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PART 2
2. Understanding Composites (Carbon Fiber)
Section D. Inspect For Safety
GT Bicycle Owner’s Manual
2. Understanding Composites
(Carbon Fiber)
All riders must understand a fundamental reality
of composites. Composite materials constructed
of carbon fibers are strong and light, but when
crashed or overloaded, carbon fibers do not
bend, they break.
What Are Composites?
The term “composites” refers to the fact that a
part or parts are made up of different
components or materials. You’ve heard the term
“carbon fiber bike.” This really means
“composite bike.”
Carbon fiber composites are typically a strong,
light fiber in a matrix of plastic, molded to form a
shape. Carbon composites are light relative to
metals. Steel weighs 7.8 grams/cm3 (grams per
cubic centimeter), titanium 4.5 grams/cm3,
aluminum 2.75 grams/cm3. Contrast these
numbers with carbon fiber composite at 1.45
grams/cm3.
The composites with the best strength-to-weight
ratios are made of carbon fiber in a matrix of
epoxy plastic. The epoxy matrix bonds the
carbon fibers together, transfers load to other
fibers, and provides a smooth outer surface. The
carbon fibers are the “skeleton” that carries the
load.
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.
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