how to measure seat/headtube angles

Discussion in 'Cycling Equipment' started by Gerrit Van Wijk, Jun 29, 2003.

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  1. How can I measure my seat and headtube angles?
     
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  2. Jay Hill

    Jay Hill Guest

    gerrit van wijk wrote:
    > How can I measure my seat and headtube angles?
    >
    I suspect this will cause some protracted discussion...
     
  3. gerrit-<< How can I measure my seat and headtube angles? >><BR><BR>

    A good bike shop should have devices to do this. Get the top tube level, then use the inclinometer
    to measure head and seat tube.

    Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
    (303)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"
     
  4. Robin Hubert

    Robin Hubert Guest

    "Qui si parla Campagnolo" <[email protected]> wrote in message
    news:[email protected]...
    > gerrit-<< How can I measure my seat and headtube angles? >><BR><BR>
    >
    > A good bike shop should have devices to do this. Get the top tube level,
    then
    > use the inclinometer to measure head and seat tube.
    >

    On some bikes this will yield strange results (think compact). Heck, even on so-called horizontal
    top tube frames, as Jobst has mentioned, top tubes aren't usually horizontal.

    Wouldn't the best way be to get the dropouts horizontal, and then use an inclinometer?

    --
    Robin Hubert <[email protected]
     
  5. machinist protractor with bubble level is one option

    On Fri, 27 Jun 2003, gerrit van wijk wrote:

    > How can I measure my seat and headtube angles?
    >
    >
    >
    >
     
  6. gerrit van wijk wrote:
    > How can I measure my seat and headtube angles?

    The seat tube angle is easy if you have a horizontal top tube.

    Drop a plumb line from the top tube which intersects the centre of the BB shell. Measure two of the
    three sides of the triangle you have created (the long lengths are better for this as any
    inaccuracies have less effect on the result). The top tube to plumb line angle is 90 degrees, so a
    little trigonometry will then give you the seat tube angle.

    --
    R.

    <> Richard Brockie "Categorical statements <> The tall blond one. always cause trouble." <>
    [email protected]
     
  7. Qui si parla Campagnolo wrote:
    > Robin-<< Wouldn't the best way be to get the dropouts horizontal, and then use an inclinometer?
    > >><BR><BR>
    >
    > Most horizontal dropouts aren't parallel to the ground tho, the angle up a little toward the back
    > of the bike.
    >
    > Could check the level of the ground, then adjust the angles you see on said inclinometer...

    I think Robin meant to get the line between the front and rear dropouts level.

    --
    R.

    <> Richard Brockie "Categorical statements <> The tall blond one. always cause trouble." <>
    [email protected]
     
  8. Phil Brown

    Phil Brown Guest

    >Drop a plumb line from the top tube which intersects the centre of the BB shell. Measure two of the
    >three sides of the triangle you have created (the long lengths are better for this as any
    >inaccuracies have less effect on the result). The top tube to plumb line angle is 90 degrees, so a
    >little trigonometry will then give you the seat tube angle.

    Sorry, the top tube/plumb line intersection is not necessarily a right angle. In fact I would be
    surprised if it was. A degree or two slope in the surface the bike is resting on will throw all your
    calculations into a cocked hat. And how are you going to measure the lengths? Intersection of the
    tube. Very hard to get that accurate. Why not just use a protractor? And if you can't get a
    protractor in the space make up an angle and use the protractor to measure that. Phil Brown
     
  9. There is a neat (did I really say that?) little carpenter's devise which consists of a wood handle
    and a metal "blade" used for measuring and making angles. Any one here who knows what it's called
    gats a "no-prize".

    Use that against the top tube and the tube you wish to measure.

    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
     
  10. Scic

    Scic Guest

    >From: [email protected]

    >. Any one here who knows what it's called gats a "no-prize".

    It's called a sliding bevel square.

    Sig Chicago
     
  11. Phil Brown wrote:
    >>Drop a plumb line from the top tube which intersects the centre of the BB shell. Measure two of
    >>the three sides of the triangle you have created (the long lengths are better for this as any
    >>inaccuracies have less effect on the result). The top tube to plumb line angle is 90 degrees, so a
    >>little trigonometry will then give you the seat tube angle.
    >
    >
    > Sorry, the top tube/plumb line intersection is not necessarily a right angle. In fact I would be
    > surprised if it was. A degree or two slope in the surface the bike is resting on will throw all
    > your calculations into a cocked hat. And how are you going to measure the lengths? Intersection of
    > the tube. Very hard to get that accurate. Why not just use a protractor? And if you can't get a
    > protractor in the space make up an angle and use the protractor to measure that. Phil Brown

    Have you attempted this? If you did, you would see that it is relatively easy to do. The length of
    the tubes can be measured centre to centre to within a couple of mm by eye with a tape measure. In
    my case, 2/620 is an error which is <0.5% - small enough to be unimportant. Even for a small frame,
    this only grows to around 0.5%.

    I have compared my technique to the specs of frames from, I think, three different manufacturers and
    come close enough for my needs in all cases (within ~0.2° of the spec).

    --
    R.

    <> Richard Brockie "Categorical statements <> The tall blond one. always cause trouble." <>
    [email protected]
     
  12. [email protected] (Scic) Wrote:

    >From: [email protected]

    >Any one here who knows what it's called gats a "no-prize".

    >It's called a sliding bevel square.

    >Sig

    >Chicago

    Congratulations (and thanks). Here's your "no-prize". (don't spend it all in one place!) ;-3)

    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
     
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