This is an excerpt from the owner's manual explaining metal fatigue.
7.4 The lifespan of your Gocycle and its components
WARNING! Bicycles have a limited life span for safe operation and are not indestructible.
As with all mechanical components, bicycle components are subject to wear and high stresses.
Different materials and components may react to wear, stress or fatigue in different ways. Exceeding
the useful life of your Gocycle may be hazardous.
The expected life span of a Gocycle or Gocycle component will vary with the material and
construction of the frame and components, the maintenance that is received over its life and the type
and amount of riding. Any unusual or abusive riding style, such as off-road cycling, competitive riding,
stunt cycling, jumping or riding at excessive speed and braking hard, can accelerate wear and fatigue
of components to the point where premature and sudden failure of a component may occur without
warning and risk of injury is increased.
WARNING! Regular maintenance is essential. See Section 7. Maintenance and
Adjustments in this manual and check on www.gocycle.com/safety every 3 months to see if
there are any relevant technical bulletins relating to your frame number. Failure to perform
regular checks and maintenance could result in a reduced service life of the product or render
the product unsafe to ride.
Any form of crack, scratch or change of colouring in highly stressed areas indicates that the life of the
component has been reached and you should replace it before any further use.
See the relevant Gocycle Product Manual that is available online at www.gocycle.com/safety for parts
of the Gocycle that require visual inspection from time to time.An impact to your Gocycle, either major
or minor, can cause stress and fatigue on the Gocycle and its components or compromise the
integrity of the electronics, including the battery, electronic controller, motor drive system or wiring. In
the event of an accident and if safe to do so switch the battery off.Check for visual damage before
continuing to ride the Gocycle. If the Gocycle has sustained damage other than light cosmetic
scratches such as dented, cracked, bent or misaligned components, do not ride your Gocycle until it
has been inspected by an authorised Gocycle service centre. If you are qualified to inspect your
Gocycle, consult techsupport@gocycle.com.
7.4.1 Nothing Lasts Forever, Including Your Gocycle.
When the useful life of your Gocycle or its components is over, continued use is hazardous.
Every Gocycle 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 electric bicycles and their components will usually have
a shorter life than heavier electric bicycle and their components. In selecting a lightweight electric
bicycle or components you are making a trade-off, favouring 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 Gocycle and its components checked periodically as recommended by the
Gocycle service interval by your Gocycle dealer or qualified person 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.
7.4.2 Perspective
Today’s high-performance electric 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
We discuss some of the trade-offs made in designing your Gocycle and what you can
expect from your Gocycle; 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 Gocycle;
and that is why we repeatedly urge you to take your Gocycle to your Gocycle dealer or seek
appropriate assistance from Gocycle or a qualified bicycle mechanic for professional care and
attention.
WARNING: Frequent inspection of your Gocycle is important to your safety. Follow the
Pre-Ride Checks in Section 2 of this manual before every ride.
Periodic, more detailed inspection of your Gocycle 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 Gocycle dealer or Gocycle cannot track your use, you must take
responsibility for periodically bringing your bike to your Gocycle dealer or returning it to Gocycle for
inspection and service. Your Gocycle 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 Gocycle dealer or Gocycle, we urge you
to read this Appendix in its entirety. The materials used to make your Gocycle determine how and
how frequently to inspect.
Ignoring this WARNING can lead to frame, fork or other component failure, which can
result in serious injury or death.
7.4.3 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 aluminium and some titanium and
magnesium. The main factor driving this change is interest in lighter electric bicycles by cycling
enthusiasts.
7.4.4 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.
Aluminium and Titanium and magnesium quickly develop an oxide film that protects the metal from
further corrosion. Both are therefore quite resistant to corrosion. Aluminium and magnesium are 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 Aluminium and magnesium.
Metals vary in density. Density is weight per unit of material. Steel weighs 7.8 grams/cm3 (grams per
cubic centimetre), titanium 4.5 grams/cm3, Aluminium 2.75 grams/cm3, magnesium 1.8 grams/cm3,
carbon fibre 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. Aluminium and magnesium is less ductile than
steel, but you can expect the fork and frame to be bent or buckled. Hit harder and the frame
components or wheels may be broken or buckled, leaving the head tube and fork separated from the
frame.
