Operation Manual

72 73
PART II
2. UNDERSTANDING
COMPOSITES
(CARBON FIBER)
All riders must understand a fundamental reality
of composites. Composite materials constructed of
carbon bers are strong and light, but when crashed
or overloaded, carbon bers do not bend, they break.
What Are Composites?
The term “composites” refers to the fact that a part
or parts are made up of dierent components or
materials. You’ve heard the term “carbon ber bike.”
This really means “composite bike.”
Carbon ber composites are typically a strong, light
ber 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 ber composite
at 1.45 grams/cm3.
The composites with the best strength-to-weight ratios
are made of carbon ber in a matrix of epoxy plastic.
The epoxy matrix bonds the carbon bers together,
transfers load to other bers, and provides a smooth
outer surface. The carbon bers 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 bers
can be placed in specic orientations to optimize the
structure for particular loads. The choice of where to
place the carbon bers gives engineers a powerful tool
to create strong, light bicycles. Engineers may also
orient bers to suit other goals such as comfort and
vibration damping.
Carbon ber composites are very corrosion resistant,
much more so than most metals. Think about carbon
ber or berglass boats.
Carbon ber materials have a very high strength-to-
wieght ratio.
What Are The Limits Of
Composites?
Well designed “composite” or carbon ber bicycles
and components have long fatigue lives, usually better
than their metal equivalents.
While fatigue life is an advantage of carbon ber, GT
still urges you to regularly inspect your carbon ber
frame, fork, or components.
Carbon ber 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 may be delamination of carbon ber
or carbon ber 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, fallen cyclist
or other object. First, read the Important warnings at
the beginning of PART II Section A. Bicycles Cannot
Protect You in this manual.
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 and
fork 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. See Figure A on page 68. Note the
signicant dierence in behavior between carbon and
metal. 1. Understanding Metals in this section. 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.
Our carbon frames/fork/components are designed
for normal riding loads with a factor of safety. These
frames/fork/components will be broken by some crash
or impact loads.
See “Composite Frame, Fork, And Component
Inspection” on next page.