When driving a convertable, how much drag does the vehicle experience at high speed, and how much does it effect MPG?

[Ryan]

I know that in a regular car, having your windows down creates a lot of drag, decreasing MPG numbers. I would assume this is so because as the air enters the car, the rear window stops it and forces the air back out, creating resistance. If you drive a convertable - say a Honda S2000 - would having the top down reduce MPG numbers? I don't think it would, since there is essentially, nothing to "stop" the air from moving like the back window of a non-convertable, but I don't know for sure.

 

[LAUST]

Like an AC Cobra?

 

[Cyberian]

I would imagine a convertible with the top down would create at least some additional resistance, just from the air entering the actual passenger compartment.
I would think that it would be almost neglible.

 

[Bekker]

I cannot answer your answer accurately, but I can tell you that the wind flow changes drastically at high speeds. Way back in the sixties I borrowed my uncle's Old's Holiday convertible (beautiful car indeed) and ran it out with the top down. Up to about 100 mph or so, the windflow went above the windshield as expected. Somewhere between there and 110 there was a sudden and drastic change .. the flow wrapped over the top of the windshield back down into the interior, sort of like a vortex. Blinded me because all the crap in the air went directly into my eyes. Believe me, I got off the gas fast. At that speed, milage was nothing anyway, but if anything, there was way more drag than with a non-convertible.

Bekker

 

[EMPshockwave82]

it's not hitting the rear window but it is hitting the back seat.. i'd still say there is enough drag to drop you 1 or 2 mpg minimum

 

[Ryan]

Originally posted by: EMPshockwave82
it's not hitting the rear window but it is hitting the back seat.. i'd still say there is enough drag to drop you 1 or 2 mpg minimum

What if there's no back seat?

 

[kaizersose]

drag is a fickle property and is directly related to a "shape factor" which is an experimental quantity unless you have some serious modeling software.

long story short - probably about 10% redux

 

[notfred]

Originally posted by: LAUST
Like an AC Cobra?

That's really not a convertible.

 

[Conky]

I drove my old '73 Delta 88 Royale with a 455 at over a hundred MPH and the thing that struck me the most at that speed was the noise of the wind. I couldn't hardly hear the stereo with it cranked all the way up. It was not that bad noisewise at 70 but the higher the speed was the worse the sound from the wind was. I couldn't tell you about the mileage because obviously I couldn't drive at that speed for more than a few minutes and that sucker guzzled the gas. Smiles to the gallon is what I got from that car!

 

[WinkOsmosis]

There is more drag because a vacuum is created behind the windshield, not to mention the turbulence. Why do you think hatchbacks are the most aerodynamic cars? The regular Corvette has lower drag than the Z06 with its notchback. Even if it was just a windshield and no seats and driver, there would be more drag. Air has to flow smoothly to have low resistance.