more power or "faster response" from a stiffer shoe or even a stiffer frame..


Good to have someone that works in this field and has far more hands on experience than me. With a name like Young's Modulus, you have to assume this is your area. It's interesting stuff.

Not sure I said you'd get 'more power' though. And maybe 'faster response' is not the best way to express it, but surely the stiffer a component, the 'better' it transmits power.

Guess you just have to define 'better'.

Sprinters are well known for choosing extra beefy stems and thick alu handlebars so there must be a reason for this?

Many years ago I had an early Easton carbon handlebar (26.2mm?) on a light, flimsy stem. A beefy bike shop owner one day said to me, 'how can you ride that?' and then proceeded to demonstrate how he could flex the bar ends about 2cm or so from end to end. I changed to the new 31.6mm standard soon after that.......

I would still contend that if you want an instant reaction from your power input, the stiffer the better. Imagine you rode with thick rubber cranks. At low powers they'd work fine. But stomp on them and there'd be all kinds of springiness, feedback, damping effects, etc.etc. Surely better to have them as stiff as possible? Happy to learn why not, if that's the case......


but bike shoe soles are not made of rubber. you're talking about the incremental stiffness between already-stiff soles. 300w, 75rpm, 175mm cranks, thats about 50 lbs applied to the pedals ... which i dont think is too much demand compared to whats available on the market


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PostPosted: Wed Nov 16, 2016 3:16 pm 
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my theory is that flexible systems (shoes, drivetrains) may inhibit power generation due to two factors. In shoes, a flexible shoe may allow excessive pronation, which could lead to force vectors not aligned 90 degrees to the pedal, which by definition would be wasted power i.e. energy spent that does not contribute to forward motion.

In drivetrains, we are measuring power with cranks that measure forces at discreet angles/in packets, and are not actually measuring continuously. At the same time, it's clear the force vectors are not equal throughout the pedal stroke. We get good at building efficiency through the pedal stroke by doing a huge number of repetitions, but there can be a large difference in force generation from one pedal position to 30 degrees later. When there is a high degree of flexibility in the drivetrain, those neurological efficiencies we've built may get reduced because the crank/pedal may not be exactly where our neuro system expects them to be.

related to the flexible shoe theory, I've certainly felt this to some degree on an old bike where the pedal cambered so much under high load I could feel it in my foot supinating, therefore some of the downward force was being sent sideways, which is completely non productive at that moment. Yes, it is elastic deformation, but it returns to natural state near the bottom of the pedal stroke, where vertical forces are again, non productive.

Theory aside, if the big sprinters want a stiff bike because it feels better, give them what they want!


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PostPosted: Wed Nov 16, 2016 3:48 pm 
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gewichtweenie wrote:
300w, 75rpm, 175mm cranks, thats about 50 lbs applied to the pedals


An important point!

I can generate about 1100W for 10s max, and during this I am pushing my soles with a lower force than when climbing stairs!


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Posted: Wed Nov 16, 2016 3:48 pm 


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