Why Titanium?
In the world of high performance bicycle frame design, there
are three primary materials being used today; titanium, carbon
fiber composites, and aluminum. All three materials have
properties that work very well in cycling. However the titanium
alloys 3Al/2.5V and 6Al/4V offer the greatest overall combination
of physical, mechanical, and chemical properties to
yield a frame with the best possible combination of durability,
ride quality, stiffness, and weight. And to understand exactly
why these titanium alloys work so well you need to first
understand each property and then more importantly how
they all interact together. There are seven primary material
properties which factor greatly in bicycle frame design:
Tensile strength is the basic measurement of strength of a
material. It is specifically a measurement of the force
required to pull apart a material. In frame design, the higher
the tensile strength the better. More strength allows less
material to be used thus saving weight.
Fatigue Strength
Fatigue strength is the measurement of how far and how
many times a material can bend before it breaks. High
fatigue strength is essential to the durability and safety of the
frame. Certain materials such as steel and titanium actually
have a threshold that if properly designed and used, can be
bent an infinite number of times without failure.
Yield Strength
Yield strength measures how much force it takes to permanently
bend a material. As with tensile and fatigue strength,
more is better. The very high strength levels of titanium once
again allows less material to be used which saves weight.
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Toughness
Toughness is the property that defines exactly how much a
material can stretch before failing. Titanium is an incredibly
tough material. Its toughness vs. weight ratio is one reason it
is used as armor in military applications. Aluminum has good
toughness as a raw material, but manufacturers have to be
careful when designing an aluminum frame to make sure to
not let the tube walls get too thin. Toughness is the achilles
heel of carbon fiber composites. If carbon receives an indentation,
fibers have most likely been severed, strength has
been reduced, and the possibility of further
fracture has seriously increased.
Density
Density is simply the weight of a material for a given volume
such as pounds per cubic inch or grams per cubic centimeter.
Of the three materials measured here, carbon is the lightest
weighing approximately .065 lb/sq. in. Aluminum is next
in line at .098 lb/sq. in. And titanium is actually the heaviest
at .160 lb/sq. in. The density of a material certainly is an
important factor in materials evaluation, but the more important
analysis for cycling applications is the material's density
relative to its strength and durability.
Elongation
Elongation specifically measures the percentage a material
will stretch before tearing or cracking. This is an important
property to evaluate when you're looking at bicycle frame
materials. You want a material that will give slightly before it
breaks. This in essence becomes a safety factor. Titanium
has excellent elongation (15% to 20%) while remaining an
extremely durable material.
Corrosion Resistance
Corrosion (or the lack thereof) plays a key role in the life
expectancy of your bicycle and influences the amount of
care or maintenance you must put into your bike to keep it in
good shape. Fresh water, salt water, sweat, hot, cold, ultra-violet
light, infrared light; none of these elements or conditions
will have any effect whatsoever on a titanium bicycle.
Conclusion
Each of these seven properties has a significant effect on the
performance of your bicycle frame. However it is crucial to
appreciate the collective contribution of all these properties.
Focusing on any singular property could lead to
inaccurate conclusions as to the overall performance of
your bicycle. |
