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Stiffness Does Not Matter

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Stiffness Does Not Matter

Old 08-23-21, 07:27 AM
  #26  
mstateglfr 
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Originally Posted by ShannonM View Post
There's a meme (in the original sense of the word, a unit of cultural heredity, not the modern stupid-picture-of-a-cat-with-a-stupid-saying-in-white-letters sense,) that has been replicating in the brains of humans who ride bicycles for many, many years... and it's nonsense.

That meme is this:

Flex in the bicycle dissipates some fraction of the force generated by the rider's muscles.

This is simply, physically, not true. The thing that it's describing does not actually happen. Numerous attempts have been made to measure this "power loss." So far as I'm aware, nobody has ever been able to repeatably detect any power loss due to bicycle flex that is above the noise floor of the equipment used to do the measuring.

And, because the meme isn't actually true, this statement is true:

Unless the bicycle and/or its components are so flexible as to have negative effects on handling, alignment, or durability, the stiffness of any part of the bicycle or the bicycle as a whole is utterly irrelevant to the performance of the bicycle.

Stop caring about the stiffness of your frame, cranks, wheels, stem, handlebar, pedals, brake levers, (yes, I've seen stiffness referred to in brake lever reviews,) or any other part of your bicycle with the possible exception of racks. (And even they're not much of an exception... any rack strong enough for the load you're putting on it will be stiff enough for that load... if it wasn't, it'd break.)

Stiffness does not matter.

--Shannon
While it may not mean much in terms of energy loss, that doesnt mean a flexible bike doesnt matter. I dont want a bike where I ghost shift when I stand and climb. I dont want a bike where the wheels are visibly twisting and rubbing the brake pads.
The phrase 'laterally stiff and vertically compliant' is rightfully made fun of, given how often it is used in marketing, but its legit.
I have never heard someone say 'man, I wish this bike twisted more when I pedal' because that isnt a thing.
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Old 08-23-21, 07:28 AM
  #27  
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In general, the benefit of "stiffness" in a bicycle increases with rider weight and decreases with road/trail roughness. A heavy rider on smooth pavement gets the most benefit from a stiff bicycle; a light rider on rough pavement, the least.
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Old 08-23-21, 08:32 AM
  #28  
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Old 08-23-21, 08:41 AM
  #29  
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Originally Posted by JohnDThompson View Post
In general, the benefit of "stiffness" in a bicycle increases with rider weight and decreases with road/trail roughness. A heavy rider on smooth pavement gets the most benefit from a stiff bicycle; a light rider on rough pavement, the least.
Experienced plenty of, um, noise / vibration / harshness when we were growing up, riding in the fields. More vibration when barreling down the bluffs to the jump we'd made at the bottom ... but more harshness when landing over the tracks and in the cactus patch on the other side. (Heavy or light didn't seem to matter, picking ourselves up from the cactus patch. But, boy! were we stiff ... )
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Old 08-23-21, 09:00 AM
  #30  
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Originally Posted by Phil_gretz View Post
Total market value, 2020, from Mordor Intelligence, an investment analysis firm. Projections are a bit droopy out to 2026, though.
OH I am sure , BUTT , a little play on the word used before the *---* that had I used instead of *believe* most likely would have gotten me in trouble.

r.e. -- droopy , might also need to consider a possible Peyronie's disease syndrome when extrapolating.
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Old 08-23-21, 09:08 AM
  #31  
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I know it's invited by the OP, but could we just avoid the obvious juvenile double entendres for once?
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Old 08-23-21, 09:16 AM
  #32  
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It’s pretty easy…

The more flexible you are, the less flexible your bike needs to be.

The less flexible you are, the more flexible your bike needs to be.

Some mornings I wish I had a Vitus.

John
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Old 08-23-21, 09:27 AM
  #33  
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Oh, and here I was thinking about what the little blue pill is for - ALEVE for stiffness after a ride!
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Old 08-23-21, 10:24 AM
  #34  
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Originally Posted by freeranger View Post
Guess all the fork manufacturers that built a lock-out in their design have wasted their money? I would think the motion of a suspension fork could qualify as "flex".
Not even close to the same thing. A suspension system (front or rear) on a bicycle is intended to take the energy of an impact and use it to generate heat elsewhere. An undesired side effect is that the force of pedaling also acts on the suspension, so some of the force gets turned into heat.

The OP is speaking of force which is played into an undamped spring and which is overwhelmingly played back.
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Old 08-23-21, 10:35 AM
  #35  
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I look forward to OP's new bike made of pad thai
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Old 08-23-21, 10:45 AM
  #36  
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Originally Posted by Darth Lefty View Post
I look forward to OP's new bike made of pad thai
You don't think it'll be all noodly?
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Old 08-23-21, 10:47 AM
  #37  
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I call BS. Frame flex matters a great deal for my recumbents. My stiffest bent is also the best climber of the bunch, likewise my flexiest one is the worst climber. (Climbing relies less on aerodynamics and more on power input.) Even if we're talking about traditional 'double diamond' frames, there is a difference. Power lost deforming the frame is never recovered for propulsion.
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Old 08-23-21, 10:51 AM
  #38  
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Originally Posted by freeranger View Post
Guess all the fork manufacturers that built a lock-out in their design have wasted their money?
Not their money, no, but they’ll keep us wasting ours as long as people on the Internet tell other people on the Internet that suspension forks are “inefficient”
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Old 08-23-21, 11:16 AM
  #39  
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Originally Posted by ShannonM View Post
Stiffness does not matter.
That's not what she said.
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Old 08-23-21, 11:36 AM
  #40  
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So really, this is just another “my saddle makes my junk go numb” thread.

There are a few suggestions to add to the quality here.

