sugg. for frame torsional stiffness test

Discussion in 'Cycling Equipment' started by Spacey Spade, Apr 26, 2003.

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  1. Spacey Spade

    Spacey Spade Guest

    Moved over from rec.bicycles.soc:

    >>>Dear Sheldon Brown,
    >>>
    >>>Thank you so much for your web pages devoted to cycling.
    >>>
    >>>I would very much like to see a torsional test on bicycle frames where the frame is held by the
    >>>wheel axles, and the deflection measurements are at the bottom bracket due to loads on the bottom
    >>>bracket. [paragraph cut, continued below]
    >>
    >>Then you would like to see Bicycling magazine's frame test jig, AKA "the tarantula". Back in the
    >>1980's, when Gary Klein and then Canondale were becoming popular, Bicycling published BB
    >>deflection for all bikes and frames they tested. Now they assume the readers are illiterate, so
    >>bike tests have lots of pictures, few words, and fewer numbers. You might get more info on
    >>rec.bicycles.tech, this topic seems to be more suited for that group. Mitch.
    >
    >Unfortunately Bicycling Magazine no longer tests bicycles. Now days they only publish puff pieces
    >or thinly veiled press releases. They don't want to pissoff their advertisers with any level of
    >criticism. Ken
    >
    >>>This would be a simple simulation for in-saddle hammering (when arms are not used). Is there some
    >>>test results published already?
    >>>
    >>>For the test you could use a 1" steel bar in the steerer as in a previous test of yours, making
    >>>sure to afix the bar on the axis where the front axle would be (and not allowing it to rotate
    >>>there, but allowing rotation in the steerer tube... either that or use the same forks on all
    >>>frames hehe!). You could even put weights on the saddle and on the handlebars to make it even
    >>>more lifelike.
    >>>
    >>>Having owned a Schwinn Premis, now a Cannondale, I really appreciate the torsional stiffness from
    >>>the Cannondale. On the Schwinn I used to look down and see the bottom bracket swinging from side
    >>>to side under load (and the chainring would rub the front derailleur to the same tune if I didn't
    >>>have it adjusted right). Spacey

    Would anyone with access to bikes be interested in doing some non-destructive tests?

    Regards,

    Spacey
     
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  2. Jon Isaacs

    Jon Isaacs Guest

    >Would anyone with access to bikes be interested in doing some non-destructive tests?
    >
    >Regards,
    >
    >Spacey
    >

    A few years ago Damon Rinard tested quite a few frames for out of plane stiffness.

    http://www.sheldonbrown.com/rinard/rinard_frametest.html

    >>>>I would very much like to see a torsional test on bicycle frames where the frame is held by the
    >>>>wheel axles, and the deflection measurements are at the bottom bracket due to loads on the
    >>>>bottom bracket. [paragraph cut, continued below]

    Actually the bottom bracket loads of interest are not reacted front wheel but rather between the
    rear wheel, the seat post/seat tube and the handle bars.

    If you are standing alongside the bike and push on the crank arm, then the fork will be under load
    but when riding it, the rider either pulls on the bars and pushes sideways on the seat.

    This is why Damon did not test the lateral stiffness of the fork in this particular test.

    jon isaacs
     
  3. Spacey Spade

    Spacey Spade Guest

    [email protected] (Jon Isaacs) wrote:
    > >Would anyone with access to bikes be interested in doing some non-destructive tests?
    > >
    > >Regards,
    > >
    > >Spacey
    >
    > A few years ago Damon Rinard tested quite a few frames for out of plane stiffness.
    >
    > http://www.sheldonbrown.com/rinard/rinard_frametest.html

    You know, I had looked over this previously and thought the figures showed forces applied in plane
    with the bicycle. I thought that was a little retarded myself. Oops, I guess I'm the retard.

    Anyway, too bad no one has done tests on the recent frames (or maybe someone has?).

