tensions in a bike frame

Discussion in 'Cycling Equipment' started by Amerigo, May 15, 2003.

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  1. Amerigo

    Amerigo Guest

    Hi, did any of you try to calculate the tensions in a bike frame, for example using a finite element
    software? any web site?

    thanks for any info
     
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  2. Phil Brown

    Phil Brown Guest

    >Hi, did any of you try to calculate the tensions in a bike frame, for example using a finite
    >element software? any web site?

    Not much tension in a bike frame. Most loads are compressive. Phil Brown
     
  3. Jobst Brandt

    Jobst Brandt Guest

    Phil Brown writes:

    >> Hi, did any of you try to calculate the tensions in a bike frame, for example using a finite
    >> element software? any web site?

    > Not much tension in a bike frame. Most loads are compressive.

    Having had involuntary research on this, I can say that the seat tube is in compression while
    sitting and tension while standing. I rode home sitting when the seat tube broke at the BB.
    Chainstays are in tension except the right one when pedaling hard. The larger diameter tubes also
    experience bending and torsion, something the "rear triangle" tubes do not (that's why they are
    thin.) Braking forces (bending) at the rear brake bridge are insignificantly small.

    Analyzing stresses in a bicycle frame is difficult because the human input is hard to model to a
    large degree and valid assumptions are difficult to make. A good method would be to instrument a
    bicycle ridden by a versatile rider to record loadings in frame elements of interest during various
    modes of use. Then an analysis for peak stresses could be made using these inputs. I believe this
    hasn't been done to any significant degree or we would have seen (promotional) reports of it.

    Jobst Brandt [email protected] Palo Alto CA
     
  4. Amerigo

    Amerigo Guest

    "Phil Brown" <[email protected]> ha scritto nel messaggio
    news:[email protected]...
    > >Hi, did any of you try to calculate the tensions in a bike frame, for example using a finite
    > >element software? any web site?
    >
    > Not much tension in a bike frame. Most loads are compressive. Phil Brown

    this can't be true, to have equilibrium in a node, the compression must be equilibrated by a tension
    anyway, the equilibrium of the nodal forces.. I wrote tension intending tension/compression
     
  5. Amerigo

    Amerigo Guest

    <[email protected]> ha scritto nel messaggio
    news:[email protected]...
    > Analyzing stresses in a bicycle frame is difficult because the human input is hard to model to
    > a large degree and valid assumptions are difficult to make. A good method would be to
    > instrument a bicycle

    yes, but I would like to calculate the ''magnitudo'' of the forces, for example in jumps

    > ridden by a versatile rider to record loadings in frame elements of interest during various modes
    > of use. Then an analysis for peak stresses could be made using these inputs. I believe this hasn't
    > been done to any significant degree or we would have seen (promotional) reports of it.

    yes, the bike is not enough studied by engineers, this is demonstrated by the quick release
    problem....
     
  6. Todd Kuzma

    Todd Kuzma Guest

    [email protected] wrote:

    > I believe this hasn't been done to any significant degree or we would have seen (promotional)
    > reports of it.

    I have seen color-coded plots of stresses on the frame in some advertising. However, after reading
    the accompanying text and seeing the design decisions made as a result of this information, I'm
    assuming that nobody at the company really understands the issues. I would not be surprised if the
    graphic was something that was created primarily for use in promotional materials rather than for
    the design process.

    Todd Kuzma Heron Bicycles Tullio's Big Dog Cyclery LaSalle, IL 815-223-1776
    http://www.heronbicycles.com http://www.tullios.com
     
  7. In article <[email protected]>, [email protected] wrote:
    >
    >I have seen color-coded plots of stresses on the frame in some advertising.

    Those were probably the results of some finite element analysis. Of course, any such computation
    would have required some input loads and boundary conditions be specified.

    If I understood Jobst correctly, his conjecture is that this area (determination of the inputs and
    bcs) has not been studied in any real or thorough fashion (riders and riding conditions, etc).

