TECHNOLOGY STORIES BIKE INFO, GEOMETRY ... - Vintage Trek

Bontrager Wheelsystems
Bontrager Wheelsystems wheels set a new standard
in wheel performance. Bontrager Wheelsystems wheels are
light, fast, and rock solid, with a unique set of applicationspecific
features. Since different types of riding place different
demands on wheels, Bontrager Wheelsystems applies
the features to each wheelset which will optimize its performance
for that use. In other words, each wheelset draws on
the best specific set of the following possible features: paired
spoking, OSB (Offset Spoke Bed), front-or-rear specific rims,
top quality spokes (aero in some applications), and special
hub designs.
Engineered wheels
Bontrager Wheelsystems wheels are highly engineered;
every aspect of wheel performance has been considered,
and redesigned when necessary. An extensive battery of
tests has proven these to be truly outstanding products in
aerodynamics, low moment of inertia, and durability. Since
we proudly list the weights, it's easy to see the Bontrager
advantage in this parameter. But with Keith Bontrager,
durability is always a characteristic of paramount importance.
These wheels are no exception. The battery of tests
which every Bontrager wheel design must pass is truly
astonishing.
As an example, one torture test involves placing 300
pounds on the axle of a wheel, and rolling over fixed wooden
2x4s at 30 MPH. Don't try this at home! This test
regularly destroys many of our competitors wheels before
they meet our minimum standards. At the same time, we
insist that all Bontrager Wheelsystems wheels exceed them.
The key to durable wheels
The most important aspect of wheel building is achieving
even spoke tension, within a range of acceptable
tension. Certainly some of the responsibility here lies
on the careful hand-finishing applied to all Bontrager
Wheelsystems wheels. But even the best trained hands can't
achieve consistent, even spoke tension if the wheel hasn't
been designed properly.
Design review
When engineering wheels, every aspect of the wheel and
its components must be considered as a group. Rim design
effects lateral and radial stiffness, spoke bed strength, and
in extreme cases impact resistance. Spokes must be selected
with the right strength and elongation. Hub design must
provide support for the spoke head, and flange width effects
lateral stability. All the features must match up exactly to
optimize the design's strength-to-weight ratio.
The missing factor
On any bike, the rear wheel sees more stress than the
front wheel. The rear wheel supports a greater percentage
of the rider's weight. The rear wheel must accommodate the
freewheel or cassette, yet center the rim over the ends of
the axle. And while the front wheel can rotate during side
loading or deflection, the rear wheel is trapped between the
rigid chainstays. In riding, this can greatly increase sideloading
of the wheel.
Over the years, many approaches to increased rear
wheel strength have been taken. Rather than attempt to
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Trek 2002 Tech Manual
review all those here, we'll simply present the goal of the
Bontrager rear wheel; create the best possible balance of
spoke tension from the drive side to the non-drive side
of the rear wheel. Forget bracing angles, or distributing
the pulling load over more spokes. As we said earlier, the
greatest source of wheel failure is uneven spoke tensions.
Since the inherent design of a multi-speed rear wheel creates
a large difference in tension between left and right
sides of the wheel, the best way to create a durable structure
is to minimize this difference. Further, if a spoke is at
lower tension than its neighbors, it can't effectively apply
force to the rim.
Bontrager Wheelsystems rear wheels employ OSB
(Offset Spoke Bed) rims and special hub designs with a
more inboard left flange spacing. These features allow an
increase in the left-side spoke tension. The higher left
side tension allows the left spokes to apply torque transfer
to the rim. They also provide increased strength through
reduced lateral wheel flex. In other words, Bontrager
Wheelsystems wheels are more efficient.
Bontrager wheels create a more evenly-tensioned structure,
and thereby reduce the overall stress on the individual
components. The result is that Bontrager Wheelsystems
wheels offer unmatched strength and durability.
Bontrager Wheelsystems stay true longer
As your bike rolls down the road, your wheels are
loaded with your body weight as they turn. As they do,
the point at which the road resists the force of your body
weight is moving on the wheel. This moving force creates
a change in spoke tension such that every spoke on the
wheel is seeing a loose-tight-loose-tight-loose-tight cycle.
This cycle creates fatigue in the spokes, which will eventually
cause them to fail. In some cases, fatigue can even
cause a rim to fail. The greater the difference in spoke
tension within the wheel, the larger the variations in tension
through this cycle, and the greater the fatigue on the
wheel.
More immediately, long before parts fail due to fatigue,
the wheel may come out of true. As the tension is removed
from a spoke, the nipple can more easily turn on its
threads. This results in you spending more time working
on your bike, or having it serviced. With Bontrager
Wheelsystem wheels, the design creates more even tensioning.
Maintenance is therefore at a minimum.
The keys to a perfect road wheel
As we said earlier, Bontrager Wheelsystems employ
a set of specific features to achieve their high level of
performance. All wheels benefit from low weight, durability,
and low maintenance.
With road wheels, aerodynamics become very important
due to the higher average speeds seen on pavement.
One of the major influences on wheel aerodynamics is
spokes. Many Bontrager road wheels use aero, or bladed,
spokes to reduce wind drag. They also use reduced spoke
counts, relying on Paired Spoke Technology to maintain
high wheel strength with fewer spokes.
On a bike, the front wheel sees the most wind resistance
because it is the leading edge of the bike. The rear
wheel is "drafting the seat tube", and is in much more
turbulent air. For this reason, Bontrager road front wheels