At a press test of the Graves Yamaha Motorsports AMA Superstock championship-winning R1 a few years ago at Willow Springs, I was asked by an auto-magazine editor (who also happens to be a motorcycle enthusiast) why the Yamaha R1's bodywork didn't cover more of the rider for better aerodynamics. "No matter how tight you tuck in, I noticed the rider's knees still hang out the sides," he commented, adding that there wasn't "very much protection for the rider's helmet and upper body" even in a full-race tuck position. Why not just widen the fairing a bit to provide better coverage and aerodynamics?
I initially mentioned the problems associated with added frontal area (the overall silhouette of the machine as viewed directly from the front), but I soon recognized it was weak argument. One only has to look at an object like a jet airliner-which is obviously more aerodynamic than any motorcycle, despite being 1000 times larger-to realize that frontal area is only part of an object's overall aerodynamic efficiency.
Even though the most aerodynamic motorcycles in our "Tunnel Vision, Part II" test in this issue posted Cd (coefficient of drag, a number used to characterize the amount of aerodynamic drag over an object; the lower the number the better) numbers averaging around 0.47 with rider aboard, there are many economy-oriented, everyday automobiles with Cd measurements in the low 0.30s. A motorcycle with all its parts (including rider) exposed to the wind just has too many obstacles to make it as aerodynamically efficient as a car.
No, the real reason most manufacturers don't make their fairings more aerodynamic is styling concerns. The aesthetic appearance is hugely important in any motor vehicle purchase, and cars have the major advantage of being able to completely envelop everything but the wheels/tires. This gives the bodywork stylist much more freedom to design an overall package that can integrate much of an aero engineer's requirements yet still remain pleasing to the general public's artistic eye. A motorcycle, on the other hand, is far more limiting due to its smaller and narrower size (as well as its unique single-track wheel alignment). It has too many parts that hang out in the open, many of which cannot be completely covered by bodywork due to the need for movement while the machine is rolling down the road.
In fact, the biggest component of a motorcycle that cannot be covered by bodywork is the most important: the rider. Obviously, the rider needs enough room to move about the bike to assist in steering/handling, so confining him to one position-where he could be more aerodynamically integrated with the bodywork-isn't feasible. And then there is the problem of additional aero drag at the rear of the motorcycle caused by turbulence resulting from not keeping the airflow smooth once it's passed over the object. (This explains those big "bubbles" you sometimes see attached to the rear of big semi-trailer trucks.) With their all-enveloping bodywork, cars can manage airflow well past the rear wheels, unlike a conventional motorcycle.
Motorcycles are largely an emotional appeal. While cars can be as well, bikes usually don't have the utilitarian aspect that quite often is a major influence in an automobile purchase. Actually, even "logical" considerations like performance, comfort, and price can largely be forgotten when style and appearance take over a motorcycle buyer's decision process; one only needs to look at the cruiser sales phenomenon of the past two decades for ample evidence of that.
Straying too far from convention when it comes to sportbike styling can be a tricky tightrope to walk. And when it comes to incorporating aerodynamics, it's a risk not too many are willing to take. When Suzuki unveiled the Hayabusa, there was much heckling from the stylemongers who said they'd never buy anything so "ugly"; it's largely the bike's standard-setting performance that has made its somewhat unconventional appearance now acceptable, and why Suzuki hasn't touched its styling since day one (as well as incorporated some of the 'Busa's aero tweaks into its GSX-R series).
When Kawasaki was designing the ZX-12R (well before the Hayabusa's debut), a significant amount of wind-tunnel testing resulted in a final prototype whose styling was said to be "almost a carbon copy" of the Hayabusa. The engineers were happy with the performance, but when the product planners took one look at it, they quickly asked for a bodywork redesign, thinking that the prototype's then-unusual appearance would never sell. Of course, the Hayabusa has since proved them wrong, but most motorcycle enthusiasts probably would've agreed with the Kawasaki product planners' opinions back then. I know I would have.
As much as I care about absolute performance, there is still a part of me that wants a motorcycle to appeal aesthetically as well. Would I buy a sportbike that had aerodynamically correct bodywork similar to, say, the bulbous "dust bin" fairings used by the Grand Prix racebikes of the early '50s? Even if it had the best performance?I doubt it.