Cycling Equipment · Public discussion

Frame dimensions misleading

Started by JS · · Last activity · 9 posts · 445 views

← Back to Cycling Equipment

Thread navigation

Jump through the discussion

Go to the original post, the replies on this page, or the latest preserved contribution.

01 / Original postFrame dimensions misleadingJS · 28 Jul 2005 02 / This pagePosts 1–9Page 1 of 1 · chronological order 03 / Latest replyPost #9Jeff Starr · 28 Jul 2005

Thread details

What we know about this thread

Original section
Cycling Equipment
Published
28 July 2005
Last activity
28 July 2005
Original author
JS
Posts
9
Discussion status
Public discussion
Total views
445
Views / 30 days
0
Topics
Titanium frames

The navigation and discussion metadata provide context. Posts remain in their original chronological order.

Showing posts 1–9 of 9
Posts remain in their original chronological order.

Text size
  1. Original post
    JS
    Archived post
    #1

    According to this website the "horizontal" top tube length "C" is greater
    than the top tube length c-c "D" which happens to be the sloping top tube
    length on this compact frame. Am I wrong, or is there something wrong with
    these dimensions? If we project two vertical lines from the center of the
    top/head tubes and seat/top tubes and measure the distance of "C', then that
    length has to be less than the sloping top tube length 'D".

    http://www.feltracing.com/05_frames/2005_sc1_frame.html

    look under 'geometry and specs'

    Thanks,
    John

    Report
  2. Vee
    Archived post
    #2
    JS said:

    According to this website the "horizontal" top tube length "C" is greater
    than the top tube length c-c "D" which happens to be the sloping top tube
    length on this compact frame. Am I wrong, or is there something wrong with
    these dimensions?

    The dimensions are (probably) right. The head tube and seat angles are
    different. It's hard to see from the picture.

    Quoted message said:

    If we project two vertical lines from the center of the
    top/head tubes and seat/top tubes and measure the distance of "C', then that
    length has to be less than the sloping top tube length 'D".

    Look at the "HA" and "SA" numbers. The seat tube angles back more than
    the head tube, so the vertical lines you talk about get farther apart
    as you move away from the top tube. It's easier to see why horizontal
    top tube is longer than the actual top tube on this page:
    http://www.lemondbikes.com/2005_bikes/geometry/spine_bikes.html

    -Vee

    Report
  3. JS
    Archived post
    #3

    I understand what's going on on that page and it makes perfect sense. The
    line projected from the seat tube on the Lemond page is not vertical. It
    runs parallel to the seat tube, whereas on the Felt page, it projects
    vertically, not parallel. Maybe, it's just poorly depicted.

    "Vee" <[email hidden]> wrote in message
    news:[email hidden]...

    Quoted message said:
    JS said:

    According to this website the "horizontal" top tube length "C" is


    greater

    Quoted message said:
    Quoted message said:

    than the top tube length c-c "D" which happens to be the sloping top


    tube

    Quoted message said:
    Quoted message said:

    length on this compact frame. Am I wrong, or is there something wrong


    with

    Quoted message said:
    Quoted message said:

    these dimensions?

    The dimensions are (probably) right. The head tube and seat angles are
    different. It's hard to see from the picture.

    Quoted message said:

    If we project two vertical lines from the center of the
    top/head tubes and seat/top tubes and measure the distance of "C', then


    that

    Quoted message said:
    Quoted message said:

    length has to be less than the sloping top tube length 'D".

    Look at the "HA" and "SA" numbers. The seat tube angles back more than
    the head tube, so the vertical lines you talk about get farther apart
    as you move away from the top tube. It's easier to see why horizontal
    top tube is longer than the actual top tube on this page:
    http://www.lemondbikes.com/2005_bikes/geometry/spine_bikes.html

    -Vee

    Report
  4. Mark Hickey
    Archived post
    #4
    JS said:

    According to this website the "horizontal" top tube length "C" is greater
    than the top tube length c-c "D" which happens to be the sloping top tube
    length on this compact frame. Am I wrong, or is there something wrong with
    these dimensions? If we project two vertical lines from the center of the
    top/head tubes and seat/top tubes and measure the distance of "C', then that
    length has to be less than the sloping top tube length 'D".

    http://www.feltracing.com/05_frames/2005_sc1_frame.html

    look under 'geometry and specs'

    There's nothing wrong with Felt's math.