    It'd be interesting to see...

    cheers, john
     
  8. Dianne_1234

    Dianne_1234 Guest

    It's old, but there is one FEA report here: http://www.sheldonbrown.com/rinard/fea.htm

    [email protected] wrote in message news:<[email protected]>...
    > Phil Brown writes:
    >
    > >> Hi, did any of you try to calculate the tensions in a bike frame, for example using a finite
    > >> element software? any web site?
    >
    > > Not much tension in a bike frame. Most loads are compressive.
    >
    > Having had involuntary research on this, I can say that the seat tube is in compression while
    > sitting and tension while standing. I rode home sitting when the seat tube broke at the BB.
    > Chainstays are in tension except the right one when pedaling hard. The larger diameter tubes also
    > experience bending and torsion, something the "rear triangle" tubes do not (that's why they are
    > thin.) Braking forces (bending) at the rear brake bridge are insignificantly small.
    >
    > Analyzing stresses in a bicycle frame is difficult because the human input is hard to model to a
    > large degree and valid assumptions are difficult to make. A good method would be to instrument a
    > bicycle ridden by a versatile rider to record loadings in frame elements of interest during
    > various modes of use. Then an analysis for peak stresses could be made using these inputs. I
    > believe this hasn't been done to any significant degree or we would have seen (promotional)
    > reports of it.
    >
    > Jobst Brandt [email protected] Palo Alto CA
     
  9. Amerigo

    Amerigo Guest

  10. "Not much tension in a bike frame. Most loads are compressive. Phil Brown "

    Excuse me, I'm don't have any degrees in engineering or anything, but wouldn't the down tube be
    under tension?

    May you have the wind at your back. And a really low gear for the hills! Chris

    Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner
     
  11. <[email protected]> wrote in message news:EDZw[email protected]...
    > Analyzing stresses in a bicycle frame is difficult because the human input is hard to model to a
    > large degree and valid assumptions are difficult to make. A good method would be to instrument a
    > bicycle ridden by a versatile rider to record loadings in frame elements of interest during
    > various modes of use. Then an analysis for peak stresses could be made using these inputs. I
    > believe this hasn't been done to any significant degree or we would have seen (promotional)
    > reports of it.

    I agree that the process being described is difficult - and I am glad, because if it wasn't I
    wouldn't have a career. However, bicycle instrumentation has been done in the past.

    Cannondale did instrumentation back when I was in the industry - I set the test specification for a
    disc brake testing protocol with the help of their fork strain gage data.

    The current crop of powermeters (SRM, Powertap, Polar) instrument various parts of the bicycle in
    order to calculate torques.

    Tour magazine has published articles in which they have instrumented handlebars/forks.

    The AIS has also used instrumentation in their track bike development programs.
    (http://tinyurl.com/bzn0).

    Academia is full of professors with bike instrumentation projects (http://tinyurl.com/bzn7).

    Heck, even I instrumented my bike a couple of years ago (http://tinyurl.com/7o9q) - pretty lame
    attempt, but hey, it seemed to work out OK for the purpose.

    --
    ==================
    Kraig Willett www.biketechreview.com
    ==================
     
  12. Todd Kuzma

    Todd Kuzma Guest

    Chris Zacho The Wheelman wrote:
    > I would think that this has been done, in fact, it mustr have been. Consider, that in building a
    > carbon fiber monocoque (one piece) frame in which the fibers are layed directional to the force
    > loads, those loads would have to be known, wouldn't they?

    I wouldn't assume this. They could be using the "best guess" method of determining loads. If a
    number of bicycle designers don't understand the effect of oval tubing in bicycle frames, what makes
    you think that they would understand how to lay carbon fiber?

    Todd Kuzma Heron Bicycles Tullio's Big Dog Cyclery LaSalle, IL 815-223-1776
    http://www.heronbicycles.com http://www.tullios.com
     
  13. Todd, what method do you use to design your frames?

    --
    ==================
    Kraig Willett www.biketechreview.com
    ==================
     
  14. I wasn't really going anywhere - just curious, and since you are representing your brand, figured
    you would be intimate with the product development process of your bikes. I am always interested in
    how people make and validate their parts. So that it is perfectly clear (in my mind, at least - if
    that is possible), your company doesn't do analysis/testing on any of it's new products?

