Originally Posted by
bcpriess
1) It is arguable that carbon fiber frames are plastic. They certainly are in the sense that fiberglass body panels are - thermoset resin over layers of chop or fiber. But they have to be hand fabbed, which is expensive and time consuming. The also have the limitation of being one-sided in that the finished exterior surface will be dimension but the interior won't.
2) Injection molded thermoplastics often have limited stiffness, and in order to achieve real stiffness, must be "filled" with some sort of fiber (often glass fibers) to achieve truly rigid parts. Plus you get a 2 sided part with intentional features on both sides.
I know Lemond has been in partnership with several entities on a next gen carbon fiber technology. If I were betting on what it is, I'd think they're close to commercializing an injection molding process for carbon fiber components, which would make a molded plastic bike both a reality, and just as light/strong as existing CF frames, with a potentially lower cost.
CF composites are long fibers in a plastic matrix. But that process always involves a "lay up" because you can't "inject" fibers into a mold and expect them to orient correctly to greatly change the structural rigidity. Mainly what you get by adding short fibers to injected thermoplastics is increased shear strength rather than greatly increased stiffness. It will still act like nylon, just not break when pushed past its elastic modulus as easily.
The reason CF is strong is not because of the plastic, but the fibers. The plastic resin keeps the fibers oriented and provides some shock absorbency, but the plastic part is barely structural. The resin is more like hard candy than aluminum.
I think you could make a decent bike out of good fiber and fairly "weak" resin, but you'd have an awful hard time making a decent bike out of great plastic and poor fibers.