User Guide

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9
ZR9000
Is aluminum a new material?
It should be common knowledge that most
modern aircraft use aluminum exclusively for
their primary structures (internal frames and
bulkheads) and 95% or better of their exte-
rior surfaces, including load bearing skins.
The aircraft industry has been using these
alloys for many decades. The aircraft compa-
nies have picked aluminum because it offers
the best combination of material properties
and processing capability in order to create
high performance, light weight, robust air-
craft. So aluminum alloys have certainly
proved their long term durability and high
performance in the aircraft industry. The
occasional failure that has occurred has typi-
cally been due to a design or manufacturing
defect or improper maintenance.
Doesn’t steel resist fatigue better than
aluminum?
Occasionally we hear fatigue failure erro-
neously described as similar to the result
of bending a coat hanger back and forth.
This example is not relevant to the durability
or reliability of a bicycle frame. When you
permanently deform the coat hanger you
are yielding it. This has no relation to
fatigue strength. Some of the highest fatigue
strength materials (like carbon composite)
will not take a significant permanent set,
instead breaking at a high force level. So
carbon fibers, with extremely high fatigue
strength, would rate near zero in the coat
hanger test.
Compared to the better aluminum alloys,
a high strength steel alloy will exhibit a lon-
ger fatigue life at a high, fully reversing load
level. But remember, these numbers always
reflect performance for a unit volume. Steel
weighs 3 times as much as aluminum for
the same volume. In other words, if these
statistics were based on weight instead of
volume, steel would have to exhibit 3 times
the fatigue strength of aluminum to be con-
sidered stronger. It doesn’t. Steel is only the
better material if you don’t care how much
your bike weighs.
What are the benefits of aluminum in
bike frame construction?
Aluminum is a great material for bicycle
construction. Aluminum is light, strong,
economical, and relatively easy to make into
various tubing shapes, wall thicknesses, or
butting. Aluminum is also comparatively
easy to weld. Unfortunately, the better grades
of aluminum alloy require heat treating,
which is somewhat of an art.
When we say aluminum is light weight,
it’s more accurate to say aluminum is low
density. One cubic inch weighs one tenth of a
pound. Contrast that to steel, where the same
cubic inch weighs three times that amount.
This means you can use twice the volume of
metal that a good steel frame uses, and the
steel frame will still weigh 50% more than
an aluminum frame. And the lighter weight
positively affects the ride quality.
Aluminum can be easily made into tubes
which are shaped, butted, or tapered. It takes
a little extra work, but tube shaping and
butting can make more difference in the ride
of the bike than the material itself. By shap-
ing and butting the tubes just right, a good
designer can make a bike that is stiff where
it needs to be, yet comfortable. Used to its
optimum, an aluminum bike will provide an
outstanding ride.
Aluminum is also very strong. It is possible
to achieve significantly higher strength prop-
erties in the aluminum structure per weight
than in steel. Part of this comes from the
basic material properties. You can use more
material, and more easily form the material,
so you can put just the amount and shape
needed into the bike, and closely tailor the
amount of material to the strength require-
ments at the specific area. Proper placement
of the material within an extremely low
weight structure is critical. To create a
fatigue resistant aluminum bike frame, the
structure requires fairly thick material in
specific points. If you make the whole bike
frame thick, it will be heavy and have a dead
ride.
As with many other high-tech products,
the largest contributor to a high strength
bicycle frame is engineering and design. The
low density and high formability of alumi-
num allows tubing with increased wall thick-
ness, complex shapes and larger sections
where we want to achieve high strength
properties in the overall structure.
Aluminum is abundant around the planet,
so the raw material is comparably inexpen-
sive, especially compared to exotics like tita-
nium or beryllium. Since aluminum is rela-
tively easy to form, work, and weld, the final