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Why Are Composites Used?
Unlike metals, which have uniform properties in all directions (engineers call this isotropic), carbon fibers can
be placed in specific orientations to optimize the structure for particular loads. The choice of where to place
the carbon fibers gives engineers a powerful tool to create strong, light bicycles. Engineers may also orient
fibers to suit other goals such as comfort and vibration damping.
Carbon fiber composites are very corrosion resistant, much more so than most metals. Think about carbon
fiber or fiberglass boats.
Carbon fiber materials have a very high strength-to-weight ratio.
What Are The Limits Of Composites?
Well designed “composite” or carbon fiber bicycles and components have long fatigue lives, usually better
than their metal equivalents.
While fatigue life is an advantage of carbon fiber, you must still regularly inspect your carbon fiber frame,
fork, or components.
Carbon fiber composites are not ductile. Once a carbon structure is overloaded, it will not bend; it will
break. At and near the break, there will be rough, sharp edges and maybe delamination of carbon fiber or
carbon fiber fabric layers. There will be no bending, buckling, or stretching.
If You Hit Something Or Have A Crash, What Can You Expect From Your Carbon Fiber Bike?
Let’s say you hit a curb, ditch, rock, car, other cyclist or other object. At any speed above a fast walk, your
body will continue to move forward, the momentum carrying you over the front of the bike. You cannot and
will not stay on the bike and what happens to the frame fork and other components is irrelevant to what
happens to your body.
What should you expect from your carbon frame? It depends on many complex factors, which is why we tell
you that crash worthiness cannot be a design criteria. With that important note, we can tell you that if the
impact is hard enough, the fork or frame may be completely broken. Note the significant difference in
behavior between carbon and metal. See Section 2. A, Understanding metals in this Appendix. Even if the
carbon frame was twice as strong as a metal frame, once the carbon frame is overloaded it will not bend, it
will break completely.
WARNING:
Never use clamping devices on the tubes of carbon frames. This can cause serious damage to
the carbon frame.
WARNING:
Never use clamps on carbon frames. Clamps such as those found on bicycle work stands and car
racks can damage the carbon frame.
Inspection of Composite Frame, Fork, and Components Cracks:
Inspect for cracks, broken, or splintered areas. Any crack is serious. Do not ride any bicycle or component
that has a crack of any size.