how areodynamic are convertibles?
 

hi

i just saw an add on telly for a convirtable and the angle from wind screen to back was about 12deg. i bet with a cap it would be pretty areo?

I suspect that convertables are only marginaly more aero than the average sport bike! Which is not that good.

convertible
 

The Karmann Ghia convertible,with top up,was one tick lower than coupe,0.38vs0.39.
It's the only example I know of where a convertible scored lower than hardtop.
Of course,with the top down,they're sky-scrapers.

I have access to a convertible. I think I'll run a test in a few days with the top up and the top down to see how the mileage is.

I have a convertible now as well.

Expect some aero testing and aeroshell prototyping later in the year.

I bet your bet is right.

The potential to reduce drag by aeromodding a convertible using a properly shaped hard top/tonneau is probably greater than the equivalent hard top car it's based on - at least within the vehicle's existing length.

And to address the question in the title of the thread, I sure wish I had my Hucho book (BEN! Bring it to the GGP in Watkins Glen next month please) there's an entire section about convertible aerodynamics.

Here's a neat tidbit: the drag coefficient of the convertible version (with the top down) of the world's most slippery-shaped production car is 0.14 higher than the coupe it's based on:


http://www.caranddriver.com/var/ezfl...cd_gallery.jpg

Source: 2011 Mercedes-Benz E-class / E350 / E550 Cabriolet - Official Photos and Info - Car and Driver

...short answer: NOT very aerodynamic!

...the late Fireball Roberts (of Daytona Beach fame) noted that the first races at Daytona raceway had two classes: convertibles and hardtops, but due to the "poor" aero of the open cockpits, nobody wanted to run convertibles...such that on race-day, French was "paying" drivers something like $2,000 to cut the tops off their hardtops and run them as convertables!

while driving with my boss in his audi A4 convertible we where dicussing milage. he has a friend who has the same car with the same engine but as a hardtop, and he noted that even with the top closed he got slightly worse milage on average than this guy. of course they may have a different driving style etc but the science is there to support these observations.