Jamis Bicycle Owner's Manual - page 29
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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
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.
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 tradeoff: the wonderful, lightweight
performance we want requires that we inspect the structure.
What to look for
•ONCEACRACKSSTARTSITCANGROWANDGROW
FAST. Think about the crack as forming a pathway to failure.
This means that any crack is potentially dangerous and will
only become more dangerous.
SIMPLE RULE 1 : If you find crack,
replace the part.
•CORROSSIONSPEEDSDAMAGE.Cracksgrowmore
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, protect
your bike from salt, remove any
salt as soon as you can.
•STAINSANDDISCOLORATIONCANOCCURNEARA
CRACK.Suchstainingmaybeawarningsignthatacrack
exists.
SIMPLE RULE 3 : Inspect and
investigate any staining to see if
it is associated with a crack.
•SIGNIFICANTSCRATCHES,GOUGES,DENTSORSCOR-
INGCREATESTARTINGPOINTSFORCRACKS.Thinkabout
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.
•SOMECRACKS(particularlylargerones)MAYMAKE
CREAKINGNOISEASYOURIDE.Thinkaboutsuchanoiseas
a serious warning signal. Note that a well-maintained bicycle
will be very quiet and free of creaks and squeaks.
SIMPLE RULE 5 : Investigate and
find the source of any noise. It
may not a be a crack, but what-
ever is causing 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.”