Spokes are generally the last thing that you pay attention to when buying a new wheelset; manufacturers know this and try to make a little extra profit by using second-class components.
It's nothing wrong if one spoke is of inferior quality - but if each wheelset has 36 spokes, you end up with more holes than a Swiss cheese.
Spokes bind the hubs with the rim; they transfer all the energy and power of the rider to the rim and via the tires to the surface. Since spokes travel from the hubs all the way to the edge of the rim, they are heavily exposed to air streams and form a big part of the aerodynamic drag. This drag depends on the number, length and form of the exposed spokes.
Logic says that fewer spokes produce less drag and make a more aerodynamic wheelset.
Example of a wheelset with less spokes and with stiffer, more aerodynamic carbon rims, which makes them also very light.
Wheelsets with deep section rims can have less spokes, since higher rims are also stiffer (this is highly appreciated by sprinters at the end of a fast stage, where they achieve their power-output peaks. Deep section rims oblige with high stiffness and light weight due to the use of carbon fiber.)
SPRINTING - high speeds and high power output call for a very reactive rim
An ideal spoke is therefore very aerodynamic and...
I have photographed cross-sections of some spokes - images speak louder than words.
Spoke cross-sections - round ones are cheaper, but they still serve their purpose. However, profiled or flat spokes should be used if you're after speed. Let's compare the widely used flat spokes with the round ones in terms of aerodynamic drag.
These details are notable only at high speed (above 45 km/h); however cheaper spokes are heavier and of inferior quality.
DT SWISS CHAMPION 2mm round
SAPIM LASER 1,5mm round
AERO Pillar 1x3mm flat
SAPIM CX RAY profiled - once these spokes are tuned to high tension they cut like a blade.
You can see how the Cx Ray spoke is rounded. Weight of a single spoke is cca 4,6g or some 200g for a wheelset.
Cheaper flat aero spoke - flat surfaces cause turbulences which in turn increase the drag. Weight of a single spoke is cca 6,5g or just above 280g for a wheelset.
VIDEO of vortex formation behind a round body. Entry angle of air plays a significant role in aerodynamics (not for round spokes since their form is the same from all sides).
Airstream simulation for round surface body
Once the air starts to flow from an angle the aerodynamics decreases drastically. Therefore the wheelsets of the new generation (LIGHTWEIGHT FERNWEG, ENVE SMART; ZIPP FIRECREST etc) are wider and rounder, thus coping better with lateral airstreams (side wind).
Drag coefficients for different shapes
Spokes are the most strained components of a bicycle (even when the bike is resting in your living room, set to OFF, there are significant tension forces acting through the spokes; namely to the hubs and the rim. Therefore the spokes must be strong and sinewy).
There is little room for error, also when building a wheelset. Every spoke must be perfect! Sapim, DT Swiss and Wheelsmith spokes are known to come the closest to this perfection. Wheelsmith's are said to be the best but since we don't have much experience with them, we use Sapim's, a world-wide proven quality product.
Sapim offers the most advanced spoke at the moment, aptly named SUPER SPOKE. Its main quality is high strength at a light weight.
Sapim's flagship is aerodynamic spoke CX Ray.
Besides its elliptical flat shape it boasts a very low weight and high elasticity. In its core it is a round 1,5mm Sapim Laser spoke that has been rolled and thus acquired its aero shape and extra elasticity. It goes without saying that the price of these spokes is somewhat higher than with basic round spokes.
Several manufacturers use flat "aero" spokes, but they are of inferior quality and therefore cheaper.
Next time, when admiring a polished high-end wheelset, it is worth finding out which spokes connect hubs to the rim; and how these wheelsets were built.