    > >>>>I would very much like to see a torsional test on bicycle frames where the frame is held by
    > >>>>the wheel axles, and the deflection measurements are at the bottom bracket due to loads on the
    > >>>>bottom bracket. [paragraph cut, continued below]
    >
    > Actually the bottom bracket loads of interest are not reacted front wheel but rather between the
    > rear wheel, the seat post/seat tube and the handle bars.
    >
    > If you are standing alongside the bike and push on the crank arm, then the fork will be under load
    > but when riding it, the rider either pulls on the bars <interrupt>

    True, but I was refering to "in the saddle" simulation, and sometimes my hands are next to the stem
    with my fingers stretched out. Mostly my hands gently keep the front wheel going straight (the front
    wheel sways if you hammer no-hands).

    > </interrupt> and pushes sideways on the seat.

    This is negligible, or my butt would be really chaffed. I could also move my torso back and forth to
    keep balance on the seat while hammering. I tell you what... I'll ride on a mini-hammock for you
    (strung out along the plane of the bicycle). With my torso swaying I'll learn to keep the hammock
    from swaying ;)

    > This is why Damon did not test the lateral stiffness of the fork in this particular test.

    Hmmm... I guess a 1" steel rod would be the way to go since I bet forks have more give compared to
    the frame. The rod would have to be afixed with the same degrees of freedom as the forks though.
    Anyway, the main opposing out-of-plane forces to pushing down on the cranks (considering butt-seat
    out of plane forces negligible) come from the contact on the road.

    Regards,

    Spacey
     
  4. John McGraw

    John McGraw Guest

    I would love to see stems & handle bars tested by mounting them in a rigid jig & applying increasing
    loads & measuring deflection until destruction, paying particular attention to the mode of final
    failure. I would also like to see chain & chain lube tests by setting up a series of chainrings,
    rear cogs, front & rear derailers with ~1/2 hp electric motor driving them @ ~100rpm. One could use
    air to shift the derailers. Also set up h2o sprayers for wet testing & dust sprayers for dry
    testing. Surly someone must have done this. BTW Bicycling got rid of the tarantella over 10 yrs ago
    if memory serves, w/ some bs explanation like it was no longer relevant. They also had a device that
    w/ ~ a 70-lb weighted flywheel to test brakes. It could also be used to test cables & housings. I
    wonder if any lives that could have been saved? I believe that anyone buying anything has a right to
    know it's performance parameters. Such as how long will a given model of a chain last under a given
    set of circumstances. Or how long a certain chain lube will last in, say, wet conditions.

    [email protected] (Spacey Spade) wrote in message
    news:<[email protected]>...
    > [email protected] (Jon Isaacs) wrote:
    > > >Would anyone with access to bikes be interested in doing some non-destructive tests?
    > > >
    > > >Regards,
    > > >
    > > >Spacey
    > >
    > > A few years ago Damon Rinard tested quite a few frames for out of plane stiffness.
     
  5. On Mon, 28 Apr 2003 03:00:56 +0000, John McGraw wrote:

    > I would also like to see chain & chain lube tests by setting up a series of chainrings, rear cogs,
    > front & rear derailers with ~1/2 hp electric motor driving them @ ~100rpm. One could use air to
    > shift the derailers. Also set up h2o sprayers for wet testing & dust sprayers for dry testing.
    > Surly someone must have done this.

    Sadly, I see no reason to believe someone has done this. For one thing, chains are marketed at
    either shops, or the miniscule market of those consumers who care. Shops want a reasonable service
    life at a low price, and that is pretty well what most chains give. There is little change in design
    (since they got rid of the bushings, which is not an improvement except in cost of manufacture), and
    nothing viewed worthy of testing.

    Those who market to consumers spend hundreds of dollars in marketing hype for every penny in product
    development, so have no interest in testing. Since all the miracle lubes are basically variants on
    the same few ingredients, to test them only points out that they do not have the magical qualities
    they claim.

    What would be needed is a Consumer-Reports type of organization to buy and test equipment
    independently. But there is no money for that. The tests that Damon Rinard and others have done are
    a service to the community, but we can't expect them to do so extensively.

