High stiffness and performance gain

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WMW
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by WMW

LetsRide wrote:Cycling Weekly just tested "How does weight affect your climbing speed? (video)"
http://www.cyclingweekly.co.uk/news/lat ... deo-186771


Physics works really well to show the effects of weight on a climb. Their test results just prove they had a sloppy protocol.
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WMW
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by WMW

Franklin wrote:Wait... what's so magical of the flex being directed towards the rider? And what's magical about the body acting as a dampener?


Because it doesn't happen. You are thinking about it wrong, that's all.

The rider isn't damping anything, the rider is applying force. The frame doesn't spring back during the dead part of the stroke, it springs back in the later half of the power stroke. Like I've said a dozen times it modifies the force and motion curve slightly.

And I don't feel like spending time trying to explain it to people who don't understand physics but are still sure they are right. Sorry.
formerly rruff...

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Franklin
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by Franklin

WMW wrote:
Franklin wrote:Wait... what's so magical of the flex being directed towards the rider? And what's magical about the body acting as a dampener?


Because it doesn't happen. You are thinking about it wrong, that's all.

The rider isn't damping anything, the rider is applying force. The frame doesn't spring back during the dead part of the stroke, it springs back in the later half of the power stroke. Like I've said a dozen times it modifies the force and motion curve slightly.

And I don't feel like spending time trying to explain it to people who don't understand physics but are still sure they are right. Sorry.

Okay, I'm rolling my eyes here. A riders body most certainly dampens road effects. You do a huge arrogant handwave saying that does not apply with pedaling power and that people here do not understand physics, only you do... so no need to come with proof.

Sorry I had respect for your work, but you are very rapidly disqualifying yourself with this attitude.

TheKaiser
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by TheKaiser

WMW wrote:
TheKaiser wrote:I overstated, based on the evidence I cited, when I said "peaking", thank you for the correction. What I was taking into account was that, even though max force is at 100 degrees, as the crank arm swings down toward 6 o'clock the length of the lever flexing the BB sideways increases so, even though force is lower, leverage is greater.


The lateral distance between the force vector (the pedal) and the centerline of the bike is constant. That's the one causing the BB to flex sideways.


That would be true if the bike and rider were locked on a linear plane, but, particularly under vigorous pedaling, and certainly under standing efforts, the bike will sway side to side and the force vector is no longer delivered in the same way. An extreme example, for the purposes of illustration, would be if you were to lay the bike over at a 45 degree angle and apply weight to the pedal. Try it with the pedal at 12, 3, and 6 o'clock and then come back and tell me that the force vector that causes sideways flex is constant regardless of pedal position.

Not that I think anyone will actually do this test, but, if you were to do so, you may need to pull the left crank arm to avoid adding an additional point of support to the structure, if your left pedal hits the ground.

My point is simply to illustrate the the total collection of lateral flex components is a complex one, and difficult to model, and so I think it is wishful thinking to simply assume that when the frame springs back it will magically result in forward motion, without any losses. On the other hand, I suppose you could argue that the lateral flex that I referenced above, with the bike leaned at 45 degrees, would actually result in the bottom bracket twisting into a more normal position relative to the force component being delivered by the riders foot. That could therefore, result in a more effective delivery of force to the drivetrain. By that, I mean that the rider is pushing more or less straight down, but the bike is leaned to the side meaning that force is being delivered tangentially to the crank's plane of rotation. As the BB deflects and twists downward, it will bring the tangent back into line with the riders force delivery to some degree.

LetsRide
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by LetsRide

Just found this article listed below from Cervelo Facebook page. "Power transfer is one aspect of BB stiffness, but the loss is at most 0.3% to 4% depending on if you’re cruising along or a world class sprinter."
See more at: http://www.cervelo.com/en/engineering/ask-the-engineers/industry-standards-part2.html

Let's say.
100 watts of easy riding -> 0.3% = approx 0.3 watt loss
1000 watts of sprinting -> 4% = approx 40 watts loss

This seems interesting. No idea how Cervelo find % power loss from BB stiffness (N/mm), from software modeling or from test riding ?

