I was on Wiki reading about Carbon Fiber Reinforced Plastic and the article said:

Carbon fiber reinforced plastic has found lot of use in high-end sports equipment such as racing bicycles. For the same strength, a carbon-fiber frame weighs less than a bicycle tubing of aluminum or steel. The choice of weave can be carefully selected to maximize stiffness. The variety of shapes it can be built into has further increased stiffness and also allowed aerodynamic considerations into tube profiles. Carbon fiber reinforced plastic frames, forks, handlebars, seatposts and crank arms are becoming more common on medium- and higher-priced bicycles. Carbon fiber reinforced plastic forks are used on most new racing bicycles. Despite carbon fiber reinforced plastic's advantages, it has been known to fail suddenly in bicycles, causing devastating crashes.

So, my question is, we've been told how marvelous CF frames are, but in reality, are these expensive bikes really made of plastic? I understand that the CF is applied in layers and cured and becomes very strong, but the frame is fundamentally plastic, right?

It's a composite; a mixture of carbon fibers and epoxy resin (typically.) Sure, epoxy is a plastic, but saying that carbon fiber is therefore "fundamentally plastic" is misleading. If you built a frame out of pure epoxy, I doubt it would support your body weight. If you built a frame out of pure carbon fiber fabric, I know it wouldn't support your bodyweight. Together, they form CFRP.

But does it really matter if it's "plastic?" Seems like semantics to me. Is your CFRP bike suddenly less luxe because it's "plastic?"

Not exactly. Not anymore than Fiberglas® glass-reinforced matrix is plastic. Carbon fiber laminate is a form of cloth impregnated with liquid polymer--plastic--layered, molded, and cured. You could say the frame was fundamentally fabric.

Why not just say it is fundamentally made of cloth?

Because that is misleading, just like saying carbon bikes are "plastic". It's the combination of carbon fiber cloth and resin binders that give the final product its characteristics. Calling them either cloth or plastic is like calling aluminum frames "beer cans" or steel frames "tin cans".

OK, thanks guys, I was under the impression that bike makers started with a complete frame, but made of plastic, then they wrapped the plastic frame with CF fabric. I thought maybe they needed the plastic sub frame to get those cool shapes and angles.

OK, now I get it.

Did you also know that steel comes from iron ore, so it is really just a rock? Just like the bikes that Fred Flintstone rode?

jim

The new Belgian Museeuw carbon frames incorporate a great deal of flax in their construction - also in the deep rims they make. I haven't seen one, let alone ridden one but the review was very positive - seems it gives a softer ride without losing stiffness and lightness. A bike made of CLOTH!!!

That's not technically correct. Most carbon fiber is made from polyacrylonitrile (PAN) fiber that is heated in an oxygen-free atmosphere to pyrolyze the fiber down to the carbon "backbone".

The "flax" frames you referenced are made by taking flax (aka linen) fibers and pyrolyzing them similarly. The end result is a carbon fiber nearly identical the the more common type. You do not wind up with a "cloth" bike any more than the usual carbon fiber frame is cloth.

This is a marketing gimmick to make you think the bike frame is "greener" than normal carbon construction. It isn't. If it gives a softer ride, it's in the layup and weave design, not in the material characteristics.

Thanks Hillrider, an excellent, clear explanation that even I can follow! I thought it was a bit strange because if you could build a decent frame from simply laminating and baking linen fabric, some of us would be riding modified monocoque table cloths with napkin fork blades and be quite a bit richer! Seriously though, If I understand you correctly the flax is made into a material similar to the normal carbon so it's not really a lot different. I guess I was hoping for some sort of clarification when I posted the item and once again, Bike Forum came up with the goods! Much obliged.

There's a good chance that linen in an epoxy matrix would be a decent composite. Bamboo fiber, for instance, can be made into a quality composite, even if it isn't optimal for a bike frame.

Fiber in a polymer matrix is an extraordinary technology. Carbon fiber is an extraordinary fiber, but there are many other fibers to choose from. And indeed, we may have to choose new fibers as our Perpetual War Strategy™ seems to be using up all the CF available.



™"Perpetual War" is a trademark of the Mao corporation, used with permission by the Bush administration.

My dad was a life long chemical engineer and many of the plants he helped design made plastic. He referred to reinforced plastics as "FRPs" - Fiber Reinforced Plastic.

It's like concrete. Reasonably strong on its own, but much, much stronger when it has something running through it. In concrete's case, rebar. In plastic's case, thread of some kind. Glass thread (fiberglass) is cheap, reasonably strong, but not very, very strong. Carbon fiber is stronger.

Virtually any material will work, as long as it meets certain design criteria. Some fiberglass car bodies use balsa wood as stiffners - after experimenting with a lot of different materials, balsa wood was found to be the best combination of light weight, high rigidity, and low cost.

Nothing wrong with calling it an FRP. It's just more sexy when you call it carbon fiber.

cdr