    How intimate are you with the manufacturers product development/engineering process that you are
    being critical of?

    Who _exactly_ are you upset with?

    --
    ==================
    Kraig Willett www.biketechreview.com
    ==================
     
  15. Todd Kuzma

    Todd Kuzma Guest

    Kraig Willett wrote:
    > I wasn't really going anywhere - just curious, and since you are representing your brand, figured
    > you would be intimate with the product development process of your bikes. I am always interested
    > in how people make and validate their parts. So that it is perfectly clear (in my mind, at least -
    > if that is possible), your company doesn't do analysis/testing on any of it's new products?

    I wouldn't say that is true. For example, when the first Herons were introduced, they came with a
    fork crown that used round blades rather than oval blades. This fork was fatigue tested in
    accordance with DIN and ISO standards. However, since the rest of the frame design was not straying
    very far from what had been done for some time, no testing was required.

    > How intimate are you with the manufacturers product development/engineering process that you are
    > being critical of?
    >
    > Who _exactly_ are you upset with?

    Do a search of the many discussions on rec.bikes.tech about ovalized tubing or carbon stays. There
    are lots of examples. One good example is Lemond bicycles. I love this stuff from their website:

    "3/2.5 Titanium Alloy: We choose 3/2.5 over 6/4 because we can mechanically butt to minimize the
    weight and tune the response you feel from the ride."

    or

    "Shaping tubing: The down tube is ovalized at the bottom bracket to be laterally stiff under pedal
    loads and vertically compliant to road shock. The top tube is ovalized at the seat tube to isolate
    the rider's weight while the round sections absorb road shock."

    Now, let me ask you, is this stuff driven by the engineers (who then apparently really don't
    understand the issues) or by the marketing folks (who then apparently are driving the design work)?

    Todd Kuzma Heron Bicycles Tullio's Big Dog Cyclery LaSalle, IL 815-223-1776
    http://www.heronbicycles.com http://www.tullios.com
     
  16. "Todd Kuzma" <[email protected]> wrote in message news:[email protected]...
    > Kraig Willett wrote:
    > > I wasn't really going anywhere - just curious, and since you are representing your brand,
    > > figured you would be intimate with the product development process of your bikes. I am always
    > > interested in how people make and validate their parts. So that it is perfectly clear (in my
    mind,
    > > at least - if that is possible), your company doesn't do
    analysis/testing on
    > > any of it's new products?
    >
    > I wouldn't say that is true. For example, when the first Herons were introduced, they came with a
    > fork crown that used round blades rather than oval blades. This fork was fatigue tested in
    > accordance with DIN and ISO standards. However, since the rest of the frame design was not
    > straying very far from what had been done for some time, no testing was required.

    No testing is actually required, is it? I thought that it was up to the mfr's to be certain that the
    products they sell/spec are safe enough. When I was in the wheel biz, the big name bike mfr's had
    the most rigorous mechanical testing/qualification protocols - it was the little guys who spec'd
    stuff based only on a marketing/pricing sheet.

    > > How intimate are you with the manufacturers product
    development/engineering
    > > process that you are being critical of?
    > >
    > > Who _exactly_ are you upset with?
    >
    > Do a search of the many discussions on rec.bikes.tech about ovalized tubing or carbon stays. There
    > are lots of examples. One good example is Lemond bicycles. I love this stuff from their website:
    >
    > "3/2.5 Titanium Alloy: We choose 3/2.5 over 6/4 because we can mechanically butt to minimize the
    > weight and tune the response you feel from the ride."
    >
    > or
    >
    > "Shaping tubing: The down tube is ovalized at the bottom bracket to be laterally stiff under pedal
    > loads and vertically compliant to road shock. The top tube is ovalized at the seat tube to isolate
    > the rider's weight while the round sections absorb road shock."

    Thanks for the specifics, Todd.

    IMHO, these are vague product claims and should be recognized as such. If pressed, I believe they
    could, and more importantly _would_, stand up in court. The fact that the large company in question
    still makes these claims demonstrates they are confident in the result of such an attempt to
    prosecute. Based solely on the snippets provided, I would not come to the conclusion that the
    company behind them doesn't know what they are doing from an engineering/design standpoint.

