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Thread: What say Ye?

  1. #1
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    What say Ye?

    whatchathink?

    Too old to ride plastic

  2. #2
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    Is there a clif notes version?

  3. #3
    'brifter' is a lame word.
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    I completely believe them. Energy has to go somewhere, it can't be lost just because of some frame flex.
    I work for some bike racers
    I've got some bikes, some guns,
    and a bunch of skateboards

  4. #4
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    Don't think anyone has argued the energy simply disappears. The issue is whether the loss of energy from the frame flexing is returned in a beneficial way.

    Why does the energy have to go to the drive train?

    As the frame un-flexes, couldn't the energy go to lifting the opposite leg up (or changing the angle of both feet)?

  5. #5
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    Quote Originally Posted by crit_boy View Post
    Don't think anyone has argued the energy simply disappears. The issue is whether the loss of energy from the frame flexing is returned in a beneficial way.

    Why does the energy have to go to the drive train?

    As the frame un-flexes, couldn't the energy go to lifting the opposite leg up (or changing the angle of both feet)?
    This would also be beneficial, and, in a matter of speaking, be going to the drive train.
    Too old to ride plastic

  6. #6
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    The energy isn't lost, but it goes to a lot of places - and as they said in the video, it's really impossible to measure any of it, so it's all just speculation.

    Of course someone will come along here acting like they know everything and are smarter than the rest of us and tell us all exactly how it works...

    I can't wait...

  7. #7
    'brifter' is a lame word.
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    I'm guessing 4 pages before it's over.
    I work for some bike racers
    I've got some bikes, some guns,
    and a bunch of skateboards

  8. #8
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    I believe the "stiffer is faster" myth was debunked awhile ago.

    A stiffer frame, or specifically one that is stiffer in the BB area often makes the rider feel more connected, and therefore feel faster.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  9. #9
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    I subscribe to the Goldilocks theory.

  10. #10
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    I applaud their efforts, but their methodology has several shortcomings that make their results inconclusive.

  11. #11
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    Quote Originally Posted by tomato coupe View Post
    I applaud their efforts, but their methodology has several shortcomings that make their results inconclusive.
    Obviously, the chain stretched with the brake applied. Then contracted when the brakes was released.


    Ha... chain stretch adds 3 more pages.

    I'll go a head and ante up the Heine planing theory for 4 more pages.

  12. #12
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    So that's why my plastic cable guide on my bottom bracket melted..................(and set my socks on fire)
    If your opinion differs from mine, ..........Too bad.
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  13. #13
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    Quote Originally Posted by Lombard View Post
    I believe the "stiffer is faster" myth was debunked awhile ago.

    A stiffer frame, or specifically one that is stiffer in the BB area often makes the rider feel more connected, and therefore feel faster.
    IIRC it was 'debunked' by loud insistence that stiffness doesn't matter. Still an open issue IMHO. Even if the energy that goes into flexing the frame all comes back again, that doesn't convince me it's just as efficient for the human rider.

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    I'd rather be flexing a carbon, Ti or steel spring than a rubber sidewall.

    BB flex twists the chainstays, so the untwisting just compliments the other half of the pedal stroke. All the arguments about energy loss seem to involve it disappears into things that are already part of the drivetrain - like the legs.

    I imagine if you were to graph it the energy transmission just looks like Biopace - smaller peaks, longer taper.


    Riding a Vitus made me feel like flexible aluminum tubes do turn some flex to heat, which may explain why aluminum work hardens below its plastic deformation limit.
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  15. #15
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    An extreme example of how energy can be lost due to frame stiffness?

    Too old to ride plastic

  16. #16
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    Neutralizing the force to just one pedal without showing the bigger picture of how the frame flexes to accommodate the unrealistic scenario presented here, renders this entire video moot. I would wager anything that the flex perpetuated all throughout the horizontal axis of the frame.

    One thing you have to measure is the force exerted at the point of emphasis and then measure the resonance as it travels out from that point. You will see a linear relationship along a single axis and then an exponential drop along each of the other axes. This is due to the transfer of energy from potential to kinetic and depends on the axis the force is being exerted upon.

    It's also important to note there are so many points of shifting directional energy on the crank it's almost impossible to measure the true significance of the energy loss/gain along the frame proportional to the direction of force being applied. My defacto guess is you're at a Net 0 due to the nature of the force being exerted along 360 degrees.

    I think there are a lot more variables in a 3D system than can be accounted for in this simple demonstration, but it does make you wonder how frame geometries and structural joints help contribute to the overall performance of a bike. Maybe the real question here should be more along the lines of arguing geometries and configurations versus frame flex. Or are they one in the same? Who knows.

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    I wish I was THAT good of a rider that it would make a significant difference for me

    I love these questions and the responses. Great read and I learn a lot form them. Bike design and how carbon is layered up to meet a specific response is intriguing.