data from Giant's tests
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Rick
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by Rick

If we consider that neither the cranks nor the frame end up in a permanently distorted (bent) state, and apply Betti's Theorem, then I think that proves that no mechanical energy has been "wasted", regardless of how complex the load and relaxation distortions may have been.
https://en.wikipedia.org/wiki/Betti%27s_theorem

(I am kidding a little here, but the principle really does apply. No permanent deformation or detectable temperature increase = no energy "lost")

The biochemical energy demand on the rider might be a different story, because, for example, you could press all day LATERALLY on a crank arm, and do absolutely no detectable mechanical work, but still have very fatigued muscles and be genuinely tired and have expended energy as nutritional calories. But that is the realm of physiology, etc, not mechanical work/energy.

So a flexy frame really might make you more "tired"....but it could just as easily be the opposite: maybe a stiff frame makes you more "tired" by beating you up on bumps.
Just a data point: Sean Kelly once remarked that his favorite bike was one of those aluminum Vitus frames, notorious for their flexiness. Yet somehow he had not "lost" enough energy to sprint for wins in major classics.

LetsRide
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by LetsRide

Rick wrote:So a flexy frame really might make you more "tired"....but it could just as easily be the opposite: maybe a stiff frame makes you more "tired" by beating you up on bumps.
Just a data point: Sean Kelly once remarked that his favorite bike was one of those aluminum Vitus frames, notorious for their flexiness. Yet somehow he had not "lost" enough energy to sprint for wins in major classics.


As technologies advance in composite material and layup technique, modern carbon frames can be made both stiff and flexy at the same time but in different area. So stiff frame yet still comfortable can be possible. This thing might sound ridiculous in the past.

For example, BMC's Tuned Compliance Concept, blue area is designed to be stiff meanwhile brown area is designed to be flexy.
http://www.bmc-switzerland.com/int-en/innovation/#c1432
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chainstays of 2014 Trek Madone
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DeLuz
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by DeLuz

tinozee wrote:I have an s-works SL3 tarmac and it is so stiff. I now race on evo hi-mod and it is so comfortable! I will have to test some short sprints on the trainer, maybe 10 zwift green jersey sprints on each bike in same form (using training peaks or strava). I think I could do a ballpark comparison of sprint efficience with that setup. But over 100 mile best effort the Evo destroys the tarmac for me.


I had the same exact thing. The Tarmac SL3 was so stiff it beat me up on bad or even not so bad roads.
Sold it and bought a Cannondale EVO (non HiMod) and it is so much smoother.
I probably ride faster because less fatigue.
All top race race bikes are stiff enough to not effect performance by anything worth worrying about.
Pro cyclists win races on all sorts of brands.

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by BeeSeeBee

LetsRide wrote:As technologies advance in composite material and layup technique, modern carbon frames can be made both stiff and flexy at the same time but in different area. So stiff frame yet still comfortable can be possible. This thing might sound ridiculous in the past.


Truthfully, It sounds ridiculous even today. It's that "laterally stiff, vertically compliant" line we used to roll our eyes at, but at some point adopted as truth without actually being shown any proof. I haven't been able to get a straight answer from any manufacturer about actual measured vibrational response or deflection numbers across various terrains, not just numbers quoted at the extremes (e.g. 1000N of force deflecting 10mm vs 5mm). If I hit a bump to produce that degree of force, am I going to notice 5mm of deflection as I'm bucked out of the saddle?

What's going to feel better, getting hit with an aluminum or a carbon baseball bat?

A lot of the stuff in the new Madone white paper was seriously talking about differences on the order of 0-2mm (not the comfort aspect, which again they didn't qualify at what force, but deflection while cornering and other stuff). Of course the plots exaggerate the differences, but a marketing spin is expected on them.

But this is also great, because like DeLuz, they're all seriously capable bikes these days that we're splitting hairs and wringing our hands over. Not that it isn't fun to do that, but perhaps we're putting too much emphasis on stuff that realistically won't materialize in any perceptible way.

