Computer Program to calculate frame dimensions?

Discussion in 'Cycling Equipment' started by x, Apr 8, 2003.

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  1. x

    x Guest

    I've got a new harttail MTB frame that didn't work out so well...in fact the builder offered to
    build another one just for the cost of tubing and other parts to get it off the road (it has his
    name on it...).

    I've been riding it and have my adjusted my position to where it's tolerable but the problem I'm
    having measurement-wise is that when one thing changes, other things tend to change in unexpected
    ways. I'm afraid to say "just change

    else.

    I've got another frame (FS) that's pretty much dialed in - but on which I've got to use a 2" setback
    seatpost to get myself to KOPS.

    Seems like I should be able to measure all the dimensions on that frame, key them into a computer
    program, then try altering this or that dimension and have the program show me what else changes and
    by how much....or even tell the program to constrain certain dimensions....

    Anybody know of something in this line?
    -----------------------
    PeteCresswell
     
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  2. (Pete Cresswell) wrote:

    > I've got a new harttail MTB frame that didn't work out so well...in fact the builder offered to
    > build another one just for the cost of tubing and other parts to get it off the road (it has his
    > name on it...).
    >
    > I've been riding it and have my adjusted my position to where it's tolerable but the problem I'm
    > having measurement-wise is that when one thing changes, other things tend to change in unexpected
    > ways. I'm afraid to say "just change

    > else.
    >
    > I've got another frame (FS) that's pretty much dialed in - but on which I've got to use a 2"
    > setback seatpost to get myself to KOPS.
    >
    > Seems like I should be able to measure all the dimensions on that frame, key them into a computer
    > program, then try altering this or that dimension and have the program show me what else changes
    > and by how much....or even tell the program to constrain certain dimensions....
    >
    > Anybody know of something in this line?
    > -----------------------
    > PeteCresswell

    actualy frames have been built for so long that Nothing changes 'unexpectedly" for an
    *experienced* builder. my suggestion is you get a true frame builder to do the work not just some
    hack with a torch.
     
  3. x

    x Guest

    RE/
    >actualy frames have been built for so long that Nothing changes 'unexpectedly" for an
    >*experienced* builder. my suggestion is you get a true frame builder to do the work not just some
    >hack with a torch.

    I have no doubt that just about any builder is in full control as long as nobody's telling him
    what to do.

    The doubts I have grow around the builder's idea of what a proper fit is for me.

    The guy who did the first one is no hack - he's survived for over 20 years building frames and
    nothing else.

    I think two things were wrong. First, I tried to tell him too much and he followed my flawed
    instructions - rather than arguing with some lunatic that outweighs him by a factor of at least two,
    maybe three... Second, I don't think he's got a lot of experience with MTBs. (i.e. he didn't think
    about fork clearance in terms of those little adjustment knobs on the crown...)

    I've since tried to establish contact with a guy on the West Coast that makes a single-speed frame
    that others have given good reviews to. Racked up about a half hour of cell phone time after which
    he asked me to write an email.....Never got a reply...

    I *may* be back to just buying an off-the-shelf steel frame and having the S&S couplings
    retrofitted. Sure would be a lot cheaper.

    The two primary uses for this bike are:
    - To have a bike that I can store in my vehicle's rooftop box or in the trunk of a small-ish car
    and just sort of forget about until an unexpected riding opportunity arises
    - To function as a spare while the FS is offline for repair.

    But I need about two additional inches of setback to get KOPS on my FS and, I'm guessing, on any
    other off-the-shelf frame. That puts me back far enough to make the front end really light. Not a
    problem until you get to those grades where you're shifting weight back-and-forth balancing the
    tradeoff between the front wheel floating and the rear breaking traction - or where you're trying to
    zig-zag up a hill pedalling hard and the thing comes unglued just as you're laying into a turn.

    The "frame-gone-bad" that I'm riding now corrects that floaty front wheel and I think I like
    it....whether I like it enough to go through the process of another custom frame remains to
    be seen...
    -----------------------
    PeteCresswell
     
  4. Mark Hickey

    Mark Hickey Guest

    "(Pete Cresswell)" <[email protected]> wrote:

    >I've got a new harttail MTB frame that didn't work out so well...in fact the builder offered to
    >build another one just for the cost of tubing and other parts to get it off the road (it has his
    >name on it...).
    >
    >I've been riding it and have my adjusted my position to where it's tolerable but the problem I'm
    >having measurement-wise is that when one thing changes, other things tend to change in unexpected
    >ways. I'm afraid to say "just change

    >else.
    >
    >I've got another frame (FS) that's pretty much dialed in - but on which I've got to use a 2"
    >setback seatpost to get myself to KOPS.
    >
    >Seems like I should be able to measure all the dimensions on that frame, key them into a computer
    >program, then try altering this or that dimension and have the program show me what else changes
    >and by how much....or even tell the program to constrain certain dimensions....
    >
    >Anybody know of something in this line?

