Carbon fiber has been glorified to the point of becoming the
material of choice for anything associated with performance. The automotive
industry is perhaps to blame for that, going as far as using this relatively
exotic material in elements of interior trim for aesthetic purposes. But does
carbon fiber live up to the hype, and is it better than all of its metal
alternatives? Better is always relative, but carbon fiber earned its place in
the bike frame world quite fairly.
To even be considered a material of choice, it must perform well in the most important measure of a bike-frame’s quality – the strength-to-weight ratio. And it does. It outperforms aluminium in all cases, and in most cases gives titanium a run for its money. But there are also unique advantages where it has no rivals. If I were to ask you to draw a bike frame, I can easily predict the approximate shape you are going to draw. But bike frame engineering has gone quite far in designing and engineering elaborate shapes that, if possible to manufacture, would offer exceptional benefits. As we have discussed, with metals, the more you chase the ultimate strength-to-weight ratio material, the more difficult that material becomes to work with. This means that a titanium frame, for example, will never be of a particularly complex shape. It will be approximately the shape you would have drawn. This is where carbon fiber blows its metal rivals out of the water. Carbon fiber can be used to create virtually any shape, with an endless variety of thickness, density or angles. That means an exotically shaped bike frame that wants to house an innovative suspension system will most likely be made of carbon fiber.
To have that level of control over the frame’s dimensions and shape means you can tune the frame itself to the exact use case of the bike. For example, if you’re designing the bike to go over rough terrain, you can engineer the carbon fiber frame to be just flexible enough at key sections in the frame for it to absorb the shock without additional damping elements.
All this is made possible by the unique manufacturing process of carbon fiber. Carbon fiber in its raw form is a material that looks a little like textile. It is woven into thicker bundles and, most commonly, put together as a sheet of weaves held together by a special resin. If you want a specific shape, what you need to do is design a mold of that shape. Carbon fiber sheets are layered on top of each other until the desired thickness is achieved. Once layered, the mold is the pressurised and placed in an oven to bake. This is a simplistic overview of the process, but the reality is naturally more complex. One of the reasons why carbon frames are expensive is that the layering of the material has to be done by hand, which makes mass production of frames highly labor intensive. And the more complex the frame, the longer it takes. That’s why carbon fiber frames are the most expensive out there.