In general, a good aero bike uses airfoil tube sections. This may seem obvious, but many “aero styled” bikes have arbitrary, “made-up” tube sections that can actually increase drag. In Cervélo’s early days, “aero sections” meant NACA (National Advisory Committee for Aeronautics) airfoils.
We still use some NACA foils where they make sense, but in our long quest to help Cervélo athletes go faster, we’ve spent enough time studying bicycle aerodynamics to not only design a family of our own aerodynamic sections (our TrueAeroTM library of airfoils) that improve on NACA for bicycle performance, now we’ve arrived at the next generation of aero design. We no longer design just a tube section (two-dimensional) – we now design entire bike frame skin surfaces (three-dimensional), taking into account the different air flow characteristic in each aero zone