Aerodynamic efficiency is affected
dramatically by you, the rider. You are 80-90% of the total drag on a bike and
rider combination. This is the primary reason for you to spend as much time as
possible being fitted to your bike correctly in order to maximize your power
output and not negate any of this effort through poor aerodynamic position.
After you have taken this significant step, you need aerodynamic wheels. If you
have never ridden a pair of Zipps on your bike, you will not have had the
thrill that lightweight, aero, high performance wheels can give you or the
improvement they can make to your overall time.
(Below: Wind tunnel
When the safety bicycle was invented
in 1885 by English bicycle manufacturer J.K. Starley, little thought went into
aerodynamics. The focus then was on creating a functional frame for two wheels
of equal diameter. Incredibly, most conventional bicycle frames today are a
derivative of the old-fashioned diamond geometry invented over 110 years
Today, advancements in aerodynamics
and wind tunnel studies show us that the diamond frame does nothing for
aerodynamic efficiency. Drag is generated by increasing turbulence behind the
rider. The faster the rider and bike move the more turbulent the air, the more
drag produced and the greater the adverse effect on speed.
The shape of an object moving
through air also affects the drag produced. The shape has to gently part the
air, then allow air particles to easily reattach. Ideally, an "aero
shape" should have a rounded or smooth leading edge and a very small and
sharp "trailing edge". For example: airplane wings, blimps and solar
Rider on conventional bike.
Rider on ZIPP bike.
There are four basic ways air moves
around you on a bicycle...
- air moves over the top of your
- air moves around your right side
- air moves around your left side
- air moves around the bicycle
frame, between your legs, under and behind you.
Drag caused by air traveling over
the top and on your sides can be reduced by an aero position, a sleek helmet
and aero bars. But a lot of drag, not so easily reduced, is created by the air
moving underneath and subsequently behind you. Traditional seatstays and
seatposts act as an eggbeater creating air turbulence, slowing speed and
ZIPP bicycle frames reduce drag.
This is because there is no seat tube, seat stays, or rear brake. Air flows
between your legs and reattaches more easily behind you.
Bottom line: you can ride faster
without expending more energy. In fact, wind tunnel tests show that at 30 miles
per hour, a rider in an aerodynamic position riding a ZIPP bicycle will expend
18 percent less effort than on a traditional diamond frame.
Wheels are secondary only to frame
design in factors that effect drag.
Most experts agree that a flat, solid disc wheel is the
most aerodynamic. That's because disc wheels don`t have spokes that cause
turbulence and the resulting drag.
Similarly, deep rim wheels are
aerodynamic not only because of their shape, but due to the shorter spoke
length. The outer perimeter of the rim is the fastest moving part of the wheel,
therefore by shortening spoke length we decreased turbulence resulting in less
Also by using a stiff material like
carbon fiber, the number of spokes on a deep rim wheel can be reduced. Thus a
cyclist with a pair of "standard" 32-spoked wheels can safely ride a
deep rim front wheel with only 18 spokes, and depending on body weight- a deep
rim rear wheel with 24, 28 or 32 spokes.