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  1. #1
    Weakling
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    Geometry and dynamics of frames?

    I know nothing of such so i looked in Wikipedia.
    http://en.wikipedia.org/wiki/Bicycle...cycle_dynamics

    so far so good but whoa that txt is way too abstract for a poor soul like me.

    Do you know of a text that are more easy to grasp while still taking up
    same dynamics and hopefully from a Do It Yourself point of view.

    I remember vaguely that a Dutch recumbent builder tried to explain
    which angles worked best for him. But I am trying to plan to build
    a stronger version of Carryme bike from Pacific Cycles in Taiwan.

    That bike is build for lighter and not so tall people as I am.
    I weight 210lb so that is too heavy and me is 6'4" 1940mm
    so that makes me too tall. My knees would bump into steering and
    knock me out of balance in critical moment in buisy traffic streets.

    While I am at it I need to learn the dynamics of how to build a good bike.

    I saw an impressive video at the wikipedia article.
    http://www.tam.cornell.edu/~ad29/JBike6/JBike6_self_stable_files/bicycle_stability.mpeg

    But they didn't say anything about the angles that bike had.

  2. #2
    weirdo
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    Quote Originally Posted by Weakling View Post
    I know nothing of such so i looked in Wikipedia.
    http://en.wikipedia.org/wiki/Bicycle...cycle_dynamics

    so far so good but whoa that txt is way too abstract for a poor soul like me.

    Do you know of a text that are more easy to grasp while still taking up
    same dynamics and hopefully from a Do It Yourself point of view.
    Wow- that does sound complicated. I`m in the same boat as you, but here`s one that puts it a little more simply:
    http://www.anvilbikes.com/?news_ID=49&catID=3
    It doesn`t go into much detail, but I guess that`s the price we have to pay for not wanting to spend years studying.

  3. #3
    Weakling
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    Thanks that text was much more practical.

    One problem is this. Looking at a bike picture.

    how to estimate if it is steeper in angle and so on
    compared to another bike one are interested in.

    One need to have them together in one place (shop)
    so one could test them within minutes so the body's
    memory don't adjust to one of them and then get
    confused hours or days later riding the other bike.

    Several here are very satisfied with how Strida handle itself.
    Others here like me admit it took minutes to adjust to it and
    not ten seconds as the other claim.

    Some complain about how the Mobiky rides. Should I trust them?
    Maybe they compare Mobiky to a standard bike and not compare it
    to Strida.


    Suppose Strida is the less ordinary in geometry and it to be way
    outside the figures in the anvil text. Then it would be handy to
    have figures for Strida and Mobiky and Tikit and Dahon and Downtube
    and Brompton and A-bike and Carryme all the other folders so one
    knows how they compare with each other.

    Measurement are less subjective than personal experience of a single folder.

    I would trust the bad report on a Mobiky if they had compared it with a Strida
    tested the same half hour.


    Steedman Bass the CEO of Strida insisted they use unexperienced riders when they
    finetuded the Strida III to be better handling than the Strida II that some have complained
    to be hard to learn. And the Strida III are easier to learn to adjust to.

    For most people it happens so fast that they needed to change to new non-experienced
    test riders cause the one already got used to it and could not give reliable report on how
    it behaved.

    I think it shows how utterly subjective such personal experiences are.

    Measured figures should be more reliable. so could some friendly soul
    measure a Strida and a Mobiky. I live so so far away from that shop so I could only
    visit it next fortnight at high cost for the neighbor letting me lift in his car.
    Last edited by Weakling; 02-09-08 at 06:16 AM.

  4. #4
    Banned
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    Fundamentally though, your extra weight and height do not require changes in geometry, just scaling up the bike you are looking at. If in addition to that you want to make other changes, that is a different mater.

    Most bikes are going to work pretty well if they combine a correct geometry for you to pedal efficiently on with a reasonable steering geometry. Stearing geometry is a combination of head tube angle and trail. From a practical design perspective you will find a lot of bikes share indentical, or very similar numbers where trail is comcerned, since the head tube angles and the forks used are similar per type. For instance on racing bikes or MTBs the forks are often separately sourced, and the head tube angles within a narrow range. All you have to do is learn the applicable head tube agle, the fork offset, and the resultant trail for the kinds of bike you are interested in. These relationships are easily drawn in cad or by hand, and there are computer calculators online. Then you can consider if you have a particular design that needs to diverge from the norm for some reason.

    Folding bikes are difficult because folding imposes some design needs that can take the bike out of ideal numbers in other regards. If I was interested in folding designs I would enter pics into my cad program and draw simple geometric models of the different designs that interest me, and figure out what makes them tick.

    Beyond these basics every model will have performance attributes like wheel base, degree the rear wheel is tucked, all maner of things. But any active cyclist probably already has some ideas of those features.

