Notices
General Cycling Discussion Have a cycling related question or comment that doesn't fit in one of the other specialty forums? Drop on in and post in here! When possible, please select the forum above that most fits your post!

Top tube question

Old 03-20-12, 11:33 AM
  #1  
Senior Member
Thread Starter
 
zenith's Avatar
 
Join Date: Mar 2012
Location: Alberta, Canada
Posts: 207

Bikes: 91 Bianchi squadra, 94 CCM black ice, 02 eclipse hybrid, 88 Fiori Piquante, 2013 Deddaccai, 1930's Humber and many more

Likes: 0
Liked 0 Times in 0 Posts
Top tube question

I have been wondering why (in ten speeds / road bikes) the top tube length doesn't vary or very little. Seems like the builders only make the frame taller by elongating the head tube, the seat tube and the rear stay but the top remain the same. Is there a reason behind that? What I understand out of this is that you could also just raise the head set and the saddle and you'd be set to go. The only difference would be a lower top tube to your bike.
Then, while I was shopping for a 09 Marin Portofino I noticed that the new bike do have a bigger difference in the top tube then the older bikes.
I'm confused!
zenith is offline  
Old 03-20-12, 11:41 AM
  #2  
Administrator
 
Join Date: Feb 2005
Location: Delaware shore
Posts: 13,565

Bikes: Cervelo C5, Guru Photon, Waterford, Specialized CX

Liked 2,250 Times in 1,510 Posts
Most raod bikes have "sqaure" design - the top tube length and seat tube are the same. For example a 56cm bike with that seat tube has a 56cm top tube. Caution - with sloping top tubes, you need to use the effective seat tube length (the spot of the seat tube where the top tube makes contact if it were horizontal).

But top tubes get longer with larger size frames
StanSeven is offline  
Old 03-20-12, 12:17 PM
  #3  
Senior Member
 
Join Date: Sep 2007
Location: Far beyond the pale horizon.
Posts: 14,458
Liked 1,454 Times in 1,009 Posts
Originally Posted by zenith
I have been wondering why (in ten speeds / road bikes) the top tube length doesn't vary or very little. Seems like the builders only make the frame taller by elongating the head tube, the seat tube and the rear stay but the top remain the same. Is there a reason behind that? What I understand out of this is that you could also just raise the head set and the saddle and you'd be set to go. The only difference would be a lower top tube to your bike.
Then, while I was shopping for a 09 Marin Portofino I noticed that the new bike do have a bigger difference in the top tube then the older bikes.
I'm confused!
It doesn't work the way you think it does.

The size of the bike (54 cm, for example) is typically the length of the seat tube (a few manufacturers use the horizontal top tube length to indicate size).

As the seat tube length changes, so, generally, do the other frame dimensions (but not necessarily proportionally).

Looking at the the geometry chart for a particular model shows that clearly.

For example:

https://www.cervelo.com/en_us/bikes/2012/rs/geometry/

Note that funny things can happen at small sizes (sometimes, with extra large sizes too).

Last edited by njkayaker; 03-20-12 at 12:21 PM.
njkayaker is online now  
Old 03-20-12, 12:25 PM
  #4  
Banned.
 
Mr. Beanz's Avatar
 
Join Date: Dec 2005
Location: Upland Ca
Posts: 19,895

Bikes: Lemond Chambery/Cannondale R-900/Trek 8000 MTB/Burley Duet tandem

Likes: 0
Liked 4 Times in 3 Posts
Originally Posted by zenith
the top tube length doesn't vary or very little. ..............I'm confused!
Yes, I believe you are confused. I have a 52 cm bike and a 58. There is a 2 inch difference in the top tube length and a 1 1/2 difference in the set tube length.

There is actually a bigger difference in the top tube length compared to the seat tube length.

A taller bike with a 2 inch difference in length from the shorter frame is a pretty big difference to me.
Mr. Beanz is offline  
Old 03-20-12, 12:40 PM
  #5  
Banned
 
Join Date: May 2009
Posts: 2,078
Likes: 0
Liked 4 Times in 4 Posts
It does vary. You may be going by cheap tenspeeds from the 70s and 80s. It was that way but isn't anymore. If you look at the specifications of any modern bike except the cheapest ones, there is a table of tube lengths and it shows the top tube length varies.
garage sale GT is offline  
Old 03-20-12, 12:55 PM
  #6  
Senior Member
Thread Starter
 
zenith's Avatar
 
Join Date: Mar 2012
Location: Alberta, Canada
Posts: 207

Bikes: 91 Bianchi squadra, 94 CCM black ice, 02 eclipse hybrid, 88 Fiori Piquante, 2013 Deddaccai, 1930's Humber and many more

Likes: 0
Liked 0 Times in 0 Posts
I was referring to 10 speeds from 70's mostly. I know that the newer bikes are not that way. What was the purpose of just making the older "cheap" bikes just taller?
zenith is offline  
Old 03-20-12, 03:10 PM
  #7  
Banned
 
Join Date: May 2009
Posts: 2,078
Likes: 0
Liked 4 Times in 4 Posts
They probably wanted to cut down the total number of parts they had to stock. You would need different head tube and bottom bracket lugs in order to accomodate different frame angles, as well as different top and down tubes. It's one of the things that can sap the economy out of high speed, high volume production.
garage sale GT is offline  
Old 03-20-12, 04:31 PM
  #8  
Banned
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 43,598

Bikes: 8

Liked 1,360 Times in 866 Posts
I have 2 bikes that are both red.. 1 is a 56, 55.5 Top tube, the other is a 57x57,
some variation by different frame makers [japan red or italian red in this case]

or the contract details for the same company that makes parts for different importers
under their individual brand names .
fietsbob is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
antontoni
Framebuilders
8
10-24-17 05:32 AM
dyprious
Fitting Your Bike
6
10-31-16 12:16 PM
Regulatori
Singlespeed & Fixed Gear
3
02-20-16 01:00 PM
Carson Dyle
Fitting Your Bike
5
12-09-14 12:28 PM
damnable
Road Cycling
3
06-09-11 05:33 AM

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Your Privacy Choices -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.