LetsRide
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by LetsRide

Fortunately, we don't need to read whitepapers to understand how stiff and comfortable could be. Go test riding is the easy way. There are several bikes with such claims. Just in case you don't have one in mind, I would suggest to try SuperSix Evo Hi-mod, especially the new 2016 model.

highdraw

by highdraw

BeeSeeBee wrote:
LetsRide wrote:As technologies advance in composite material and layup technique, modern carbon frames can be made both stiff and flexy at the same time but in different area. So stiff frame yet still comfortable can be possible. This thing might sound ridiculous in the past.


Truthfully, It sounds ridiculous even today. It's that "laterally stiff, vertically compliant" line we used to roll our eyes at, but at some point adopted as truth without actually being shown any proof. I haven't been able to get a straight answer from any manufacturer about actual measured vibrational response or deflection numbers across various terrains, not just numbers quoted at the extremes (e.g. 1000N of force deflecting 10mm vs 5mm). If I hit a bump to produce that degree of force, am I going to notice 5mm of deflection as I'm bucked out of the saddle?

What's going to feel better, getting hit with an aluminum or a carbon baseball bat?

A lot of the stuff in the new Madone white paper was seriously talking about differences on the order of 0-2mm (not the comfort aspect, which again they didn't qualify at what force, but deflection while cornering and other stuff). Of course the plots exaggerate the differences, but a marketing spin is expected on them.

But this is also great, because like DeLuz, they're all seriously capable bikes these days that we're splitting hairs and wringing our hands over. Not that it isn't fun to do that, but perhaps we're putting too much emphasis on stuff that realistically won't materialize in any perceptible way.


I just don't agree in bold. Changes to new frames aren't unsubstantial or incremental, there is a huge trend in the bike industry toward frames that are super stiff laterally with more forgiveness in the vertical plane. Take Specialized. The replacement for the Tarmac SL3 which was complained about in the pro peloton as being overly vertically stiff was changed with the SL4...made friendlier to ride in the vertical plane and more laterally stiff at the same time. Virtually nobody will disagree that the SL4 is a much better bike and has turned out to be one of the best race bikes every conceived. Some say that Specialized in fact $h!t the bed with the new Roubaix SL4 which was taken in the opposite direction. Specialized changed the rear triangle of the bike and made it more like the Tarmac in back...much stiffer...resulting in supposition that the change in lateral stiffness actually degraded ride quality as the planes though opposite are in fact related...because a frame technically bends rotationally or torsionally as viewing a bike from the front. As a result, testers of the new Roubaix SL4 found the bike overly stiff to ride...not in the character of an endurance genre bike...the SL3 Roubaix being more the sweet spot of ride comfort and overall stiffness which was much improved from the Roubaix SL2 which by comparison was considered a noodle and not a performance oriented bike.

The new Cervelo SL3 comes to mind...a bike with unprecedented vertical compliance for an aero bike while not a noodle laterally. Cervelo did this by making the seat seats uber compliant and the bulk of the stiffness of the rear of the bike based upon super stiff chainstays. In fact many believe the S3 rivals the ride quality of the R3 and why many choose the S3 as there is little downside to the aero frame qualities. This is a very difficult balance to achieve with an aero bike and the S3 is actually a more livable bike within the aero genre as a result than the less aero Venge or more aero S5 which is often criticized for riding like a cattle wagon.

So what designers are trying to accomplish is not without consequence...it is in fact the cornerstone of how bikes perform and how livable they are to ride. I believe the thing that is striking is the notion of why laterally stiffness matters. We all understand why vertical deflection matters...to absorb road shock which is principally vertical in plane and attenuate rider assault and fatigue. But in spite of when this conversation comes up...and its a compelling one I often enjoy and generally without resolution, there is one immutable reality. Bike companies want to make make their top race bikes as laterally stiff as they can. This is the common theme in the industry and the consensus of thousands of engineers that make up the industry. So why is that? Is a laterally stiffer bike faster? Does it accelerate faster? Does it tire a rider less when hammering for 50 miles in a competitive environment?...provided a given race bike has suitable vertical compliance? I believe this all maybe true and of course we all struggle to produce the math or even power meter numbers to support this. But the industry is in lockstep and I believe anybody who believes this is pure marketing is wrong. Its a substantive position. Will a better rider on a flexy bike beat a weaker rider on an uber laterally stiff bike? Like a red headed step child all day long. There are guys I can't outsprint who ride Columbus tubing steel bikes when I am on my carbon rocket ship. So the stiffness thing is not transformational as most here know who compete on the recreational level. But a stiffer bike 'may' climb and sprint better for a stronger rider in particular.

