• Wind speed
• Wind direction
• Rider speed
• Wheel weight
• Pitch of the road (steepness of the road)

While lower weight is almost always better, and more aero is always better, often more aero shapes are taller and require more materials. Therefore, aero shapes are often heavier. So deciding on a balance is key.

Our first step was to determine the wind angle or yaw for which our wheel design should be optimized. You will design a rim different for a dead headwind than you would for a cross headwind. Through a lot of calculation and proof-of-concept testing with wind angle testing tools attached to the front of team bikes, we were able to calculate that the most common wind angle was a headwind of between 10 to 15 degrees of yaw. Remember that it's always a headwind, as we only pedal forward.

Now designing with a yaw angle in mind, we worked hard to reduce the total drag of the wheelsystem. All Aeolus wheels have 16 bladed spokes front and rear. This is the UCI minimum allowed for mass start events, and it still gives us a very stiff performance wheelset. The fewer the spokes, the less the air turbulence and resulting drag. We also decided to use only internal nipples, as the exposed nipples only add drag.

Second, we looked hard at surface preparations like dimpling. While they initially looked promising to create a turbulent boundary layer like on a golf ball, all benefits were lost when we looked at the trailing edge turbulence created by dimples on the opposite end of the wheel. Remember that wheels are both a leading and trailing edge, meaning that the wind hits the front of the wheel but also leaves the back of the wheel as well. The shape and surface construction of both are important and need to be considered together.

Next, we gave careful consideration to the interface between the tire and the rim/braking surface. These also need to be considered as a unit. Since the most common and most advantageous combination of durability and performance tubular tire is 23mm wide, we designed the rim to have an optimal aero shape with this sized tire. Using a 23 mm tire on a narrow 19mm rim and vice-versa is less aero that a tire/rim combination that works together.

The last question may be the most subjective. When is it appropriate to use deep-section aero wheels versus a lower weight, but lower profile and less aero wheelset like the Bontrager XXX Lite? For the sake of this discussion, let's say the winds are at a consistent angle and speed. The variables are the pitch of the road, the aerodynamics of the wheel(s), the weight of the wheel(s) and rider speed. So at what pitch should you switch to a lower profile rim?

It is best to look at the course of your race or ride. It is quite rare to have a race that is entirely uphill. Courses are typically a combination of flats, rollers, uphills and down. Usually the pure uphills, where your speed drops into single-digit miles per hour, will be a small fraction of the total ride. True, you may slow a bit on the uphill due to the added weight of the aero wheels, but chances are you'll go faster on the downhills and flats due to those same aero wheels and have an average faster ride on the deeper section Aeolus profile.