Trek 2002 Tech Manual
Accommodating the gender difference
For those who want the short version of what we
did to make the WSD bikes work for women, it's fairly
basic. We have designed and spec'd the WSD bikes
to provide narrower hand position, with grips and con-
trols adapted for smaller hands where possible. We have
placed the handlebars horizontally closer to the bottom
bracket, but higher. We use crank lengths appropriate
for a smaller person.
The changes may sound fairly basic, but we went
beyond what most have done. We wanted to make these
bikes ride as well for a woman as a man's rides for
a man. These frames are not just the connect-the-dots
approach of adapting a man's frame with women's parts.
We went the extra mile and changed the geometry to
increase overall riding performance.
We tuned the geometry for better steering, weight bal-
ance, and shock absorption. Achieving the right weight
balance is highly individual, but there are several com-
mon themes. First, you use your weight to push on
the pedals. Second, your weight helps hold you station-
ary on the saddle. Third, your weight balance over the
wheels is part of the complicated steering of a bicycle.
These different needs don't always agree on where your
weight should be placed; it's a compromise.
Have you ever noticed that when sprinting, you tend
to move forward in the saddle? Ever notice that your
bike is less stable when you sit upright `no hands'? Ever
try climbing really hard without touching the handle-
bars? To some extent, these examples illustrate how
weight distribution effects bike riding.
Anatomical differences between males and females
There are quite a few differences between men and
women that effect fit on a bicycle. All have some effect.
Some are more important than others. Here we make
comparisons between a man and woman of the same
overall height.
Body height- the distance from the floor to the top of the
torso (sternal notch). This distance is more relevant to bike
fit than overall height because the neck and head are not
accommodated by the contact points on a bike (the legs,
arms, and torso are). A woman's `body height' is greater
than a man's. Simply put, women have shorter neck/heads
than men. This means a woman of a given height will need
a slightly bigger bike than a man.
Body weight- the weight of the rider. Women tend to be
lighter than men. More importantly, the center of mass is
lower on a woman. A man's center of gravity is closer to
his shoulders, while a woman's is normally closer to her
hips. Since the torso is angled toward horizontal on a bike,
that means a woman's center of gravity on a bike may be
placed more rearward. To preserve good weight distribution
for handling and applying power to the pedals, a woman
needs to sit slightly further forward on a bike.
Shoulder width- the distance between the outside of the
shoulder blades (acromion of the scapulae). Although there
is little correlation between height and shoulder width,
there is a strong tendency for a woman of a given height
to have narrower shoulders than a man. The difference
is often 10 to 40mm. To apply mechanical advantage and
achieve good ergonomics, a woman needs narrower han-
dlebars.
Leg to torso ratio, arm to torso ratio Comparisons between
leg and torso lengths by gender, or between arm and torso,
are often made in attempts to explain gender differences
in bicycle fit. While there are some tendencies, both of
these comparisons exhibit scattered data. In other words,
between individuals there is lots of variation, but grouped
by gender, there aren't any strong conclusions to be
made.
Foot size- the shoe size of the foot. Women tend to
have smaller feet. Another important consideration is that
women more often exhibit over-pronation, which effects
pedaling biomechanics. While pronation is seen as an
inward rolling of the foot as weight is applied, the source
of this rolling is over-rotation of the tibia. As a result of
the misalignment of the foot and ankle in over-pronation,
women more often need orthotics. It's also important that
a woman's pedals allow rotation (fortunately most modern
pedals provide this).
Hand size- the width of the hand across the knuckles, and
the length of the fingers. Women generally have smaller
hands then men. It's also true that women generally have
less hand strength. To fit a woman's smaller hands, grips
should be smaller in diameter, and less width is needed.
To accommodate shorter fingers, controls should be closer
to the grips. However, the mechanical advantage of levers
on a woman's bike should be at least as great, if not
greater.
We do the best we can to fit our bikes to womens' hands,
but consumers demand certain components. Many popu-
lar items are simply not available to properly fit a woman
(yet).
Pelvic width- the distance between the sit bones (ischial
tuberosities). A woman's pelvis is wider than a man's. A
woman's saddle needs to be wider than a man's.
The arrangement of a woman's pelvis makes it difficult
for her to roll her pelvis forward on the saddle. Pelvic tilt
effects the angle of the lower back, so flattening the upper
back can put a sharp bend where the two meet. This can
cause pain, so a woman's handlebars need to be raised
slightly in an effort should be made to avoid sharp angles
to the back.
The ischial tuberosities aren't a single spot on the pelvis,
but curved sections of bone. They start wide at the back
and curve inward to meet at the center in the front of
the pelvis, sort of like two side of a triangle. As the pelvis
rotates forward, the part of the sit bones meeting the
saddle becomes narrower. The contact spots also move
rearward. As you sit more upright, the sit bones are
spaced further apart, but move forward on the saddle.
There are other important pelvic differences between a
man and a woman. A woman's acetabulum (hip sockets)
are further forward than a man's. In some cases, this
can make it look like a woman is overhanging the back of
the saddle. But it's really that her spine and tailbone (coc-
cyx ) is further behind her sit bones. It's an important
difference for ergonomics, since compared to the biome-
chanics of a man, this puts about 15% more stress on
a woman's lower back when lifting. Pulling up on the
handlebars requires the same lever system as lifting, so it
effects standing out of the saddle on a bike.
Positioning women
Handlebar position
Most current fitting systems are the result of study-
ing position commonalities of elite male road racers.
Rules like "get a flat back" are difficult for recreation-
al males, and with females it's even harder. Likewise,
similarly derived rules like "Knee Over Pedal Spindle"
or "the bars should cover the front axle" don't address
the biomechanics and ergonomics of females. As we've
discussed, the female body is different than the male
body.
Keys to fitting a woman on a bicycle
