If you were designing a vehicle to be as aerodynamic as possible, it would definitely be counterproductive if parts of that vehicle actually moved into the oncoming wind. According to Los Angeles-based engineer Garth Magee, however, that's just what the forward-turning top sections of bicycle wheels do. His solution? Upper Wheel Fairings, which shield the spokes from the breeze. He claims that cyclists using his fairings can go up to 20 percent faster without any extra effort.
The exact physics by which the fairings are claimed to work are perhaps a little difficult for the layperson to grasp, but Magee explains them thusly:
"Under null headwind conditions, the wind is null at the bottom where the wheel is in firm contact with the stationary ground; and near the top the wind rises to twice the vehicle speed. By shielding the upper surfaces, the effective wind on the wheel is greatly reduced. And if a headwind is also present, the wind is reduced significantly more."
In road tests, cyclists using the fairings reported speed gains of 3 to 20 percent, depending on how much of a headwind was present. The fairings do add 2 lb (907 g) to the weight of the bike, although Garth maintains that the improvement in aerodynamics is well worth it.
And yes, full wheel covers and disc wheels do already exist. These can reduce stability by catching crosswinds, however, plus covers add extra revolving weight.
Upper Wheel Fairings, by contrast, are attached to the top section of the fork and seatstays, then finely adjusted in order to get the aluminum fairings themselves as snug with the sides of the wheels as possible – without actually touching them. Nylon spacers keep the fairings from damaging the rims, should they make contact due to wind gusts or vibrations.
Magee is currently raising production funds for his Upper Wheel Fairings, on Kickstarter. A pledge of US$199 will get you a full set, when and if they're ready to go. More information is available in the pitch video below.