The Squoval 3™ family of tube shapes is a direct descendant of first- and second-generation Squoval. The first generation of Squoval tube shapes were engineered in 2005 purely for high strength, stiffness and low weight. In 2009, second generation Squoval used new engineering technology gained in Project California to further lighten, strengthen and stiffen Squoval Cervélo models. Only afterwards, when tested in a wind tunnel, did we find Squoval frames had better aerodynamics than traditional round tube frames. By lucky accident, Squoval’s structurally engineered convex sides and corner radii were pretty good in the wind.
Relative aerodynamic drag. Aerodynamic drag is on the vertical axis, in multiples of a true aero shape. Each shape has the same frontal area, so the chart compares the drag due to shape only.
For many years now, we’ve used the above chart with the green shapes as a reference. Now in red, we’ve added a path showing an evolution from square, to radiused, to convex sides leading to the surprisingly low drag of Squoval™.
Could we improve Squoval? Yes! We:
- Sculpted the leading edges (down, head and seat tubes),
- Turned two ellipses by 90 degrees (lower seat stays) and
- Tweaked the corner radii (trailing edges).
Of these changes, sculpting the leading edge has the largest aerodynamic effect, and this change in shape reduces drag via two primary mechanisms:
- First, the when the leading edge is curved, more like a true airfoil, pressure on the leading edge is reduced: air flows more freely around an airfoil’s nose. This is evident in CFD analysis results as a reduced size of the red or orange coloured high pressure zones on the surfaces.
- In addition, the pressure on the surface is by definition normal to that surface – and Squoval 3’s curved leading edge means the pressure vectors do not point aft, as they do on a flatter, blunter leading edge, but at an angle from the bike’s direction. This is important because this angled pressure vector can be split into two component vectors, side force and drag, both of which represent less force than the normal pressure from which they are derived.
Thus, in addition to the first effect above (less pressure), the smaller drag component of the normal vector also reduces drag on the bike.
Most of Squoval 3’s airfoil leading edge is not perpendicular to the bike’s direction, so drag force is reduced: it’s a smaller component of the normal pressure vector.
Squoval 3 frame shape reduces aero drag by a whopping 74 grams (equivalent to 7.4 Watts) compared to second generation Squoval frames, without giving up any stiffness or gaining any weight. Now you can have your cake and eat it, too.