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 Frames & Materials Page: 2 of 4

Materials for Frames (continued)

Steel

"Steel has been around a long time. It's probably the most researched, well known, and the most used material in just about every industry. It's the most tunable, in the sense that if you want to tune a frame the way someone tunes a piano, you have a really great selection of tubes that you can select from." Steel is also generally the most affordable of the materials listed here.

Paolo S. RealMedia Clip
Paolo talks about working with steel.

Two types of tubing
A section of thin-walled steel tubing next to a thicker-walled aluminum tube. Even with the thick wall, the aluminum tube is lighter.

Aluminum

"Aluminum is an interesting material. You can't really let it flex, because the more it gets to bend the quicker it reaches the end of its life. That's why you see a lot of aluminum frames today that have very large diameter tubing. That's to limit the flexing that happens as you ride the bike."

  RealMedia Clip

Paolo discusses the qualities of aluminum.

Titanium

"It seems that titanium is the material of choice. It has a great strength-to-weight ratio. You don't need to paint it and it looks good over a long period of time. It has forgiving qualities when it collides with other things. It tends to return to its original shape," explained Paolo. The cost however is another matter. Titanium tubing can cost up to 15 times more than steel.

  RealMedia Clip

Paolo talks about titanium.

Welding
Paolo has mastered the difficult technique of welding titanium. Proper welds and the strength of the material will ensure that the final frame is strong enough to handle a variety of stresses.

titanium frame
Paolo examines a recently welded headtube on a titanium frame. Paolo welds steel, aluminum, and titanium. To create a carbon-fiber bike the torch is put away and layers of carbon "fabric" are placed over a template or in a mold.

Carbon-Fiber

"It's the boat builder's material, as a friend of mine calls it. It's really interesting because unlike the other materials, where you have to draw it into a tube or forge it into a section, with carbon you can literally change the direction of the fabric in a certain area which will affect the way a load comes through that area. So in a sense when you build a carbon frame you feel like a tailor."

  RealMedia Clip

Paolo talks about using carbon-fiber for frames.



Yield and Ultimate Strength

One way to compare materials is to look at their yield and ultimate strength. Paolo used an example of a plastic comb. "When you bend a plastic comb, you let go and it will return to its original form. Then there is a point where you bend a plastic comb and it keeps the shape you've bent it into. Then there's a point where you actually break it."

broken wheel
In this case the frame held together but the wheel failed. Although (as mentioned in "The Wheel" section) bicycle wheels are one of the strongest man-made structures, extreme forces can overcome them. Click on the image to view a QuickTime movie (880K) of what caused this.
IMAGE & VIDEO PROVIDED BY LOGAN KELSEY

These three modes for comparison of materials are quite important because they affect how a frame is designed. The most visible example of this is the large tubing one sees on aluminum bicycles. Paolo explained that the yield and ultimate strength of aluminum are quite close. This means that if the bicycle is subjected to strong forces, the point at which it will bend is very close to the point at which it would fail completely. The large size tubing is stronger than its smaller counterparts and keeps the bike from flexing or bending--since that might mean the material would fail.

 

 Frames & Materials Page: 2 of 4
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