Aerodynamics

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 Zipp’s 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.

The Aerodynamic Frame

(Below: Wind tunnel testing.)

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 ago.

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 race cars.

How Air Moves

There are four basic ways air moves around you on a bicycle...

• air moves over the top of your head
• 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 sapping energy.

The ZIPP Difference

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.

The Wheel Facts

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 drag.

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.