frogbikes.com
Frog Bikes
Owner’s Manual
3
rd
Edition
2014
Fatigue
Fatigue is not a perfectly predictable science, but here are some general factors to
help you and your stockist determine how often your bike should be inspected. The
more you fit the “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.
Factors that shorten product life:
• Hard, harsh riding style
• “Hits”, crashes, jumps, other “shots” to the bike
• 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
Factors that lengthen product life:
• Smooth, fluid riding style
• No “hits”, crashes, jumps, other “shots” to the bike
• Low mileage
• Lower body weight
• Less aggressive rider
• Non-corrosive environment (dry, salt-free air)
• Clean riding environment
WARNING
: Do not ride a bicycle or component with any crack, bulge or dent,
even a small one. Riding a cracked frame, fork or component could lead to
complete failure, with risk of serious injury or death.
B. 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.
What are composites?
The term “composites” refers to a part or parts 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,
molded to form a shape. Carbon composites are light relative to metals. Steel weighs
7.8 grams/cm3 (grams per cubic centimeter), titanium 4.5 grams/cm3, aluminium
2.75 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.
Why use composites?
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 bikes. 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.
What are the limits of composites?
Well designed “composite” or carbon fibre bikes 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.
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 if the impact is hard enough the fork or
frame 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 a carbon frame is twice as strong as a metal frame, once the carbon frame is
overloaded it will not bend, it will break completely.
Inspection of Composite Frame, Fork, and Components
Cracks:
Inspect for cracks, broken, or splintered areas. Any crack is serious. Do not ride any
bike or component that has a crack of any size.
Delamination:
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 bike or component that has any signs of 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.
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.
APPENDIX B