I also think some of the terminology used here is a bit sketchy. When a flexy frame it loaded or a top sprinter loads even a stiff frame that an average rider can't even flex, the frame 'stores' that energy. It isn't absorbed. There is very little heat loss if any. When a strong rider is out of the saddle, and the rider pushes his legs against the resistance of the road, the frame bends and more or less holds this bend as the rider imparts more energy than what the road pushes back aka the bike accelerates. But does the frame really hold this bend? Truth is, the frame doesn't. This is because a rider's application of power to the bike isn't linear. Its cyclic....like a pulse. The pedal stroke has a power zone and a flat zone and there are two pedals on a bike. So one would think intuitively once the frame stores energy than acceleration of the bike should be same between a stiff bike and a more flexible bike for a given rider wattage. But, I believe the benefit of frame lateral stiffness or resistance to frame torqueing may be more nuanced than that including where the real improvement in power transfer is. I believe it relates to the cyclic power of crank rotation. The power zone of the pedal stroke versus the dead zone. The reciprocating power left to right. This is sine wave of power application as it turns out. It is possible that the loss of efficiency of a flexy frame relates to the transition of dead zone to power zone of pedal rotation. Call this the power pulse. This pulse is more affected by a flexy frame which may slightly unwind every time power to the pedals is reduced. So I believe if one views power to the pedals as more of a pulse of on and off power...like a crankshaft firing close to TDC and there physically being a lag in power after the leg(s) fire thru the power zone, this probably interacts more with a flexible frame aka a stiffer frame transfers the power of the pulse more efficiently to powering the bike forward because there is less unwinding of a stiffer frame through the dead zone of pedal power on each side...so a stiff frame picks up the power zone of pedal pedal force more quickly...and this all occurs several times a minute in the 90-140 crank RPM range.

A good conversation in any event and one of almost indiscernible solution because of magnitude mostly....a good rider will beat an average rider every time on a more flexible frame.

But again, the industry marches forward with greater laterally stiff bikes and I believe its because they are tangibly faster among better riders based upon above. So I agree with the industry trend as vertical and lateral stiffness are further decoupled to have one's cake and eat it too.

Also, if you take a 1500 watt sprinter versus 500 watt Joe six pack weekend warrior, the stiffness of the frame becomes moot to Joe six pack. Joe six pack has a hard time flexing a Vitus frame often discussed as a benchmark or contrast to a stiff frame. A Vitus is almost a stiff bike to Joe six pack versus a decent amateur sprinter. So frame stiffness matters relative to who is riding the bike and whether a given frame stiffness will matter more or less. If a rider can't flex a modestly flexible frame, then there isn't any efficiency loss.

A final note. Higher lateral frame stiffness may at the end of the day matter for control of the bike during a sprint. A stiffer bike in the hands of a strong guy maybe easier to control out of the saddle when laying down big watts compared to a more flexible bike and this will translate into greater speed. So this maybe part of the calculus as well.
Last edited by highdraw on Sat Sep 12, 2015 3:52 pm, edited 1 time in total.

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kgt
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by kgt

LetsRide wrote:Fortunately, we don't need to read whitepapers to understand how stiff and comfortable could be.

+1
Comparing my 2015 Cipollini Bond to my 2009 Wilier Cento there is no doubt the Bond is much stiffer.
Comparing my 2009 Wilier Cento Uno to my 2015 Cipollini Bond there is no doubt Cento Uno was more comfortable.

