2002 Trek Technical Manual
For the 2002 model year, we are introducing something
new to the bicycle industry- a frame material designed spe-
cifically for the manufacture of bicycles. We call it ZR9000.
Like some of our competitors, we can wax eloquent
about various laboratory tests of strength and stiffness.
Often, a new material is used as a reason to substantially
raise the price of a bike. But as we've said before, the
ride of a bicycle is the sum of its design, manufacture, and
material, in that order. In other words, its not the material,
but what we do with it that makes a bike ride better.
A great frame material should allow the designer to
make a better bike. If a frame isn't lighter, better riding, and
at a better value to you, where is the benefit from this new
wonder material?
So the proof is in the finished product. Our models
using ZR9000 are up to 190 grams (almost 1/2 pound)
lighter than last year. At the same time, they are stronger,
and have a fatigue life up to 5 times that of the comparable
2001 models. And we can deliver these awesome new bikes
at approximately the same cost to you.
For some, knowing you are buying a lighter, stronger,
longer lasting bike at the same cost is enough. But we know
some of you want to know more about this technology. To
explain in more detail, we've asked the developer of ZR9000
to say a few words:
A MATERIAL DESIGNED FOR BICYCLE
FRAMES.
by Gary Klein
Advertising Claims
I'll bet you are thinking: "Just what we need, another
new bike frame material! Isn't the field crowded and confus-
ing enough as it is? Are all of the various frame materials
really different? Do the differences really matter? How can
every material be superior to every other one? Or are they
just marketing hype?"
Which of the claims from which companies should you
believe? Most of the advertised properties for different
frame materials are the properties of a material in its high-
est temper state, made into little coupons and tested in
laboratory machines; not the strength that the frame mate-
rial is in after it has been made into frame tubes, and
welded or brazed into a bicycle frame. The material may
chemically be the same, but the advertised strength is not
there.
In addition, and more to the point, the advertised
strength is a bulk material property and does not reflect
the engineering design of the bike, such as the diameters,
wall thickness, and shapes of the tubing used. These have a
huge influence on the overall strength of the finished frame,
and at least as much influence on the way the bike rides.
Please do not equate advertised material properties with
frame durability, performance or low weight. If you want to
compare the strength of one frame to another, you probably
need to test them both. And if you want to compare the ride,
instead of looking at charts you'll need to ride them!
Why Aluminum?
In the early 70's, when I lined up on my first starting
line, the bikes around me weighed an average of about 22
pounds. My Fuji Finest was at least average in quality, yet
the frame represented the heaviest part of the bicycle. Even
so, I found that it was not stiff enough to keep the drive
train in alignment during sprinting efforts.
At the time I was a student at MIT in Boston,
Massachusetts. A professor, myself, and some other stu-
dents started to look at what would make a better material
for bicycle frames. The standard high-end bicycle frame
was made of double-butted chrome molybdenum steel alloy
tubing. Steel is easy to work with, but it is very dense,
making even the thin tubes of my high-end steel racing
bike into a heavy structure.
Our goal was to make the frame lighter, stronger and
stiffer. To meet those goals, our first criteria was a material
less dense than steel.
As lower density alternatives, we looked at Aluminum,
Magnesium, Titanium, and Carbon fiber. While each of
these looked like they might provide some benefits, we
were also looking for an easy way to make a few bikes. We
were hoping to find a material that we could obtain easily,
and assemble into a strong and light frame.
Carbon fiber needs special molds for each size and
geometry of frame to be produced. This would take time
and cost a lot of money for prototypes.
Titanium was very expensive and the welding was dif-
ficult. The entire area being heated needed to be shielded
from air. Even ignoring the cost, it was difficult to obtain
in the tubing sizes we needed for bikes. Most available
tubing was CP (Commercially Pure) titanium which did not
provide much of a strength benefit.
Magnesium has the lowest density of the metals we
looked at. Initially Magnesium looked good, with relatively
high tensile strength per weight, but it does not have the
ductility of aluminum, and does not weld as easily. Also the
tubing sizes we needed were not readily available. Another
problem was this was in the Boston area, where the streets
are salted in the wintertime. We had seen what the salt
does to a steel frame, and we knew that magnesium has an
even lower resistance to corrosion. So it would need a real
good protective coating.
After our research, we decided on aluminum as the
material of choice. As we wanted the highest performance
frame possible, we started looking at the highest strength
aluminum alloys. Unfortunately, they were difficult to weld,
to form, had corrosion problems, etc..
Materials that were strong, but not weldable, would
create the need for special bonding lugs at each joint.
These would have to be designed and machined individu-
ally for each frame design, a somewhat daunting task. So
we looked for a material where we could create a high
strength weld with normal welding methods.
Finally we settled on 6061 aluminum. It came the
closest to meeting all of our frame material goals. 6061
was the workhorse of the structural aluminum alloys, and
it had most everything we desired. It is easily welded,
machines easily, is formable at room temperature, and
resists corrosion pretty well (it is used extensively for
marine applications). As a real plus, 6061 was used exten-
sively in aircraft, so thin wall tubing was readily available
in various diameters.
Aluminum
Pure aluminum is very soft. The molecules align and
interconnect such that in pure aluminum, molecular slip-
page easily occurs in all three directions (slip planes). As a
ZR9000