When a metal bike crashes, you will usually see some evidence of this ductility in bent, buckled or
folded metal.
7.4.5 The basics of metal fatigue
Common sense tells us that nothing that is used lasts forever. The more you use something, and the
harder you use it, and the worse the conditions you use it in, the shorter its life.
Fatigue is the term used to describe accumulated damage to a part caused by repeated loading. To
cause fatigue damage, the load the part receives must be great enough. A crude, often-used example
is bending a paper clip back and forth (repeated loading) until it breaks. This simple definition will help
you understand that fatigue has nothing to do with time or age.
So what kind of “damage” are we talking about? On a microscopic level, a crack forms in a highly
stressed area. As the load is repeatedly applied, the crack grows. At some point the crack becomes
visible to the naked eye. Eventually it becomes so large that the part is too weak to carry the load that
it could carry without the crack. At that point there can be a complete and immediate failure of the
part.
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 Gocycle with an infinite
fatigue life, it would weigh far more than any bicycle sold today. The wonderful, lightweight
performance we want requires that we inspect the structure.
7.4.6 What to look for
• ONCE A CRACKS STARTS IT CAN GROW AND GROW 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.
• CORROSION SPEEDS DAMAGE. Cracks grow more 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 Gocycle, protect your
Gocycle from salt, remove
any salt as soon as you can.
• SIGNIFICANT SCRATCHES, GOUGES, DENTS OR SCORING
CREATE STARTING POINTS FOR CRACKS. Think about 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.
7.4.7 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
Gocycle dealer or Gocycle determine how often your Gocycle should be inspected. The more you fitthe “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.
7.4.8 Factors that shorten product life:
• Hard, harsh riding style
• “Hits”, crashes, jumps, other “shots” to the bike
• Rough or potholed roads
• 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
7.4.9 Factors that lengthen product life:
• Smooth, fluid riding style
• No “hits”, crashes, jumps, other “shots” to the bike
• Smooth, well maintained roads
• Low mileage
• Lower body weight
• Less aggressive rider
• Non-corrosive environment (dry, salt-free air)
• Clean riding environment
WARNING: Do not ride a Gocycle or component with any crack, bulge or dent, even a
small one. Riding a cracked frame, wheel, rim, fork or component could lead to complete
failure, with risk of serious injury or death.
7.4.10 Understanding composites
All riders must understand a fundamental reality of composites. Composite materials constructed of
carbon fibres are strong and light, but when crashed or overloaded, carbon fibres do not bend, they
break.
7.4.11 What Are Composites?
The term “composites” refers to the fact that a part or parts are made up of different components or
materials. You’ve heard the term “carbon fibre bike.” This really means “composite bike.”
Carbon fibre composites are typically a strong, light fibre in a matrix of plastic, moulded to form a
shape. Carbon composites are light relative to metals. Steel weighs 7.8 grams/cm3 (grams per cubic
centimetre), titanium 4.5 grams/cm3, aluminium 2.75 grams/cm3, magnesium 1.8 grams/cm3. Contrast
these numbers with carbon fibre composite at 1.45 grams/cm3.
The composites with the best strength-to-weight ratios are made of carbon fibre in a matrix of epoxy
plastic. The epoxy matrix bonds the carbon fibres together, transfers load to other fibres, and provides
a smooth outer surface. The carbon fibres are the “skeleton” that carries the load.
7.4.12 Why Are Composites Used?
Unlike metals, which have uniform properties in all directions (engineers call this isotropic), carbon
fibres can be placed in specific orientations to optimize the structure for particular loads. The choice of
where to place the carbon fibres gives engineers a powerful tool to create strong, light bicycles.
Engineers may also orient fibres to suit other goals such as comfort and vibration damping.
Carbon fibre composites are very corrosion resistant, much more so than most metals.
Think about carbon fibre or fibreglass boats.
Carbon fibre materials have a very high strength-to-weight ratio.
