Bedienungsanleitung Cannondale 2011 (Seite 69 von 106) (Englisch)

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PART II

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

dierent 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 Cannondale has used

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. With that important note, we can tell you

that if the impact is hard enough the fork or frame

may be bent or buckled.

See Figure A on page 68. On a most all steel bikes,

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.

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