Aerodynamics of a convertible

[Cabriolet]

@0-40mph top up and down the vert gets the same mpg.
over 40mph. every 10mph with the top down you loose 1.5mpg vs having the top up.
with my hardtop on i get worse bumper to bumper than the soft-top up and on the freeway doing 65+ the hardtop gets better mpg than the soft-top.

IE @ 40mph i get 30mpg top up or down.
@ 70mph i get 22mpg with the top down, 26.5 with the top up and 27.4 with the painted hard top on.

[McGyver]

and no one thought to comment that e30s have basically zero aerodynamic stuff included?

aside from that, i would postulate that the top up would be better under the assumption that the the top would help to promote laminar flow, versus the turbulence created by the sudden loss of surface. but im also drunk.

[Dustn525]

I don't have a solid answer here since I'm at a bar, about 4 double rum & comes back, but when you have a long haired girl in the back seat with the roof down, her hair will actually blow forwards, it's funny when you know they spent a half hour straightening their hair before they asked you for a ride.

[Pl3wA]

i would say something like this

[Bearmw]

How about top down, windows up, windblocker up, eta front spoiler, and 225 series tires? Only scientific answers allowed.

[dnguyen1963]

Did you read the post about Ford testing their trucks? I do not think that any of us can tell a difference of 0.5 - 1% without sophisticated instruments. Regardless, tailgate down does not help fuel economy...period. With regard to convertibles, the fabric top would create a lot more friction than the top of a coupe so what you gain in aerodynamics with the top up would be canceled out by the friction. Put your hand on the top while driving at 60 mph and tell me what kind of turbulence the top is creating (keep in mind that I am talking about 20+ yrs old car - newer top might be very tight and acts similar to hard top).

[e30rapidic]

.37 top up (same as coupe)
.38 top down (due to the additional ladies wanting a ride and per Alpina testing)
.39 for ix

M3 is .33

[jeffnhiscars]

Now I have to know how much better the CD is with a painted hardtop vs a textured one. Anyone catch THAT episode on Mythbusters ?

@0-40mph top up and down the vert gets the same mpg.
over 40mph. every 10mph with the top down you loose 1.5mpg vs having the top up.
with my hardtop on i get worse bumper to bumper than the soft-top up and on the freeway doing 65+ the hardtop gets better mpg than the soft-top.

IE @ 40mph i get 30mpg top up or down.
@ 70mph i get 22mpg with the top down, 26.5 with the top up and 27.4 with the painted hard top on.

[turge]

It's a BIG difference top up or down. Top down going over 100 mph is like a wind tunnel. Massive drag and the car shakes like crazy. Ask me how I know.

Top up is much better if you want to take the car up to high speeds.

OP stop being stupid.

[Thizzelle]

read my comments. I never said "I was right and they were wrong"..only that they have punctured a hole in an age old belief but havent proven the opposite is true by considering all the variables. They are correct "on that day, with that truck etc etc"

What they do is rooted in science but is also somewhat tongue in cheek (ie infotainment)and def not controlled by any scientific standard.

None of it is conclusive regardless of what I've tested and agaim...just cause it's on tv doesnt make it so.

I'm waiting for someone to tell me Mr Rogers drove an e30 :-)

just stop talking please

[Vivek]

The principles have merit but I doubt a 79 F150 w an 8ft bed will get better mileage with the gate up.
\
Mythbusters busted :-)

read my comments. I never said "I was right and they were wrong"..only that they have punctured a hole in an age old belief but havent proven the opposite is true by considering all the variables. They are correct "on that day, with that truck etc etc"

What they do is rooted in science but is also somewhat tongue in cheek (ie infotainment)and def not controlled by any scientific standard.

Blue=wtf are you saying
Brown=shit you made up
Red=valid point

[semaj4712]

wow well if I have learned anything from reading this thread, science is not real, but rather whatever you think, must be correct

[F34R]

MB has its place in modern science and culture.

I did search it and so many comments reference Mythbusters, which means no one knows anything more than they see on tv. When you read how they did their test, it is totally unscientific and applies just to that truck on that day in that environment with those 2 drivers.

The principles have merit but I doubt a 79 F150 w an 8ft bed will get better mileage with the gate up.
\
Mythbusters busted :-)

Moron alert/

[Kershaw]

.37 top up (same as coupe)
.38 top down (due to the additional ladies wanting a ride and per Alpina testing)
.39 for ix

M3 is .33

why the hell does an ix have a higher drag CoD? the fender flares? really? or maybe the fact it has an i lip and not an is lip? any info there?

lowering the car is also good for a reduction in CoD. the lower the better, actually. that and the rear trunk might be why the m3 is much lower.

[e30rapidic]

why the hell does an ix have a higher drag CoD? the fender flares? really? or maybe the fact it has an i lip and not an is lip? any info there?

lowering the car is also good for a reduction in CoD. the lower the better, actually. that and the rear trunk might be why the m3 is much lower.

per the specs on e30world
ix's are 1400mm tall and 1661 mm wide
coupes are 1379mm tall and 1646mm wide
Since its the same shell, it has to be due to the amount of air going underneath?? I doubt the flares do much.

apparently the cabrio is only 1370mm tall. I would imagine that the solid roof has a little bubble to it that's higher behind the windshield?