Coupes vs hatchbacks, what has less drag?

[fleabag]

I was looking at the Civic Hatchback for 1995 and the Civic Coupe for 1996 and I was reminded of something I was told very recently. The gist of it was that 80% of drag is caused by negative pressure behind the vehicle as it is moving, when the air moves over and below and aside the car, when they meet behind the car, they create unequal pressure from that of the front, creating drag which why SUVs are so much worse with drag than sedans. This idea was mentioned in an article discussing a CRX getting 95MPG by basically attaching a cone to the front and rear of the vehicle, covering the wheels and reducing the size from 195 to 185.

With this in mind, I was thinking about how hatchbacks are similar to Wagons and SUVs, when the air moves over the body, there is an abrupt transition at the back, this is less pronounced on a sedan.

So I was wondering, are Hatchbacks, or at least the Civic VX Hatchback '95 have more parasitic drag than a '96 Civic Coupe? How much? Has anyone evaluated this because I can't find anything about this on google.

 

[DivideBYZero]

Answer.

 

[Zenmervolt]

Oddly enough, it depends a lot on the car. For example, the Volvo 850 sedan has more drag than the 850 Wagon. Still, I think it is likely that in the case of the Civic, the sedan and coupe have less drag.

ZV

 

[nakedfrog]

Originally posted by: Zenmervolt
Oddly enough, it depends a lot on the car. For example, the Volvo 850 sedan has more drag than the 850 Wagon. Still, I think it is likely that in the case of the Civic, the sedan and coupe have less drag.

ZV

Geez, it would be hard for the 850 wagon to be shaped any MORE like a brick without cutting off the front...

 

[Zenmervolt]

Originally posted by: nakedfrog

Originally posted by: Zenmervolt
Oddly enough, it depends a lot on the car. For example, the Volvo 850 sedan has more drag than the 850 Wagon. Still, I think it is likely that in the case of the Civic, the sedan and coupe have less drag.

ZV

Geez, it would be hard for the 850 wagon to be shaped any MORE like a brick without cutting off the front...

I think that it's largely a function of the wagon being a little longer than the sedan and having a very mild taper at the rear. It shocked me too though.

ZV

 

[DivideBYZero]

Originally posted by: Zenmervolt

Originally posted by: nakedfrog

Originally posted by: Zenmervolt
Oddly enough, it depends a lot on the car. For example, the Volvo 850 sedan has more drag than the 850 Wagon. Still, I think it is likely that in the case of the Civic, the sedan and coupe have less drag.

ZV

Geez, it would be hard for the 850 wagon to be shaped any MORE like a brick without cutting off the front...

I think that it's largely a function of the wagon being a little longer than the sedan and having a very mild taper at the rear. It shocked me too, though.



ZV

This makes sense. In the late eighties Honda made much of the Accord Aerodeck and it's improved Cd that was due in part to the length of the roof area.

Aerodeck.

 

[JulesMaximus]

I doubt you'd notice much if any difference at all between one or the other in actual mpg.

 

[theeedude]

Drag is a big factor in mpg on highway. I have instantaneous mpg meter on the Mazda3, and there is a big improvement when tailgating a big rig or an SUV.

 

[JulesMaximus]

Originally posted by: senseamp
Drag is a big factor in mpg on highway. I have instantaneous mpg meter on the Mazda3, and there is a big improvement when tailgating a big rig or an SUV.

No shit, really? :roll: You follow a giant brick that is punching a big hole in the air and your fuel economy goes up?

Thank you for that informative post Capt'n Obvious.

Maybe all hatchbacks or coupes shoud come with their own big rig to tailgate...:laugh:

 

[The Boston Dangler]

Originally posted by: JulesMaximus

Originally posted by: senseamp
Drag is a big factor in mpg on highway. I have instantaneous mpg meter on the Mazda3, and there is a big improvement when tailgating a big rig or an SUV.

No shit, really? :roll: You follow a giant brick that is punching a big hole in the air and your fuel economy goes up?

Thank you for that informative post Capt'n Obvious.

Maybe all hatchbacks or coupes shoud come with their own big rig to tailgate...:laugh:

a few years ago, it was either road and track or car and driver, they entered a big elecrtic vehicle race, and won easily. their trick: each race car has a support vehicle- they used a ford excursion with huge air dams and drafted the race car inches behind it. at the time, perfectly legal.

 

[LS21]

generally, hatchbacks/fastbacks are more aerodynamic than coupes. note difference between COEFFICIENT of drag, which implies shape, and drag, which takes into account absolute size

unless 2 cars have different shapes / frontal profile, then we assume constant, ie 96 civic coupe vs civic hatch.. i would say hatch generates less drag and is more aero

some of the most aero production vehicles are : audi a3 (the big breadbox euro minivans... not the current US wagons), honda insight, toyota prius, etc...

national geographic has an issue on biomimetics where scientists/engineers mimic designs perfected in nature - one of the examples: a low-drag mercedes benz modeled after a coffin fish http://www.iom3.org/materialsw...back%20to%20nature.pdf

all more hatchback-like vehicles than coupes