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One can design a part that is so strong that fatigue life is nearly infinite. This requires a lot of
material and a lot of weight. Any structure that must be light and strong will have a finite
fatigue life. Aircraft, race cars, motorcycles all have parts with finite fatigue lives. If you wanted
a bicycle with an infinite fatigue life, it would weigh far more than any bicycle sold today. So we
all make a tradeo: the wonderful, lightweight performance we want requires that we inspect
the structure.
What to look for
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.
• ONCE A CRACKS STARTS IT CAN GROW AND GROW
FAST. Think about the crack as forming a pathway to fail-
ure. This means that any crack is potentially dangerous
and will only become more dangerous.
SIMPLE RULE 1 : If you find
crack, replace the part.
• CORROSSION SPEEDS DAMAGE. Cracks grow more
quickly when they are in a corrosive environment. Think
about the corrosive solution as further weakening and
extending the crack.
SIMPLE RULE 2 : Clean your
bike, lubricate your bike, pro-
tect your bike from salt, remove
any salt as soon as you can.
• STAINS AND DISCOLORATION CAN OCCUR NEAR A
CRACK. Such staining may be a warning sign that a crack
exists.
SIMPLE RULE 3 : Inspect and
investigate any staining to see if
it is associated with a crack.
• 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 risers,” 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 frequent attention
to this area or replace the part.
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