In order to measure frontal area, we photographed the Hayabusa and ZX-12R from the front, using a long lens to minimize parallax distortion, with a measuring stick beside each bike as a reference point. Later we scanned the photographs, enlarged them to an identical scale and close-cropped them. Using Adobe Photoshop, the pixels in the images were adjusted to a scaled half-inch-square size and then counted, which gave us an accurate measurement of the frontal area of each bike, confirming our impressions. The ZX-12R has a frontal area of 6.09 ft2 (0.566 m2), physically larger than the Hayabusa, which is 6.01 ft2 (0.558 m2). But the advantage for the Suzuki is not just in frontal area. With figures for both drag and frontal area, it's possible to calculate the coefficient of drag, which is 0.603 for the 12R and 0.561 for the Hayabusa. The winner of this wind tunnel shootout is the Suzuki.
It's worth remembering, however, that neither of these CD figures indicate a particularly impressive degree of streamlining, since even a typical passenger car has a CD of less than 0.60 and some models are lower than 0.30. A fully streamlined Bonneville speed-record bike might have a CD of 0.10. Such is the nature of streetbikes, where performance derives mostly from extreme power-to-weight ratios.
One of the most striking, and controversial, elements of the Hayabusa is its prominent, drooping snout. Is it possible this unusual shape contributes to the Hayabusa's more slippery aerodynamics? Not according to Cooper, who says one of the enduring misconceptions about aerodynamics is that a sharp, projectile-like nose produces less drag. He offers the example of a brick, which, once the leading edges have been smoothly rounded, can only achieve significant reduction in drag from changing the shape of its back end to minimize the wake size (the same reason a fairing that closes in is superior).
Motorcycles, even racing designs, continue to feature what Cooper calls "styling aerodynamics." A good example on the ZX-12R is the exaggerated torpedo shape of the mirrors, which Cooper says offer little, if any, advantage.
The most immediate way to decrease drag on a motorcycle is for the rider to adopt a crouched position. A smaller rider can produce a 15 percent reduction in drag; tight clothing, which reduces the "balloon effect," can provide another 15 percent reduction. Motorcycles generally have a large separated wake resulting from the unstreamlined shape of the rider, and are called "bluff bodies." Streamlined bodies have a gently closing tail and a very small wake, reducing the pressure drag. Motorcycles designed for speed-record attempts, and to a lesser extent racebikes, typically have enclosed shapes or bodywork that is integrated with the rider's body to produce a smoother wake. For streetbikes, however, styling conventions and comfort demands make this sort of approach impractical.
The next candidates for the wind tunnel test were the 1990 and 1996 Honda RS125 GP bikes. To look at the bikes, you'd expect the more current model to have the more slippery shape. The older RS has a blunter nose and a sharply cut-off tailsection, which don't "look" aerodynamic. But the wind tunnel proved otherwise, and the lowest drag was recorded by the older bike, with a CDA of 2.08 ft2 (0.193 m2) compared with 2.20 ft2 (0.204 m2) for the '96 model. The newer bike demonstrated a modest advantage in reduced side force, yaw and roll, but the '90 model had less drag at every wind angle. Cooper was unimpressed with the sharper and more aggressive-looking nose of the '96 model, but he suggested that the lower drag on the '90 model was probably the result of a better fit between the fairing and the rider