    If these claims bother you so much, why don't you actually _do_ something about it besides complain
    on a public forum? I was skeptical of the whole carbon stay thing, too, and offered to arrange a
    double blind test for the manufacturer (I made the offer in one of my online articles, and the mfr
    in question subsequently scared my editor into removing the "scary" bits). I also did something when
    I saw some of the current stems that were being shipped - I mechanically tested them. In order to
    make sure that the stem results weren't edited out of the public eye, I started my own website (this
    wasn't a cheap project). I have learned a lot from the whole process (some of what I learned was
    actually related to engineering, too).

    > Now, let me ask you, is this stuff driven by the engineers (who then apparently really
    > don't understand the issues) or by the marketing folks (who then apparently are driving the
    > design work)?

    How would I know the specifics of how Lemond/Trek is organized?

    I _do_ know that Trek/LeMond has competent engineers, and to imply otherwise is, IMHO, disingenuous.

    --
    ==================
    Kraig Willett www.biketechreview.com
    ==================
     
  17. Todd Kuzma

    Todd Kuzma Guest

    in article [email protected], Kraig Willett at
    [email protected] wrote on 5/17/03 5:30 PM:

    > No testing is actually required, is it? I thought that it was up to the mfr's to be certain that
    > the products they sell/spec are safe enough.

    There is a difference between testing to ensure that products are safe and product development.
    Testing only requires a sound test protocol and the resources in order to carry out the testing.
    Product development requires much more.

    > Based solely on the snippets provided, I would not come to the conclusion that the company behind
    > them doesn't know what they are doing from an engineering/design standpoint.

    Oh? You have no problem with the claim that they "mechanically butt [sic]" the tubing "tune the
    response you feel from the ride?" Do you believe that their engineers designed the tubing to do this
    and were able to verify the results in a scientific manner? If so, why not show us how. Since they
    are making the claimm, they carry the burden of proof.

    They would have to define what they mean by "ride," show that they have the ability to affect it by
    varying wall thickness, and then show that the change in "ride" is significant enough to be
    noticeable by the rider.

    Their claims about their "shaped tubing" are even more ridiculous. They are merely copying the style
    of oversized aluminum frames which are ovalized purely for the purpose of being able to join tubes
    of different sizes. You aren't going to be able a 1.5" diameter tube to a 1.125" diameter tube
    without squishing the larger tube to fit. Of course, the aluminum manufacturers tried to turn this
    into a marketing advantage years ago by making similar claims.

    Still, let's take a look at what they say: "The down tube is ovalized at the bottom bracket to be
    laterally stiff under pedal loads and vertically compliant to road shock. The top tube is ovalized
    at the seat tube to isolate the rider's weight while the round sections absorb road shock."

    You don't need to be an engineer or have fancy test equipment to understand that the pedaling loads
    on the down tube are mostly torsional, not lateral. An ovalized tube will have LESS torsional
    stiffness than a round tube of equivalent size. But, hey, the horizontal ovalization makes it
    "vertically compliant" (despite the fact that a bicycle frame is an inherently stiff structure in
    the vertical plane) yet the vertical ovalization at the top tube doesn't seem to cancel that out.
    Instead, it isolates the rider's weight. What the hell does THAT mean?

    You and I both know that the ovalization of tubing here is done purely for marketing copy. If they,
    or any of the other companies who use similarly ovalized tubing, can provide some data to back up
    their claims, I'd like to see it.

    > If these claims bother you so much, why don't you actually _do_ something about it besides
    > complain on a public forum?

    If I had the resources to do so, I would. There are a number of folks who are making an effort to
    expand the knowledge base of our industry. Some have participated in the Hardcore Bicycle Science
    mailing list which unfortunately is no longer active. This list included a number of engineers and
    designers and was a fairly good exchange of ideas and information. Damon Rinard conducted a number
    of tests and published the results and most of his test protocols on his website (now on Sheldon
    Brown's site). I provided some wheels for his lateral wheel strength tests.

