A Cycling & bikes forum. CycleBanter.com

Go Back   Home » CycleBanter.com forum » rec.bicycles » Techniques
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Frame dimensions misleading



 
 
Thread Tools Display Modes
  #1  
Old July 28th 05, 02:54 AM
JS
external usenet poster
 
Posts: n/a
Default 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


Ads
  #2  
Old July 28th 05, 03:09 AM
Vee
external usenet poster
 
Posts: n/a
Default 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  
Old July 28th 05, 03:15 AM
JS
external usenet poster
 
Posts: n/a
Default 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  
Old July 28th 05, 04:46 AM
Mark Hickey
external usenet poster
 
Posts: n/a
Default 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  
Old July 28th 05, 07:09 AM
JS
external usenet poster
 
Posts: n/a
Default 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  
Old July 28th 05, 02:29 PM
Mark Hickey
external usenet poster
 
Posts: n/a
Default 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  
Old July 28th 05, 02:43 PM
Jeff Starr
external usenet poster
 
Posts: n/a
Default 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
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Autofaq now on faster server Simon Brooke UK 216 April 1st 05 10:09 AM
what frame size bike for 6'4" male? Chris Tribiono Mountain Biking 21 March 20th 05 09:52 PM
FAQ Just zis Guy, you know? UK 27 September 5th 03 10:58 PM
Is my frame salvagable? john_childs Unicycling 5 August 14th 03 11:16 AM


All times are GMT +1. The time now is 01:41 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 CycleBanter.com.
The comments are property of their posters.