Courtesy of Yamaha

MotoGP Aerodynamics Continue To Evolve During Sepang Preseason Testing

Understanding motorcycle stability at very high speeds

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motorcycle’s steering geometry is predicated on its weight distribution while sitting still, but the faster the bike accelerates and the higher the speed it reaches, the greater become forces that remove weight from the all-important front wheel. The force accelerating the bike operates at pavement level, but the center of mass of bike, fuel, and rider is located nearly 2 feet above that. Multiply rear wheel driving force times that lever arm to get a torque tending to reduce the load on the front tire.

Repsol Honda riders Dani Pedrosa (26) and Marc Márquez (93)
Repsol Honda riders Dani Pedrosa (26) and Marc Márquez (93)Courtesy of Honda

The other force is aerodynamic drag, which, like accelerating force, acts well above ground level. Because bikes have short wheelbases, aero drag literally tries to blow them over backward. I saw Mike Baldwin on his Yamaha TZ750 crest the rise on Mosport Park's (now known as Canadian Tire Motorsport Park) old back straight, causing his front wheel to suddenly reach for the sky.

“I had to go for the back brake to bring it back down,” he later told me. An amazing number of people seem to think an anti-wheelie system solves all such problems, but anti-wheel operates by cutting throttle.

But why build 250 hp into a modern MotoGP bike just to chop its throttle? Like Peter Ustinov as "Commendatore Fanfani" on his great recording, "Grand Prix of Gibraltar," says, "Any fool can make a machine go slow. But it takes a genius to make it go fast!"

Movistar Yamaha riders Valentino Rossi (46) and Maverick Viñales (25)
Movistar Yamaha riders Valentino Rossi (46) and Maverick Viñales (25)Courtesy of Yamaha

In the case of MotoGP, the geniuses came up with winglets—arrays of stubby wings attached to the forward part of a motorcycle’s fairing. They were intended to produce downforce that would allow acceleration to continue past the point at which rear tire thrust would normally lift the front wheel. You win races not by chopping throttle but by being able to use more of it.

There is another purpose for winglets: to enhance stability at very high speed. As a MotoGP bike accelerates at 200 mph, something close to half the normal load on its front tire has disappeared. Continued acceleration and blow-over-backward forces exert the torques that cause this. The rider feels that the machine is less stable now. The front tire’s footprint has shrunk, and shrinking with it are the essential damping forces that normally suppress steering oscillations.

Ducati Team riders Jorge Lorenzo (99) and Andrea Dovizioso (04)
Ducati Team riders Jorge Lorenzo (99) and Andrea Dovizioso (04)Courtesy of Ducati

Could the right sort of bump knock the front tire off the ground and also give it a kick to one side? If that happened, the machine would be presenting part of one side to tremendous wind pressure. The result would be a sudden torque tending to make the bike switch ends. Riders feel everything, and this kind of feeling doesn’t inspire confidence.

That’s why rider comments following the just-completed Sepang preseason MotoGP test praised the latest downforce fairings for: 1) suppressing wheelies and thereby allowing continued strong acceleration; and 2) increasing stability at very high speeds. What they liked less was also predictable: 1) because the generation of lift also generates drag, there is some loss of top speed; and 2) in fast corners the large aero downforce becomes push-you-off-the-corner force because of the bike’s lean angle.

Team Suzuki ECSTAR riders Andrea Iannone (29) and Alex Rins (42)
Team Suzuki ECSTAR riders Andrea Iannone (29) and Alex Rins (42)Courtesy of Suzuki

The original winglets were banned because of concern that their obvious knife-like shape might injure someone. So today’s winglets are located in a gap between an outer wall and the fairing’s side-of-nose contours, rendering them harmless to human beings and pets. These “ducted winglet” fairings are given names such as “hammerhead,” “cheese grater,” etc., in line with the rule that all specialized human activities are entitled to their own jargon. Such fairings may be useful to riders on courses where the right combination of front wheel lift and/or very high speeds are present. As we saw last year, not all riders chose to use downforce fairings so unadorned shapes were also in common use.

Last year the jury remained out on ducted winglets. Will this year’s versions prove decisively better?