    Think of it this way...

    You have two roughly parallel lines (head tube and seat tube).

    You want to draw a line between them. The shortest possible line will
    be perpendicular to the two original lines. Starting at the same
    point from the head tube, and angling the line up to horizontal will
    by necessity make that line (or, horizontal top tube) longer.

    I'm fairly well acquainted with this concept, having designed a LOT of
    frames with sloping top tubes... ;-)

    Mark Hickey
    Habanero Cycles
    http://www.habcycles.com
    Home of the $795 ti frame

    Report
  5. JS
    Archived post
    #5

    Nope sorry, but that's not what is being depicted in their diagram. The
    part that is misleading is the vertical line that is being projected from
    the seat tube. It needs to follow the same angle as the seat tube, not
    vertically. Simple geometry dictates that the line will be be shorter than
    the sloping line below it.

    "Mark Hickey" <[email hidden]> wrote in message
    news:[email hidden]...

    Quoted message said:
    JS said:

    According to this website the "horizontal" top tube length "C" is greater
    than the top tube length c-c "D" which happens to be the sloping top tube
    length on this compact frame. Am I wrong, or is there something wrong


    with

    Quoted message said:
    Quoted message said:

    these dimensions? If we project two vertical lines from the center of


    the

    Quoted message said:
    Quoted message said:

    top/head tubes and seat/top tubes and measure the distance of "C', then


    that

    Quoted message said:
    Quoted message said:

    length has to be less than the sloping top tube length 'D".

    http://www.feltracing.com/05_frames/2005_sc1_frame.html

    look under 'geometry and specs'

    There's nothing wrong with Felt's math.

    Think of it this way...

    You have two roughly parallel lines (head tube and seat tube).

    You want to draw a line between them. The shortest possible line will
    be perpendicular to the two original lines. Starting at the same
    point from the head tube, and angling the line up to horizontal will
    by necessity make that line (or, horizontal top tube) longer.

    I'm fairly well acquainted with this concept, having designed a LOT of
    frames with sloping top tubes... ;-)

    Mark Hickey
    Habanero Cycles
    http://www.habcycles.com
    Home of the $795 ti frame

    Report
  6. Mark Hickey
    Archived post
    #6
    JS said:

    Nope sorry, but that's not what is being depicted in their diagram. The
    part that is misleading is the vertical line that is being projected from
    the seat tube. It needs to follow the same angle as the seat tube, not
    vertically. Simple geometry dictates that the line will be be shorter than
    the sloping line below it.

    Look closely - although it's confusing, the diagram IS correct.

    The points those vertical lines start at are the same points you'd
    measure the top tube's actual and effective lengths. This is easly to
    imagine with the effective length measurement, since the vertical
    lines are perpendicular to the line being measured.

    It's not as obvious on the sloping top tube "actual" measurement, but
    as long as the vertical lines are the same length (they appear to be),
    and they start at the proper points (they do), the end result is the
    same as a measurement drawn between the measurement points themselves.

    The relationship between the lengths of the two lines isn't as obvious
    on a bike with such a shallow slope to the top tube (and that's
    probably why they offset the measurements as well, though if it were
    me I would have left the actual TT measurement centered on the top
    tube itself). Hey, wait... I did...
    http://www.habcycles.com/mtb.html

    Mark Hickey
    Habanero Cycles
    http://www.habcycles.com
    Home of the $795 ti frame

    Quoted message said:

    "Mark Hickey" <[email hidden]> wrote in message
    news:[email hidden]...

    Quoted message said:
    JS said:

    According to this website the "horizontal" top tube length "C" is greater
    than the top tube length c-c "D" which happens to be the sloping top tube
    length on this compact frame. Am I wrong, or is there something wrong


    with

    Quoted message said:
    Quoted message said:

    these dimensions? If we project two vertical lines from the center of


    the

    Quoted message said:
    Quoted message said:

    top/head tubes and seat/top tubes and measure the distance of "C', then


    that

    Quoted message said:
    Quoted message said:

    length has to be less than the sloping top tube length 'D".

    http://www.feltracing.com/05_frames/2005_sc1_frame.html

    look under 'geometry and specs'

    There's nothing wrong with Felt's math.

