Engineering for speed means we have to take into account more than just the bike frame. We have to consider the three-dimensional space surrounding the bike and rider, including the downstream effects of airflow as the rider moves forward. This aero zone concept changes the whole design approach, and has allowed us to offer our riders a big jump forward in performance as a result.
When we study the position of the rider, the various bike components and their downstream effects, there are significant differences in airflow around different areas of the bike. Different flows call for different airfoils: just one foil, used everywhere, is not optimal. Designing a bike with different tube shapes in different zones can offer the athlete a significant speed advantage.
Examples of some aero zones can be seen in the CFD image above. The blue shows low velocity air movement, the red shows high velocity. You'll see that the handlebar is in relatively clean air. The head tube and fork are positioned within the wake created by the front brake. The down tube similarly is in the wake of the front wheel. The seat post and seat tube are in the wake of the athlete’s body. These are examples of what we mean by an Aero Zone: the entire design of the bike allows air to move around the bike and rider while creating minimal aero drag. For example, the lower part of the seat tube leads air onto the rear wheel; the fork crown and head tube guide air coming off the front brake.
What does this mean for our engineering process? Aerodynamic requirements are different in each aero zone. Using CFD analysis allows us to clearly see how airflow in each aero zone is different, and we engineer the various elements of our bikes to interact optimally with the specific conditions in that zone.