-Sildenafil has shown promise among high altitude mountaineers and theoretically could be helpful as a performance enhancing drug for endurance athletes.

-Has anyone ever experienced the unexpected diamond cutter when waking the nethers back up? My current seats don’t cause this but I have experienced it in the past.

Carry on
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Old 08-23-21, 11:41 AM
  #41  
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Seriously, I'm no physics expert, but it's only logical that if the exertion you're putting into moving your bike across the ground is also causing some flex in the frame, then part of your effort is wasted in bending the frame back & forth. Or, the frame is absorbing some of the force instead of putting it fully into the pedals. I'm sure someone might show some science to prove me wrong, so have at it...
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Old 08-23-21, 12:59 PM
  #42  
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Originally Posted by Milton Keynes View Post
Seriously, I'm no physics expert, but it's only logical that if the exertion you're putting into moving your bike across the ground is also causing some flex in the frame, then part of your effort is wasted in bending the frame back & forth. Or, the frame is absorbing some of the force instead of putting it fully into the pedals. I'm sure someone might show some science to prove me wrong, so have at it...
Can't say I've ever see watts measured at the pedals and also at the pavement at the same time to disprove anything. Or to prove anything.
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Old 08-23-21, 01:25 PM
  #43  
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Originally Posted by Milton Keynes View Post
Seriously, I'm no physics expert, but it's only logical that if the exertion you're putting into moving your bike across the ground is also causing some flex in the frame, then part of your effort is wasted in bending the frame back & forth. Or, the frame is absorbing some of the force instead of putting it fully into the pedals. I'm sure someone might show some science to prove me wrong, so have at it...
Where does the energy go? Does the frame flex and stay in that position? No, it flexes back. Does the frame get hot? No. Pretty much all the energy that causes the frame to flex is returned.
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Old 08-23-21, 01:27 PM
  #44  
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Originally Posted by Metieval View Post
Can't say I've ever see watts measured at the pedals and also at the pavement at the same time to disprove anything. Or to prove anything.
i suppose it would be possible with two frames, indoors, same weather, same rider, same wheels and tires and cassette, same chain, brand new matching cranks, add some weights to match up frame weights, same power pedals, ride at a predetermined cadence and power and carefully measure speed of the bicycle.

it would be pretty surprising if the difference between a noodly frame and a worlds-stiffest would be measurable, or above the margin of error of the experiment. but it would probably feel totally different to the rider, which is what’s actually important for most of us.
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Old 08-23-21, 01:40 PM
  #45  
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Here’s a good video covering stiffness and Young’s Modulus, he shows some good modeling and decent figures also mentions some studies.


Further reading about bike engineering, and materials analysis in some studies about frame types, geometries, and materials specifically referencing FEA (which is method for numerically solving differential equations arising in engineering and mathematical modeling)

Enjoy.


Derek Covilla, 2014. “Parametric finite element analysis of bicycle frame geometries”, the conference of the International Sports Engineering Association 2014, Elsevier Procedia Engineering 72 (2014) 441 – 446

Bharati A. Tayade, 2015. “A study on structural health of bicycle frame using Finite Element Analysis”, International Journal of Innovative and Emerging Research in Engineering Volume 2, Issue 4

Joachim Vanwalleghema, 2014. “Development of a multi- directional rating test method for bicycle stiffness”, the conference of the International Sports Engineering Association, 2014, Elsevier Procedia Engineering 72 (2014) 321 – 326

M.A. Maleque, 2010. “Materials Selection Of A Bicycle Frame Using Cost Per Unit Property And Digital Logic Methods”, International Journal Of Mechanical And Materials Engineering (Ijmme), Vol.5, No. 1, 95-100

M.V.Pazare, 2014. “Stress analysis of bicycle frame”, International Journal of Engineering Science and Technology (IJEST), ISSN: 0975=5462, vol. 6, No. 6

Aparna Deshpande, 2016. “Design and Optimization of Bicycle Frame for the Cyclist's Comfort”, International Journal on Recent and Innovation Trends in Computing and Communication, ISSN: 2321-8169, Volume: 4 Issue: 5 220 – 224
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Old 08-23-21, 02:36 PM
  #46  
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Originally Posted by unterhausen View Post
I know it's invited by the OP, but could we just avoid the obvious juvenile double entendres for once?
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Old 08-23-21, 02:41 PM
  #47  
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Well, a bicycle that wiggles on turn-in has a weak frame but the poster allowed for that.

Now, aluminum that flexs then cracks. So aluminum is used in larger cross-sections than steel. Allowing for the larger cross-sections then the weight advantage of aluminum over steel is only about 5%. However, current aluminum frames have smaller cross-sections than the original aluminum frames. Now the forks can be carbon-fiber and that helps.

Presently, carbon-fiber frames often have seat or handlebar compliance systems.

Last edited by KKBHH; 08-23-21 at 02:44 PM.
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Old 08-23-21, 04:42 PM
  #48  
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I thought the current theory is that a flexy frame doesn't keep the rear wheel inline with the frame during hammer time, and that is a source of energy waste.

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Old 08-23-21, 04:45 PM
  #49  
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Originally Posted by Koyote View Post
This thread title is like a nice easy pitch right down the middle… But I don’t want to get banned.
I had the exact same thought ...
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Old 08-23-21, 04:54 PM
  #50  
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Originally Posted by cxwrench View Post
Where does the energy go? Does the frame flex and stay in that position? No, it flexes back. Does the frame get hot? No. Pretty much all the energy that causes the frame to flex is returned.
Even if all the energy that goes into flexing the frame is returned, it may not be returned in a way that propels the bike forward. You have to look at the whole system and where the losses are.
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