    Think of it this way...

    You have two roughly parallel lines (head tube and seat tube).

    You want to draw a line between them. The shortest possible line will
    be perpendicular to the two original lines. Starting at the same
    point from the head tube, and angling the line up to horizontal will
    by necessity make that line (or, horizontal top tube) longer.

    I'm fairly well acquainted with this concept, having designed a LOT of
    frames with sloping top tubes... ;-)

    Mark Hickey
    Habanero Cycles
    http://www.habcycles.com
    Home of the $795 ti frame


    Report
  7. Mark Hickey
    Archived post
    #7
    JS said:

    Nope sorry, but that's not what is being depicted in their diagram. The
    part that is misleading is the vertical line that is being projected from
    the seat tube. It needs to follow the same angle as the seat tube, not
    vertically. Simple geometry dictates that the line will be be shorter than
    the sloping line below it.

    Look closely - although it's confusing, the diagram IS correct.

    The points those vertical lines start at are the same points you'd
    measure the top tube's actual and effective lengths. This is easly to
    imagine with the effective length measurement, since the vertical
    lines are perpendicular to the line being measured.

    It's not as obvious on the sloping top tube "actual" measurement, but
    as long as the vertical lines are the same length (they appear to be),
    and they start at the proper points (they do), the end result is the
    same as a measurement drawn between the measurement points themselves.

    The relationship between the lengths of the two lines isn't as obvious
    on a bike with such a shallow slope to the top tube (and that's
    probably why they offset the measurements as well, though if it were
    me I would have left the actual TT measurement centered on the top
    tube itself). Hey, wait... I did...
    http://www.habcycles.com/mtb.html

    Mark Hickey
    Habanero Cycles
    http://www.habcycles.com
    Home of the $795 ti frame

    Quoted message said:

    "Mark Hickey" <[email hidden]> wrote in message
    news:[email hidden]...

    Quoted message said:
    JS said:

    According to this website the "horizontal" top tube length "C" is greater
    than the top tube length c-c "D" which happens to be the sloping top tube
    length on this compact frame. Am I wrong, or is there something wrong


    with

    Quoted message said:
    Quoted message said:

    these dimensions? If we project two vertical lines from the center of


    the

    Quoted message said:
    Quoted message said:

    top/head tubes and seat/top tubes and measure the distance of "C', then


    that

    Quoted message said:
    Quoted message said:

    length has to be less than the sloping top tube length 'D".

    http://www.feltracing.com/05_frames/2005_sc1_frame.html

    look under 'geometry and specs'

    There's nothing wrong with Felt's math.

    Think of it this way...

    You have two roughly parallel lines (head tube and seat tube).

    You want to draw a line between them. The shortest possible line will
    be perpendicular to the two original lines. Starting at the same
    point from the head tube, and angling the line up to horizontal will
    by necessity make that line (or, horizontal top tube) longer.

    I'm fairly well acquainted with this concept, having designed a LOT of
    frames with sloping top tubes... ;-)

    Mark Hickey
    Habanero Cycles
    http://www.habcycles.com
    Home of the $795 ti frame


    Report
  8. Jeff Starr
    Archived post
    #8
    JS said:

    Nope sorry, but that's not what is being depicted in their diagram. The
    part that is misleading is the vertical line that is being projected from
    the seat tube. It needs to follow the same angle as the seat tube, not
    vertically. Simple geometry dictates that the line will be be shorter than
    the sloping line below it.


    Have you tried contacting Felt?

    Are you considering the purchase of this frame?

    Life is Good!
    Jeff

    Report
  9. Jeff Starr
    Archived post
    #9
    JS said:

    Nope sorry, but that's not what is being depicted in their diagram. The
    part that is misleading is the vertical line that is being projected from
    the seat tube. It needs to follow the same angle as the seat tube, not
    vertically. Simple geometry dictates that the line will be be shorter than
    the sloping line below it.


    Have you tried contacting Felt?

    Are you considering the purchase of this frame?

    Life is Good!
    Jeff

    Report

Keep exploring

Browse the sectionCycling Equipment Return to CyclingForumsStart at the home page Search discussionsFind another thread

Active in the last 60 minutes

Active in this thread

0 users · 0 guests ·0 bots ·0 total

No signed-in users are active right now.

No known search crawlers active right now.