  5. #5
    Weakling
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    Thanks Peter,

    I measured my old Microbike and it is slightly bigger than the Carryme.
    Unfortunately for me the Carry me is just too small. It looks very certain
    that my knee will hit my hands or the handles when I make turns and
    even when I go stright forward.

    I adjusted my Microbike to be as close to a Carryme in height of handlebar
    but mine is still some two inches taller from ground up. So my hands will get
    in the way when my knee is at it's most high position on the Carryme while
    they are just enough clearance riding at theMicrobike.

    Unfortunately that one has not wheels to replace the old aging plastic
    which become brittle with age and usage. Like plastic boats the plastic
    catch plastic fever when more than 15 years old . the bike was built
    around 1987.
    when I told the designer about it he said he wouldn't risk his health
    riding on it. So I do it on my own risk. The kevlar belt is supposed to
    end up dead sooner or later too being so old and they are half width
    of standard so one need a very good saw to make two usable ones
    out of the standard kevlar belt sold in shops.

    So sooner or later me need to find something that is as good as
    the Mickrobike.

    I could try to put the saddle as far back as possible but then most likely
    I would make a wheely sorry if spelling is not correct.

    the frame of the Carryme is made for shorter people than me.

    So could I really build a longer version of the Carryme maybe.
    For some 250 Brittish Pounds or some 575 USD?

    I 'm so clumsy when it comes to mechanics. Carryme as a model
    seems to be the best design I've come upon. Weight only 8 kg.
    Foot print around 10" to 12" or so. That is what I like about it.

    What I don't like is that it has too small wheels. But it helps with
    making the footprint small.

    The alternative solution would be to build a trolly, trolley cart
    when it is folded. such are allowed in foodstores. Bikes are not.

    The trolley mostly have two wheels in parallel and that is ideal
    from a handling point of view. One fasten the basket for shopping
    between these wheels and that is a conveniant way to do shopping.

    One only have to come up with a practical design that allow it to happen.

    JZ88 seems to have that in mind. http://www.jz88.com/
    Last edited by Weakling; 02-09-08 at 05:01 PM.

  6. #6
    Weakling
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    Geometry and dynamics of frames?

    Compare Strida and Ezybike.




    Isn't the slant very much the same.

    but if we compare these two with
    my old Microbike and the new Carryme.
    don't they have very similar geometry and the slant similar.

    while the Strida and the Ezybike are the exceptions. Most bike
    are like the Carryme. They have similar slant wile Strida is extreme?

    Is that why Strida takes time to learn?

    I'm talking here about how they feel when riding. the angle determine
    how the bike handle itself. I don't talk about the difference in folding.



  7. #7
    Weakling
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    Here is how Strida Designer Mark Sander made his Strida. Drawings and thoughts and what features he needed.

    http://www.dezeen.com/2008/02/03/int...-mark-sanders/

  8. #8
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    If you look at the strida, it appears that a line drawn throught he turning axis/"headtube" angle actually passes above the axle, rather than below. A rather radical departure in geometery.

  9. #9
    Weakling
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    Peter, and he comment on it himself that this is true.

    citation from Mark Sanders

    http://stridasingapore.com/forum/ind...32&topic=364.0

    When Mark Steedman bought over the company, he was keen to perfect the Strida.
    And he wanted to improve its handling, so he consulted all the 'experts' in the industry who came up
    with various theories about what would improve the handling - and most suggested various angles
    and tweaks based on traditional theories, and most were wrong!

    We had a special fully adjustable test rig so we could try out the various theories and settings.

    This was harder than expected because of the lack of "Strida virgins" ... the human soon learns to
    adapt so the familiarity of the bike handling soon spoiled objectivity. In the end, we changed
    two key factors: 1. we added ball bearings to the main loadbearing (lower) joint

    2. we used the geometry settings from the rig most preferred by 'Strida virgins'.

    The steering geometry of a Strida (Strida 2.5) is now quite different from the theories,
    but it works! For a bike with such a short wheelbase, the handling is now really good,
    a well balanced rider can ride hands off (don't try this at home, folks!)"
    After that we have Strida 3.2 and Strida 5 so that has to be considered too.
    (Strida 3.6 has magnetic clips? while 3.2 only the plastic grips)

    I've only tested the Strida I and Strida 3.2 and the 3.2 is very much improved
    but I fail to say that it handle itself as good as Mark and Mark above says it does.

    I guess the 2.5 and 3.2 have same geometry. Steedman at Ming Cycles
    don't wont to change a winning design so most likely they have kept it.


    So that is why it don't live up to our expectations on the geometry.

    They first followed the book and it didn't work and then they made
    a test rig and changed it until it worked for new to the bike.

    So that is surprising. Why would the test riders chose a handling
    less than optimal?

    I wish me could buy a Strida that handles like normal bikes does.

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