Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 06-18-08, 05:43 PM   #1
1jacktripper
Senior Member
Thread Starter
 
1jacktripper's Avatar
 
Join Date: Jan 2007
Bikes:
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Geometry conversion from compact sloping frame

Hi everyone,

Not sure if I'm in the right forum. If not, I apologize, and I'd appreciate directing me to the right forum.

I am wondering about the following: if a compact sloping frame has a 42cm seat-tube length, I imagine it does not automatically mean I'll need a 42cm size regular frame, correct? By "regular", I meant non-sloping traditional horizontal frame.

Follow-on question: how do I, if it's possible, convert the measurements of such a compact sloping frame into a regular frame? That is, can the geometry of a compact sloping frame tell me what geometry I'd need in a regular traditional horizontal frame in order to achieve similar fit?

Thanks very much!

Jack
1jacktripper is offline   Reply With Quote
Old 06-18-08, 07:10 PM   #2
Scooper
Decrepit Member
 
Scooper's Avatar
 
Join Date: Aug 2005
Location: San Francisco California
Bikes: Waterford 953 RS-22
Posts: 10,137
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 38 Post(s)
Giant has a brief treatise on relating bikes with compact geometry to bikes with traditional geometry HERE.

The Giant TCR Advanced Team compact geometry is HERE.

Hope this helps.
__________________
- Stan
I'm with her.
Scooper is online now   Reply With Quote
Old 06-18-08, 09:18 PM   #3
Live Wire 
Framebuilder
 
Join Date: Dec 2007
Bikes:
Posts: 530
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Seat tube length and top tube slope are incidental products of a design aesthetic and/or the need for standover clearance- they don't have an effect on the geometry (ht/st angles, etc) of the frame at all.
To compare your compact Giant (ugh) with a traditional looking road frame (bonus ) measure horizontally from the top of the stem to the seatpost.
happy bike hunting!

Last edited by Live Wire; 06-18-08 at 09:38 PM.
Live Wire is offline   Reply With Quote
Old 06-18-08, 10:34 PM   #4
1jacktripper
Senior Member
Thread Starter
 
1jacktripper's Avatar
 
Join Date: Jan 2007
Bikes:
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Scooper View Post
Giant has a brief treatise on relating bikes with compact geometry to bikes with traditional geometry HERE.

The Giant TCR Advanced Team compact geometry is HERE.

Hope this helps.

Thanks, Stan. This is very helpful!
1jacktripper is offline   Reply With Quote
Old 06-18-08, 10:40 PM   #5
1jacktripper
Senior Member
Thread Starter
 
1jacktripper's Avatar
 
Join Date: Jan 2007
Bikes:
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Live Wire View Post
Seat tube length and top tube slope are incidental products of a design aesthetic and/or the need for standover clearance- they don't have an effect on the geometry (ht/st angles, etc) of the frame at all.
To compare your compact Giant (ugh) with a traditional looking road frame (bonus ) measure horizontally from the top of the stem to the seatpost.
happy bike hunting!
Thanks, Chauncey! I mentioned the seat tube length because I have a shorter-than-the-average-Joe legs. But from what you are saying, it sounds like I just need to measure from top of the stem to the [top or junction of?] seatpost?

Great website, by the way!
1jacktripper is offline   Reply With Quote
Old 06-19-08, 09:25 PM   #6
Live Wire 
Framebuilder
 
Join Date: Dec 2007
Bikes:
Posts: 530
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by 1jacktripper View Post
Thanks, Chauncey! I mentioned the seat tube length because I have a shorter-than-the-average-Joe legs. But from what you are saying, it sounds like I just need to measure from top of the stem to the [top or junction of?] seatpost?

Great website, by the way!
Jack,
Thanks.
Yes, measure from the top of the stem(the bolt that goes in the steerer) to the center of the seatpost while holding the tape horizontally. This will give you the "effective" top tube measurement regardless of the tt slope. This is also the way most manufacturers measure tt length and the main measurement a custom builder uses to tailor a frame to fit.
Live Wire is offline   Reply With Quote
Old 07-02-08, 10:21 AM   #7
1jacktripper
Senior Member
Thread Starter
 
1jacktripper's Avatar
 
Join Date: Jan 2007
Bikes:
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Hi,

Not sure if this is going to come out right, but I'd greatly appreciate any help. Also, I am wondering if I'm posting on the wrong sub-forum here, so much apologies if that is the case.

I currently have a compact frame with the measurements as attached, and it fits me really well, but I am wondering if such measurements would translate to the 49cm measurement (for traditional/horizontal toptube geometry) in the second page of the attachment.

If not the 49cm, maybe the 50cm?

Or is it not as easy as I'm making it out to be?

Thanks much!

Current frame geometry:



New frame geometry:


Last edited by 1jacktripper; 07-02-08 at 01:15 PM. Reason: Adding Image files
1jacktripper is offline   Reply With Quote
Old 07-02-08, 12:24 PM   #8
Scooper
Decrepit Member
 
Scooper's Avatar
 
Join Date: Aug 2005
Location: San Francisco California
Bikes: Waterford 953 RS-22
Posts: 10,137
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 38 Post(s)
Quote:
Originally Posted by 1jacktripper View Post
Hi,

Not sure if this is going to come out right, but I'd greatly appreciate any help. Also, I am wondering if I'm posting on the wrong sub-forum here, so much apologies if that is the case.

