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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 in 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
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/
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 failure. It is very important that you read The
basics of metal fatigue below.
Let’s 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.
It is now common for the main frame to be made of metal and the fork of carbon fiber.
See Section B, Understanding composites below. The relative ductility of metals and
the lack of ductility of carbon fiber means that in a crash scenario you can expect some
bending or bucking in the metal but none in the carbon. Below some load the carbon
Appendix B
The lifespan of your bike and its components
1. Nothing Lasts Forever, Including Your Bike.
When the useful life of your bike or its components is over, continued use is hazardous.
Every bicycle and its component parts have a finite, limited useful life. The length
of that life will vary with the construction and materials used in the frame and
components; the maintenance and care the frame and components receive over their
life; and the type and amount of use to which the frame and components are subjected.
Use in competitive events, trick riding, ramp riding, jumping, aggressive riding, riding
on severe terrain, riding in severe climates, riding with heavy loads, commercial
activities and other types of non-standard use can dramatically shorten the life of the
frame and components. Any one or a combination of these conditions may result in an
unpredictable failure.
All aspects of use being identical, lightweight bicycles and their components will
usually have a shorter life than heavier bicycles and their components. In selecting
a lightweight bicycle or components you are making a tradeoff, favoring the higher
performance that comes with lighter weight over longevity. So, If you choose
lightweight, high performance equipment, be sure to have it inspected frequently.
You should have your bicycle and its components checked periodically by your
dealer for indicators of stress and/or potential failure, including cracks, deformation,
corrosion, paint peeling, dents, and any other indicators of potential problems,
inappropriate use or abuse. These are important safety checks and very important to
help prevent accidents, bodily injury to the rider and shortened product life.
2. Perspective
Today’s high-performance bicycles require frequent and careful inspection and
service. In this Appendix we try to explain some underlying material science basics and
how they relate to your bicycle. We discuss some of the trade-offs made in designing
your bicycle and what you can expect from your bicycle; and we provide important, basic
guidelines on how to maintain and inspect it. We cannot teach you everything you need
to know to properly inspect and service your bicycle; and that is why we repeatedly urge
you to take your bicycle to your dealer for professional care and attention.
WARNING: Frequent inspection of your bike is important to your safety. Follow
the Mechanical Safety Check in Section 1.C of this Manual before every ride.
Periodic, more detailed inspection of your bicycle is important. How often this more
detailed inspection is needed depends upon you.
You, the rider/owner, have control and knowledge of how often you use your bike,
how hard you use it and where you use it. Because your dealer cannot track your use,
you must take responsibility for periodically bringing your bike to your dealer for
inspection and service. Your dealer will help you decide what frequency of inspection
and service is appropriate for how and where you use your bike.
For your safety, understanding and communication with your dealer, we urge you
to read this Appendix in its entirety. The materials used to make your bike determine
how and how frequently to inspect.