That does not mean I am actually faster or spend less energy on either a or b. It's all about how a frame feels and what kind of feedback one prefers.
I love the ride of my 1996 steel Pinarello Dyna although it is a noodle in comparison tomodern carbon frame. And I am pretty sure Indurain would still be competitive riding it.

dmulligan
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by dmulligan

Until recently my only ride was a 2009 Kona Jake. A vertically stiff and laterally flexible aluminium bike upgraded with stiff aluminium wheels and super high pressure 23mm tyres. I then got a 2014 Cervelo R3, a vertically compliant and laterally stiff bike. At first I equipped it with the same wheels and tyres. The difference in lateral stiffness was day and night where the vertical compliance was noticeably better but not what I had hoped. However the first pedal push from a stop feels more connected in the way that the bike starts moving sooner, it lurches forward. I don't know how to explain it bit the bike just feels like it wants to go. Then I changed to lower pressure GP4000SII tyres, 25mm in the back and 23mm in the front. That made a much bigger difference in vertical compliance without taking lateral stiffness away.
Am I faster for it? I feel like I am faster and I am happier to lay down all of the power I've got.

I suck at hill climbing. Looking down at my Jake's frame bending was demotivating while suffering an up 8% grade. I still suffer on the same hill on my R3 but I consistently climb it just a little faster. (Not that I've tried THAT hill with my Jake since.)

Sent from my Oneplus One using Tapatalk

highdraw

by highdraw

dmulligan wrote:Until recently my only ride was a 2009 Kona Jake. A vertically stiff and laterally flexible aluminium bike upgraded with stiff aluminium wheels and super high pressure 23mm tyres. I then got a 2014 Cervelo R3, a vertically compliant and laterally stiff bike. At first I equipped it with the same wheels and tyres. The difference in lateral stiffness was day and night where the vertical compliance was noticeably better but not what I had hoped. However the first pedal push from a stop feels more connected in the way that the bike starts moving sooner, it lurches forward. I don't know how to explain it bit the bike just feels like it wants to go. Then I changed to lower pressure GP4000SII tyres, 25mm in the back and 23mm in the front. That made a much bigger difference in vertical compliance without taking lateral stiffness away.
Am I faster for it? I feel like I am faster and I am happier to lay down all of the power I've got.

I suck at hill climbing. Looking down at my Jake's frame bending was demotivating while suffering an up 8% grade. I still suffer on the same hill on my R3 but I consistently climb it just a little faster. (Not that I've tried THAT hill with my Jake since.)

Sent from my Oneplus One using Tapatalk

In bold is key and often recited about the latest uber laterally stiff race bikes. In and of itself, this isn't a big revelation however I wrote above about why it matters. It just isn't the first pedal stroke. It is the bikes response to each pedal stroke because each pedal stroke...about 90-130 of them per minute....is comprised of both a power zone and a dead zone. So another way of looking at it is...the bike is constantly experiencing starts and stops with each pedal stroke. A stiffer bike will pick up each power stroke earlier with less elastic deformation, just like the initial take off power stroke propelling the bike forward. Having thought about why a stiff bike is faster than a flexible bike, I believe is best considered if you think of the pedal stroke as a pulse of finite duration. What is a power stroke? It is really the acceleration of the crank and applying a force greater than the energy sustaining the forward momentum of the bike. This pulse or input is responded to sooner compared to a more flexible bike which has more lag for each power stroke because during the dead zone when the frame has more stored energy than the lack of power applied, the frame unwinds and returns some of the stored energy. This is the best explanation I can come up with as to why a stiffer bike is faster than a flexible one. It isn't just the first pedal stroke or power stroke which loads the frame and energy is stored and not applied toward propelling the bike. If that were the case, a flexible bike after the first power stroke would be as fast as a stiff bike and I think this is what befuddles many. But rather is the sequence of power strokes which cumulatively powers the bike...a series of mini starts with each turn of the crank and how much deformation/restoration there is in response to each power and dead zone in aggregation is where the advantage occurs.

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LetsRide
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by LetsRide

Good to see this topic of discussion brought up :D

CyclingTips Podcast, Episode 32: Does frame stiffness matter?
by James Huang
June 6, 2017
https://cyclingtips.com/2017/06/cycling ... ss-matter/

What is Planing?
by Jan Heine, Editor, Bicycle Quarterly
https://janheine.wordpress.com/2014/11/ ... s-planing/

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