I currently have a compact frame with the measurements as attached, and it fits me really well, but I am wondering if such measurements would translate to the 49cm measurement (for traditional/horizontal toptube geometry) in the second page of the attachment.

If not the 49cm, maybe the 50cm?

Or is it not as easy as I'm making it out to be?

Thanks much!
Maybe this will help.

For the drawing on page 1 of your attachment, it appears the manufacturer is using the intersection of the top tube and the head tube (instead of the top of the handlebar stem) as the datum for determining the location to measure horizontally to the extended seat tube centerline to derive the virtual frame size.

I've marked up your drawing, and using a Gerber Variable Scale, measured what would be the center-to-center dimension of the seat tube (from the center of the bottom bracket shell to the intersection of the center of the virtual horizontal top tube and the center of a virtual extended seat tube. That dimension is 51.8cm.

If you used the top of the handlebar stem as the datum, the intersection of a virtual horizontal top tube with the centerline of an extended virtual seat tube would be 60cm.

If you look at the drawing, you'll see that this manufacturer drew the virtual top tube c-to-c measurement as 534mm, or 53.4cm, and that he used the head tube/top tube intersection for the datum.

__________________
- Stan
I'm with her.
Scooper is online now   Reply With Quote
Old 07-02-08, 01:20 PM   #9
1jacktripper
Senior Member
Thread Starter
 
1jacktripper's Avatar
 
Join Date: Jan 2007
Bikes:
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Scooper View Post
Maybe this will help.
...

I've marked up your drawing, and using a Gerber Variable Scale, measured what would be the center-to-center dimension of the seat tube (from the center of the bottom bracket shell to the intersection of the center of the virtual horizontal top tube and the center of a virtual extended seat tube. That dimension is 51.8cm.

If you used the top of the handlebar stem as the datum, the intersection of a virtual horizontal top tube with the centerline of an extended virtual seat tube would be 60cm.

...
Stan,

Thanks much! If I am understanding you, it sounds like you are saying that I should be looking for a farme size with a seat tube measurement of 51.8 cm and top tube 60 cm? Hmm...if that is the case, then I guess none of the options in the new frame geometry would be appropriate then. Bummer...
1jacktripper is offline   Reply With Quote
Old 07-02-08, 02:04 PM   #10
Scooper
Decrepit Member
 
Scooper's Avatar
 
Join Date: Aug 2005
Location: San Francisco California
Bikes: Waterford 953 RS-22
Posts: 10,137
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 38 Post(s)
Quote:
Originally Posted by 1jacktripper View Post
Stan,

Thanks much! If I am understanding you, it sounds like you are saying that I should be looking for a farme size with a seat tube measurement of 51.8 cm and top tube 60 cm? Hmm...if that is the case, then I guess none of the options in the new frame geometry would be appropriate then. Bummer...
No, no... Sorry, I guess I wasn't clear enough. You should be looking for a frame with a 51.8cm (or 52cm) seat tube measured center-to-center, and with a top tube of 53.4cm center-to-center.

Disregard the 60cm dimension; that was just to show you what the c-c seat tube would be if you measured horizontally from the top of the stem instead of from the top tube/head tube junction. It just confuses the issue.
__________________
- Stan
I'm with her.
Scooper is online now   Reply With Quote
Old 07-02-08, 02:38 PM   #11
1jacktripper
Senior Member
Thread Starter
 
1jacktripper's Avatar
 
Join Date: Jan 2007
Bikes:
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Scooper View Post
No, no... Sorry, I guess I wasn't clear enough. You should be looking for a frame with a 51.8cm (or 52cm) seat tube measured center-to-center, and with a top tube of 53.4cm center-to-center.

Disregard the 60cm dimension; that was just to show you what the c-c seat tube would be if you measured horizontally from the top of the stem instead of from the top tube/head tube junction. It just confuses the issue.
Got it! Thanks, Stan. That's too bad, then...I saw this nice 49 cm frame on CL. Oh well, at least now I know the more exact spec's. Off to shopping I go!
1jacktripper is offline   Reply With Quote
Old 07-30-08, 10:35 AM   #12
1jacktripper
Senior Member
Thread Starter
 
1jacktripper's Avatar
 
Join Date: Jan 2007
Bikes:
Posts: 787
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
[Bump]

I've recently inherited a frame, and I'm wondering if you wouldn't mind sharing with me your thoughts as to whether if my conclusion that the geometry is close enough to what was suggested in this thread.

The new frame I found has the following geometry center-to-center:
top tube: 21.5 inches, or 54.6 cm
seat tube: 20 inches, or 50.8 cm
bottom tube: 24 inches, or 61 cm
head tube (tip to tip): 3.5 inches, or 8.9 cm

The suggestion in this thread so far was to find a top tube with length of 53.4 cm and seat tube of 52. I figure if I play a bit with the stem, bar (perhaps a moustache bar), and seat post length, I can make this new frame work. I'm thinking of converting this new frame into a fixie/townie/commuter (max 15-mile ride), so perhaps the frame doesn't have to be at very dialed-in fit.

What do you think? Thanks very much!
1jacktripper is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 08:50 AM.