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PART 2
1. Understanding Metals
138692 Rev 0 (04/22)
Section D. Inspect For Safety
GT Bicycle Owner’s Manual
1. Understanding Metals
Steel is the traditional material for building
bicycle frames. It has good characteristics, but in
high performance bicycles, steel has been
largely replaced by aluminum and some
titanium. The main factor driving this change is
interest by enthusiast customers 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 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. The 6000 series aluminum alloys in
use for years are commonly used in marine
applications. 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/cm3 (grams
per cubic centimeter), titanium 4.5 grams/cm3,
aluminum 2.75 grams/cm3. Contrast these
numbers with carbon fiber composite at 1.45
grams/cm3.
Metals are subject to fatigue. With enough cycles
of use, at high enough loads, metals will
eventually develop cracks that lead to breakage.
It is very important that you read Metal Fatigue
101 next.
Let’s say you hit a curb, ditch, rock, car, fallen
cyclist or other object. First, read the Important
warnings at the beginning of SECTION A:
Bicycles Cannot Protect You.
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 and fork 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 crash
worthiness cannot be a design criteria.
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