The Lifespan of Your Bicycle
& Its Components
cont’d
inspection and service is appropriate for how and where you use your bike.
For your safety and understanding, we urge you to read this section in its entirety.
The materials used to make your bike determine how frequently to inspect.
Ignoring this WARNING can lead to frame, fork or other component failure, which
can result in serious injury or death.
A. Understanding Metals
Steel is the traditional material for building bicycle frames. It has good characteristics, but
is high performance bicycles, steel has been largely replaced by aluminum and some titanium.
The main factor driving this change is interest by cycling enthusiasts in lighter bicycles.
Properties of Metals
Please understand that there is no simple statement that can be made that characterizes
the use of different metals for bicycles. What is true is how the metal is chosen is applied is much
more important than the material alone. One must look at the way the bike is designed, tested,
manufactured, supported along with the characteristics of the metal rather than seeking a
simplistic answer.
Metals vary widely in their resistance to corrosion. Steel must be protected or rust will
attack it. Aluminum and titanium quickly develop an oxide film that protects the metal from
further corrosion. Both are therefore quite resistant to corrosion. Aluminum is not perfectly
corrosion resistant, and particular care must be used where it contacts other metals and galvanic
corrosion can occur.
Metals are comparatively ductile. Ductile means bending, buckling and stretching before
breaking. Generally speaking,, of the common bicycle frame building materials steel is the most
ductile, titanium less ductile, followed by aluminum.
Metals vary in density. Density is weight per unit of material. 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
.
Metals are subject to fatigue. With enough cycles of use, at high enough loads, metals will
eventually develop cracks that lead to failure. It is important that you read The Basics Of Metal
Fatigue section of this manual.
Lets say you hit a curb, ditch, rock, car, another cyclist or other object. At any speed above
a fast walk, your body will continue to move forward, momentum carrying you over the front of the
bike. You cannot and will not stay on the bike, and what happens to the frame, fork and other
components is irrelevant to what happens to your body.
What should you expect from your metal frame? It depends on many complex factors,
which is why we tell you that crashworthiness 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 bent or buckled.
On a steel bike, the steel fork may be severely bent and the frame undamaged. Aluminum is less
ductile than steel, but you can expect the fork and frame to be bent or buckled. Hit harder and
the top tube may be broken in tension and the down tube buckled. Hit harder and the top tube
may be broken, the down tube buckled and broken, leaving the head tube and fork separated
from the main triangle.
When a metal bike crashes, you will usually see some evidence of this ductility in bent,
buckled or folded metal.
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