44
45
WARNING: Do not ride a bicycle or component with any crack, bulge
or dent, even a small one. Riding a cracked frame, fork or component
could lead to complete failure, with risk of serious injury or death.
B. Understanding composites
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.
Felt Carbon Fiber Frame Care:
Many Felt bicycles feature a carbon-fiber frame.
Such frames require special care. To learn more, please refer to the special
warning card included in the box with your bicycle or visit: http://www.feltbicycles.
com.
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/cm
3
(grams per cubic centimeter), titanium 4.5 grams/cm
3
,
aluminum 2.75 grams/cm
3
. Contrast these numbers with carbon fiber composite
at 1.45 grams/cm
3
.
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.
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.
• SIGNIFICANT SCRATCHES, GOUGES, DENTS
OR SCORING CREATE STARTING POINTS FOR
CRACKS. Think about the cut surface as a focal point
for stress (in fact engineers call such areas “stress ris-
ers,” areas where the stress is increased). Perhaps you
have seen glass cut? Recall how the glass was scored
and then broke on the scored line.
SIMPLE RULE 4 : Do not
scratch, gouge or score any
surface. If you do, pay fre-
quent attention to this area or
replace the part.
• SOME CRACKS (particularly larger ones) MAY MAKE
CREAKING NOISE AS YOU RIDE. Think about such a
noise as a serious warning signal. Note that a well-
maintained bicycle will be very quiet and free of creaks
and squeaks.
SIMPLE RULE 5 : Investi-
gate and find the source of
any noise. It may not a be a
crack, but whatever is caus-
ing the noise should be fixed
promptly.
In most cases a fatigue crack is not a defect. It is a sign that the part has been
worn out, a sign the part has reached the end of its useful life. When your car
tires wear down to the point that the tread bars are contacting the road, those
tires are not defective. Those tires are worn out and the tread bar says “time for
replacement.” When a metal part shows a fatigue crack, it is worn out. The crack
says “time for replacement.”
Fatigue Is Not A Perfectly Predictable Science
Fatigue is not a perfectly predictable science, but here are some general
factors to help you and your dealer determine how often your bicycle should be
inspected. The more you fit the “shorten product life” profile, the more frequent
your need to inspect. The more you fit the “lengthen product life” profile, the less
frequent your need to inspect.
Factors that shorten product life:
Hard, harsh riding style
“Hits”, crashes, jumps, other “shots” to the bike
High mileage
Higher body weight
Stronger, more fit, more aggressive rider
Corrosive environment (wet, salt air, winter road salt, accumulated
sweat)
Presence of abrasive mud, dirt, sand, soil in riding environment
Factors that lengthen product life:
Smooth, fluid riding style
No “hits”, crashes, jumps, other “shots” to the bike
Low mileage
Lower body weight
Less aggressive rider
Non-corrosive environment (dry, salt-free air)
Clean riding environment