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 08-03-08, 04:48 PM   #1
Briareos
Senior Member
Thread Starter
 
Briareos's Avatar
 
Join Date: Oct 2006
Location: Illinois
Bikes: No bike at the moment; In process of building it.
Posts: 539
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Question Regarding the Design of Ti Frames

From what I've read, Ti's advantages are:longevity, nice ride, strong and some others I can't remember.

But what I read it suffers from, is that it isn't as stiff as alu or carbon.

My question is...Would a "Triple-Triangle" layout for a Ti frame increase the stiffness enough to make it worth building that way? Maybe add a small triangle wedge between the seat-tube and the down-tube at the bottom...
Briareos is offline   Reply With Quote
Old 08-03-08, 07:21 PM   #2
Nessism
Senior Member
 
Nessism's Avatar
 
Join Date: Jun 2004
Location: Torrance, CA
Bikes: Homebuilt steel
Posts: 2,333
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
The stiffness of a tube is controlled by two factors: the metal stiffness, characterized by the Modulus of Elasticity or Young's Modulus, and a shape factor known as the Area Moment of Inertia.

Ti as a metal is not as stiff as steel (Young's modulus is lower), but stiffer than aluminum. As you know, most aluminum frames are bone rattling stiff. Why? because the shape factor, Moment of Inertia, is high (large diameter tubes and fairly thick)- Aluminum as a material is prone to cracking so the designers make the frame stiff so it doesn't flex which leads to aluminum frame failure.

So going back to your Ti frame, it's easy to build a stiff Ti frame by increasing the tubing diameters and tube thickness since this increases the shape factor. Look for a frame with a 1-1/2" diameter down tube and 1-3/8" seat tube, this frame will be nice and stiff. No need to monkey with triple triangle mumbo jumbo - just up the tube diameters. Very simple.
__________________
Becareful buying/selling bike parts on-line. I learned the hard way. :(

Good/Bad Trader Listing
Nessism is offline   Reply With Quote
Old 08-04-08, 02:42 AM   #3
Thylacine
Industry Maven
 
Thylacine's Avatar
 
Join Date: Oct 2003
Location: Wherever good bikes are sold
Bikes: Thylacines...only Thylacines.
Posts: 2,936
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Nessism View Post
Th
So going back to your Ti frame, it's easy to build a stiff Ti frame by increasing the tubing diameters and tube thickness since this increases the shape factor..... Very simple.
There's your answer right there.
Thylacine is offline   Reply With Quote
Old 08-04-08, 10:58 AM   #4
NoReg
Banned
 
Join Date: Aug 2005
Bikes:
Posts: 5,117
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
" tubing diameters and tube thickness since this increases the shape factor..... Very simple."

Isn't that just increasing dimensions, how is that a shape factor? Changing wall thickness as a ratio, or changing from round to square is one thing, but just using bigger tubes just sounds like a dimensional change. Often when tubing diameter is increased in bikes the material used retains the same wall thickness so the dimension increases, but the ratio of wall to diameter decreases which is an inverse change in shape. Still stiffer overall because the stiffness increases to the cube of the dimensional increase.

I have no idea about the specialty terminology, however.
NoReg is offline   Reply With Quote
Old 08-04-08, 04:15 PM   #5
Nessism
Senior Member
 
Nessism's Avatar
 
Join Date: Jun 2004
Location: Torrance, CA
Bikes: Homebuilt steel
Posts: 2,333
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by Peterpan1 View Post
" tubing diameters and tube thickness since this increases the shape factor..... Very simple."

Isn't that just increasing dimensions, how is that a shape factor? Changing wall thickness as a ratio, or changing from round to square is one thing, but just using bigger tubes just sounds like a dimensional change. Often when tubing diameter is increased in bikes the material used retains the same wall thickness so the dimension increases, but the ratio of wall to diameter decreases which is an inverse change in shape. Still stiffer overall because the stiffness increases to the cube of the dimensional increase.

I have no idea about the specialty terminology, however.
The Area Moment of Inertia (shape factor) increases when the tube thickness increases remember when Columbus used to make SL/SLX for the lightweight guys and SP/SPX (which was thicker and stiffer) for the heavyweights?

Adding thickness is a viable technique to increase stiffness but increasing diameter is a better method if one is attempting to maximize stiffness to weight ratio since the Moment of Inertia increases exponentially as the material moves away from the bending axis (diameter increases).
__________________
Becareful buying/selling bike parts on-line. I learned the hard way. :(

Good/Bad Trader Listing
Nessism is offline   Reply With Quote
Old 08-05-08, 05:17 PM   #6
G0balistik
Senior Member
 
Join Date: May 2006
Location: Boston
Bikes:
Posts: 299
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
also, thicker chainstays helps.
G0balistik 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 11:42 AM.