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#1
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Frame dimensions misleading
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 |
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#2
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Frame dimensions misleading
JS wrote:
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. 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_bike...ine_bikes.html -Vee |
#3
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Frame dimensions misleading
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" wrote in message oups.com... JS wrote: 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. 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_bike...ine_bikes.html -Vee |
#4
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Frame dimensions misleading
"JS" wrote:
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 |
#5
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Frame dimensions misleading
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" wrote in message ... "JS" wrote: 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 |
#6
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Frame dimensions misleading
"JS" wrote:
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 "Mark Hickey" wrote in message .. . "JS" wrote: 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 |
#7
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Frame dimensions misleading
On Thu, 28 Jul 2005 06:09:42 GMT, "JS" wrote:
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 |
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