7.4.13 What Are The Limits Of Composites?
Well designed “composite” or carbon fibre bicycles and components have long fatigue lives, usually
better than their metal equivalents.
While fatigue life is an advantage of carbon fibre, you must still regularly inspect your carbon fibre
frame, fork, or components.
Carbon fibre composites are not ductile. Once a carbon structure is overloaded, it will not bend; it will
break. At and near the break, there will be rough, sharp edges and maybe delamination of carbon
fibre or carbon fibre fabric layers. There will be no bending, buckling, or stretching.
7.4.14 If You Hit Something Or Have A Crash, What Can You Expect From Your Carbon
Fibre Bike?
Let’s say you hit a curb, ditch, rock, car, other cyclist or other object. At any speed above a fast walk,
your body will continue to move forward, the 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 carbon frame? It depends on many complex factors. But we can
tell you that if the impact is hard enough, the carbon fibre component may be completely broken. Note
the significant difference in behaviour between carbon and metal. See Section 2. A, Understanding
metals in this Appendix. Even if the carbon frame was twice as strong as a metal frame, once the
carbon frame is overloaded it will not bend, it will break completely.
WARNING: Be aware that high temperature in a confined environment can affect the
integrity of composite materials, resulting in component failure which could cause you to lose
control and fall.
7.4.15 Inspection of Composite Frame, Fork, and Components
7.4.16 Cracks
Inspect for cracks, broken, or splintered areas. Any crack is serious. Do not ride any Gocycle or
component that has a crack of any size.
Delamination is serious damage. Composites are made from layers of fabric. Delamination means
that the layers of fabric are no longer bonded together. Do not ride any Gocycle or component that
has any delamination. These are some delamination clues:
1. A cloudy or white area. This kind of area looks different from the ordinary undamaged areas.
Undamaged areas will look glassy, shiny, or “deep,” as if one was looking into a clear liquid.
Delaminated areas will look opaque and cloudy.
2. Bulging or deformed shape. If delamination occurs, the surface shape may change. The
surface may have a bump, a bulge, soft spot, or not be smooth and fair.
3. A difference in sound when tapping the surface. If you gently tap the surface of an
undamaged composite you will hear a consistent sound, usually a hard, sharp sound. If you
then tap a delaminated area, you will hear a different sound, usually duller, less sharp.
7.4.17 Unusual Noises
Regular creaking noises such as in time with your pedalling, the wheels turning, or your regular
pulling or pushing, or bobbing of the suspension system could indicate loose or maladjusted
components or a problem. A well maintained Gocycle should be generally free of creaks and squeaks
that occur rhythmically with pedal, wheel, bobbing movements. Investigate and find the source of any
noise. It may not be a crack or delamination, but whatever is causing the noise must be fixed or
replaced before riding. Occasional creaks or squeaks or creaks or squeaks that are related to
lubrication or temperature variations or changes in humidity do occur with normal riding and as the
product ages.
WARNING: Do not ride a Gocycle or component with any delamination or crack. Riding a
delaminated or cracked frame, fork or other component could lead to complete failure, with
risk of serious injury or death.
7.4.18 Understanding components
It is often necessary to remove and disassemble components in order to properly and carefully
inspect them. This is a job for a professional bicycle mechanic with the special tools, skills and
experience to inspect and service your Gocycle to Gocycle's approved procedures.
7.4.19 Aftermarket “Super Light” components
Think carefully about your rider profile as outlined above. The more you fit the “shorten product life”
profile, the more you must question the use of super light components. The more you fit the “lengthen
product life” profile, the more likely it is that lighter components may be suitable for you. Discuss your
needs and your profile very honestly with your Gocycle dealer or Gocycle.
Take these choices seriously and understand that you are responsible for the changes.
A useful slogan to discuss with your Gocycle dealer if you contemplate changing components is
“Strong, Light, or Cheap –pick any two.”
7.4.20 Original Equipment components
Gocycle tests the fatigue life of the components that are original equipment on your bike. This means
that they have met test criteria and have reasonable fatigue life. It does not mean that the original
components will last forever. They won’t.