  18. #18
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    Quote Originally Posted by crit_boy View Post
    Don't think anyone has argued the energy simply disappears. The issue is whether the loss of energy from the frame flexing is returned in a beneficial way.

    Why does the energy have to go to the drive train?
    This ^
    It really depends on the crank angle when the frame un-flexes.

    For instance, if you put the crank arms at 6 and 12 o'clock, and do the same test, the back wheel will not move when you release the rear brake (refer to video above).

  19. #19
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    To throw my uneducated hat into the ring:

    My understanding of where/how stiffness can be a benefit is the immediacy of the intent -> result. e.g. in a sprint when you push on the pedals ago *now* you want the bike to respond *now*. If various components flex they'll store that energy and it will eventually be released as the system un-flexes so the energy is never truly lost but the confidence of the rider and the strategic moment may be lost.

  20. #20
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    Quote Originally Posted by Z'mer View Post
    This ^
    It really depends on the crank angle when the frame un-flexes.

    For instance, if you put the crank arms at 6 and 12 o'clock, and do the same test, the back wheel will not move when you release the rear brake (refer to video above).
    And that wouldn't be a test that demonstrates anything about pedaling. But if you did the test you describe and the 6 o'clock pedal is loaded in the direction of crank rotation, instead of vertically, you WILL get the same frame flex and resulting load on the chain.

    The BB doesn't drop on the right because of verical load, it drops because the right crank arm is below wear the chainring is pulling on the chain. Then the left drops because the load on that side is below where the chainring is pulling on the chain.
    Last edited by Kontact; 02-06-2018 at 11:03 AM.
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  21. #21
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    Quote Originally Posted by Kontact View Post
    The BB doesn't drop on the right because of verical load, it drops because the right crank arm is below wear the chainring is pulling on the chain. Then the left drops because the load on that side is below where the chainring is pulling on the chain.
    I don't buy that. I think you would see the same frame flex if you replaced the chain drive with a shaft drive emanating from the center of the crank spindle.

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    Quote Originally Posted by tomato coupe View Post
    I don't buy that. I think you would see the same frame flex if you replaced the chain drive with a shaft drive emanating from the center of the crank spindle.
    Exactly. Power to the rear wheel is all about generating crank torque, which is pedal force times crank arm length. For purely vertical pedal force, the maximum torque is when the crank arm is horizontal, and zero torque when the crank arm is vertical.

    But if you stand up to pedal, you will still generate considerable down force on the pedals at 6 o'clock, and maybe continue to load the frame. If so, some portion of the frame un-flexing will be lost, as the un-flex at 6 o'clock has no torque component.

  23. #23
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    FWIW, I didn't watch the video and only skimmed the responses so...

    I didn't see where anybody mentioned the "escape" of energy as heat. Or more accurately, the conversion of kinetic energy into heat energy (which I think is technically still kinetic energy - it just doesn't propel a rider forward).

    Bend a paperclip back and forth a bunch of times. It gets hot. That is a loss of energy to the surroundings as heat. A flexing frame will also generate heat which is energy that was put into the system (bike) but no longer working to propel the bike/rider forward.

    Does that amount to a hill of beans in the real world? Not for me and I doubt any other recreational, non-pro, rider.

    That of course ignores the effects fatigue caused by vibration of a stiff frame. I think that would matter more.

  24. #24
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    Quote Originally Posted by tomato coupe View Post
    I don't buy that. I think you would see the same frame flex if you replaced the chain drive with a shaft drive emanating from the center of the crank spindle.
    The frame doesn't know were the crank arm is. And shaft drive motorcycles actually do act very differently under load than chain drive.


    But we don't have to argue about this. Get a buddy, a flexible framed bike and yank the pedal straight back from 6 o'clock. Tell us what it does.

    The BB isn't being flexed down - the chainstays are twisting because there is no other way for the compression on the chainstay to go anywhere else.
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    Quote Originally Posted by Kontact View Post
    The frame doesn't know were the crank arm is. And shaft drive motorcycles actually do act very differently under load than chain drive.
    Motorcycles are a whole different creature. Their engines produce the same torque through the full 360 degree rotation. Human engines do not -- they produce essentially no torque when the pedals are at 6:00 and 12:00.

    But we don't have to argue about this. Get a buddy, a flexible framed bike and yank the pedal straight back from 6 o'clock. Tell us what it does.
    Irrelevant. The forces applied to pedals by a real cyclist are overwhelmingly in the vertical direction.

    The BB isn't being flexed down - the chainstays are twisting because there is no other way for the compression on the chainstay to go anywhere else.
    A downward force on a pedal, regardless of the crank orientation, will cause the bottom bracket to tilt slightly downwards on the side of the pedal. The predominant motion, however, will be for the bottom bracket to move sideways, away from the pedal.

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