    --

    David L. Johnson

    __o | The lottery is a tax on those who fail to understand _`\(,_ | mathematics. (_)/ (_) |
     
  6. Spacey Spade

    Spacey Spade Guest

    [email protected] (Jon Isaacs) wrote in message
    news:<[email protected]>...
    > >True, but I was refering to "in the saddle" simulation, and sometimes my hands are next to the
    > >stem with my fingers stretched out. Mostly my hands gently keep the front wheel going straight
    > >(the front wheel sways if you hammer no-hands).
    >
    > >> </interrupt> and pushes sideways on the seat.
    > >
    > >This is negligible, or my butt would be really chaffed. I could also move my torso back and forth
    > >to keep balance on the seat while hammering. I tell you what... I'll ride on a mini-hammock for
    > >you (strung out along the plane of the bicycle). With my torso swaying I'll learn to keep the
    > >hammock from swaying ;)
    >
    > Look at a free body diagram of the rider. When the rider pushes on the pedal, those moments are
    > reacted either by the bars or by the seat post, there are no other options.

    With static forces, what you say is true. Considering dynamics are involved, things get more
    complicated. A spinning top doesn't fall over, even though it is leaning. I guess you don't spin
    your wheels fast enough LOL. My opinion is that the force on the seat perpendicular to the plane of
    the bicycle is less important when considering torsional stiffness of the frame (at the bottom
    bracket). That said, it wouldn't hurt to put something up against the seat so that it cannot flex
    out of the plane of the bicyle during the tests, but the setup would be best having the front and
    rear axles fixed as I described earlier(thanks for the input).

    > >Hmmm... I guess a 1" steel rod would be the way to go since I bet forks have more give compared
    > >to the frame. The rod would have to be afixed with the same degrees of freedom as the forks
    > >though.
    >
    > Draw a freebody diagram of the bicycle under pedalling forces. The fork does not enter the
    > situation.

    The front triangle does enter the picture in keeping the bottom bracket in place. Look at the Rinard
    testing: the front triangle was also tested for stiffness. Where was the weight placed for best
    "real life" experimenting? Where the axle of the front fork would be (and a 1" steel bar was used
    instead of a fork).

    > >Anyway, the main opposing out-of-plane forces to pushing down on the cranks (considering
    > >butt-seat out of plane forces negligible) come from the contact on the road.
    >
    > Draw the freebody diagram. Look at the the pedalling forces applied by the rider.
    >
    > When the rider pushes on the pedal, he/she needs to pull or push on something to counter the
    > lever arm of the pedal in the out of plane direction or the rider will just push the bike over on
    > its side.
    >
    > There are only two options, the handle bars and the seat. These are the only two other places the
    > rider contacts the bicycle.

    Leave the handlebars out if it for now. The out-of-plane forces on the tires will be equal and
    opposite to the force on the saddle. My concern is that the bottom bracket and two hubs be kept in
    the plane of the bicycle as much as possible (assume you are perfect at keeping the steering
    straight).

    > Add the forces applied by the chain and these you have the out of plane forces on the bike.

    Keep the chain as an internal stress in your FBD for simplicity's sake. I do, however, think that
    rear triangle stiffness is more important than front triangle stiffness (and I don't own a Kestrel).

    Spacey BSME
     
  7. Spacey Spade

    Spacey Spade Guest

    [email protected] (Jon Isaacs) wrote in message
    news:<[email protected]>...

    > >With static forces, what you say is true. Considering dynamics are involved, things get more
    > >complicated.
    >
    > I think it is relatively easy to show that pedalling a bicycle is quasi static, ie the frame is in
    > equalibrium with the pedalling forces at all times.
    [cut]

    The rider is moving. The rider is not in equilibrium. The rider has mass. The wheels are spinning.
    Sorry, I disagree.

    [cut]
    > If that is the case, then the frame cannot be artificially contrained by fixing the front and
    > rear axles.

    Not artificial.
     
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