Drag Coefficient and Drag Area

http://en.wikipedia.org/wiki/Drag_coefficient

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http://en.wikipedia.org/wiki/Automobile_drag_coefficient#Drag_area

Drag area is a variation of drag coefficient that allows you to directly compare drag including the effect of the frontal area. In the example above ducking down, as everyone knows, makes you go faster. This is not because you are a more aerodynamic shape (though you may be) it is because you are smaller (less frontal area). Drag area allows you to see the important factors as a single number and this tells you what vehicle will actually require less power to push through air.

Power to overcome Drag

Vespa Drag Measurements

To calculate drag, one thing you need to know is the frontal area of what is being pushed through air. Here are some area measurements roughly taken from a front on photo of a Vespa PX (no screen).

For more information see the simulated results when they are available at Vespa CFD/3D Model

Scientific Study

There is a 2002 scientific paper available called the Aerodynamic Investigation of a Scooter in the University of Perugia Wind Tunnel Facility

• scooters are normally road tested and not measured in wind tunnels
• 'A considerable influence on the aerodynamic behaviour of a motorcycle is exerted by the rider, which contributes to the frontal area of the vehicle'
• Considering the scooter by itself (i.e. no rider) the drag is low (which is good) and comparable to a motorbike
• At speed a scooter tends to lift more due to having less weight at the front. [Vespa Labs Note: The scooter tested had 39% load at the front, a Vespa PX has only ~20% with which means even less stability at high speed!]
• It is possible to use a NACA aerofoil to reduce the lift at the front

The paper references a few other interesting papers. These have not been read fully but the abstracts provide some clues:

The Effect of Handlebar Fairings on Motorcycle Aerodynamics 'cross-wind response may be reduced with a fairing or windshield mounted'

Useful Links

http://www.tonyfoale.com/Articles/Aerodynamics/AERO.htm

http://www.sae.org/technical/papers/ground_vehicle/AERDY

Motorcycle Workshop. Part 2: Aerodynamics

Tunnel Vision http://www.sportrider.com/tech/146_0106_aero/index.html

What makes the Suzuki Hayabusa faster than the more powerful Kawasaki ZX-12R? A visit to the National Research Council wind tunnel provides the answer - From the June, 2010 issue of Sport Rider. By Bruce Reeve