According to some people, yeah, it is.

The Duple 425 coach from the ’80s gets its name from its 0.425 coefficient of drag (Cd)—that’s a number aerodynamicists use to express how resistant an object is to moving through air.

You know what else has a coefficient of drag of roughly 0.425? A Lamborghini Countach.

But that doesn’t necessarily make them equally aerodynamic. One of the biggest differences between the two, of course, is sheer size, something that coefficient of drag, being a dimensionless quantity, doesn’t take into account. It’s almost sort of a meaningless number.

That’s why more and more aerodynamicists are talking less and less about Cd and more about CdA—coefficient of drag-area, which takes Cd and multiplies it by the frontal area of the vehicle to give you a real number, in square feet or square metres, that lets you compare drag a little better.


CdA is also the measurement we used in our latest quiz on aerodynamics. In it, we give you three cars and ask you to guess which has the best CdA and is, technically, the most aerodynamically efficient.


(Wherever possible we sourced our numbers from OEs or lifted them from various magazines’ wind tunnel tests, but we did have to rely on best estimates lifted from the internet for a few of them.)

Are you game? Think you can figure out whether a Rolls-Royce or a Jeep is slipperier through the air? Head on over to to take it, and feel free to post your score when you’re done—but no giving away answers!