    Still, we can take what is already known about materials and design and apply them to the claims
    made by these companies. Many of the claims contradict what is generally accepted to be true. This
    does not automatically invalidate the claims, but it does place the burden on those making the
    claims to provide data to back them up. I have seen lots of claims and virtually no data.

    > I _do_ know that Trek/LeMond has competent engineers, and to imply otherwise is, IMHO,
    > disingenuous.

    I used to work in product management at Motorola and am quite familiar with engineers, engineering,
    and the product development process. Trek/Lemond may have engineers, but I'm not quite sure what it
    is that they do. Unlike engineers in other fields, they do not publish any of their research and
    their patent filings are quite limited. What has been filed lacks much engineering data.

    If the engineering were as competent as you suggest, I doubt that we would have seen the large
    number of OCLV failures over the years. That particular product development was tested by their
    customers and refined through feedback from the warranty department. Whatever engineering and
    testing they did was certainly inadequate in that case.

    Todd Kuzma Heron Bicycles LaSalle, IL http://www.heronbicycles.com/
     
  18. I stand by what I stated previously in the context I presented it.

    It appears to me as if you have some sort of axe to grind.

    Best of luck to you, Todd - you make nice looking bikes (and I mean that sincerely).

    --
    ==================
    Kraig Willett www.biketechreview.com
    ==================
     
  19. Todd Kuzma wrote:

    > Do a search of the many discussions on rec.bikes.tech about ovalized tubing or carbon stays. There
    > are lots of examples. One good example is Lemond bicycles. I love this stuff from their website:
    >
    > "3/2.5 Titanium Alloy: We choose 3/2.5 over 6/4 because we can mechanically butt to minimize the
    > weight and tune the response you feel from the ride."

    Hmm, wonder how one could butt a tube _other_ than mechanically. Perhaps by magic, or the
    power of faith?

    > "Shaping tubing: The down tube is ovalized at the bottom bracket to be laterally stiff under pedal
    > loads and vertically compliant to road shock. The top tube is ovalized at the seat tube to isolate
    > the rider's weight while the round sections absorb road shock."
    >
    > Now, let me ask you, is this stuff driven by the engineers (who then apparently really
    > don't understand the issues) or by the marketing folks (who then apparently are driving the
    > design work)?

    If I may play devil's advocate here, certainly that advertising copy is unadulterated post-consumer
    hay, but that doesn't mean that there's no reason for ovalizing tubes.

    On frames that use large diameter tubes, the junctions can get rather crowded. F'rinstance, fitting
    an oversized seat tube and an oversized down tube to a standard bottom bracket shell is nearly
    impossible if you keep them round.

    Some earlier Cannondales had very fat round downtubes, before the move to oversized steerers. The
    resulting frames, with a downtube larger than the head tube, had very ugly looking downtube/headtube
    junctions.

    If the marketeers were to say "we had to squish the oversized tubes to make them fit together that
    probably wouldn't sell many bikes, so they make up this taurine excrement instead, relying on the
    old adage "You can fool some of the people all of the time--and those are the ones we're after!"

    Sheldon "Making A Virtue Of A Necessity" Brown +--------------------------------------------+
    | To see what is in front of one's nose | needs a constant struggle | --George Orwell |
    +--------------------------------------------+ Harris Cyclery, West Newton, Massachusetts Phone
    617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts shipped Worldwide
    http://captainbike.com http://sheldonbrown.com
     
  20. Todd Kuzma

    Todd Kuzma Guest

    Kraig Willett wrote:
    > I stand by what I stated previously in the context I presented it.
    >
    > It appears to me as if you have some sort of axe to grind.

    Sure I have an axe to grind. It's companies that use BS to sell their products. That's what we are
    talking about here: BS that masqerades as "engineering." Unfortunately, a lot of folks believe this
    BS. So, the companies who don't use BS are put at a disadvantage in the marketplace.

    So, how does a non-BS-using company combat this disadvantage? If you try to point out that what
    these companies are selling is actually BS, folks line up to say that you are jealous and have an
    axe to grind.

    Todd Kuzma Heron Bicycles Tullio's Big Dog Cyclery LaSalle, IL 815-223-1776
    http://www.heronbicycles.com http://www.tullios.com
     
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