    Not online, but if you have a frame that's dialed in fit-wise, it's not too hard to convert the
    measurements to a new design.

    For example, if you can measure the relationship between the BB, the saddle and the bars, you can
    "draw a bike around those points". Here's where experience comes in - it's nice to know the effects
    of the different ways of making the bike fit those three points. For example, radically shortening
    the top tube might help get the cockpit length right, but you have to know how it will affect toe
    overlap with the front wheel, and handling, and weight distribution, etc.

    FWIW, when I'm designing custom frames for people with a frame that fits, I use a CAD program to lay
    down the three points, then draw the rest of the bike around them. I'm not aware of any online tool
    to do the same, but any CAD program (or even engineering graph paper) will suffice.

    Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame
     
  5. A Muzi

    A Muzi Guest

    "(Pete Cresswell)" <[email protected]> wrote in message news:[email protected]...
    > I've got a new harttail MTB frame that didn't work out so well...in fact
    the
    > builder offered to build another one just for the cost of tubing and other
    parts
    > to get it off the road (it has his name on it...).
    >
    > I've been riding it and have my adjusted my position to where it's
    tolerable but
    > the problem I'm having measurement-wise is that when one thing changes,
    other
    > things tend to change in unexpected ways. I'm afraid to say "just change

    something
    > else.
    >
    > I've got another frame (FS) that's pretty much dialed in - but on which
    I've got
    > to use a 2" setback seatpost to get myself to KOPS.
    >
    > Seems like I should be able to measure all the dimensions on that frame,
    key
    > them into a computer program, then try altering this or that dimension and
    have
    > the program show me what else changes and by how much....or even tell the program to constrain
    > certain dimensions....

    I do not but it is not at all difficult or time consuming to draw a bicycle frame. Perhaps you might
    do a few drawings with relevant items at various values and compare the results?

    --
    Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
     
  6. Kbh

    Kbh Guest

    I have one that I made while agonizing over my newest road bike, I'll put it here:

    www.hollasch.com/bike_geometry.xls

    It is by no means a polished piece of work, nor do I guarantee its accuracy. Nonetheless, it is
    quite exhaustive, allowing you to input pretty much any dimension and angle you could think of on a
    bike, and it outputs the relative position between the handlebars and seat (the original reason I
    made it), as well as standover height, saddle setback, wheelbase, front-center, and trail. Its based
    on an X,Y coordinate system that is 0,0 at the point on the ground directly below the bottom
    bracket, and uses a whole lot of high school geometry (I think if my high school geometry teacher
    saw this he would cry).

    Note that there are roll-over notes on many of the cells which explain what they are.

    Have fun and let me know what you think.

    Kyle

    "A Muzi" <[email protected]> wrote in message news:[email protected]...
    > "(Pete Cresswell)" <[email protected]> wrote in message news:[email protected]...
    > > I've got a new harttail MTB frame that didn't work out so well...in fact
    > the
    > > builder offered to build another one just for the cost of tubing and
    other
    > parts
    > > to get it off the road (it has his name on it...).
    > >
    > > I've been riding it and have my adjusted my position to where it's
    > tolerable but
    > > the problem I'm having measurement-wise is that when one thing changes,
    > other
    > > things tend to change in unexpected ways. I'm afraid to say "just
    change

    > something
    > > else.
    > >
    > > I've got another frame (FS) that's pretty much dialed in - but on which
    > I've got
    > > to use a 2" setback seatpost to get myself to KOPS.
    > >
    > > Seems like I should be able to measure all the dimensions on that frame,
    > key
    > > them into a computer program, then try altering this or that dimension
    and
    > have
    > > the program show me what else changes and by how much....or even tell
    the
    > > program to constrain certain dimensions....
    >
    >
    > I do not but it is not at all difficult or time consuming to draw a
    bicycle
    > frame. Perhaps you might do a few drawings with relevant items at various values and compare the
    > results?
    >
    > --
    > Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971
     
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