drag coefficicients for 88 300e

[Mercedes Fred]

using an auto encycloaedia (Auto Guide) from 1988, some cars are listed for comparison regarding their drag coefficient (Cd.) which seems to measure the aerodynamic properties (which can effect fuel efficiency, acceleration etc.)

88 MB 300e - .30 (listed as "remarkable" considering the squared stance)
88 Audi 90 - .30 (this model looks typicaly aero, egg-shaped)
88 Nissan 300 ZX - .37

some more 88 comps.:

jaguar Xj6 - .37
BMW 735/50 - .32
Honda civic crx - .32
alpha romeo 164 - .30
buick regal - ,30
porsche 928 - .34

[300EVIL]

Mercedes was the first to use areodynamic laser alignment on thier cars. they started with the 124 and 201 body style... Lucky Me!!
with the AMG body Kit on a 124 it's a CD of .25

[Ashman]

I think I remmebr reading somewhere that the 300E was .32 stock and that with the AMG kit it was .26. Now I forget where I read it, but it was just the other day I was reading up somewhere on wind tunnel's and benzes...

Alon

[FA22]

It's amazing that the ///AMG Kit cuts the CD by so much down to .25-6. That's pretty good even compared to todays cars. Would that incease in aerodynamics be a big enough differance to improve performance?

[Strider]

Originally posted by FA22
It's amazing that the ///AMG Kit cuts the CD by so much down to .25-6. That's pretty good even compared to todays cars. Would that incease in aerodynamics be a big enough differance to improve performance?

Well, with all things being equal, and if I correctly remember my fluid mechanics, the CD, or coeffecient of drag works like this in the drag force equation: Drag force (F), Cross Sectional Area (A), CD (Coeffecient of Drag, determined by an objects shape, cross-section to length ratio, etc), Relative velocity, or the speed of the car (V), and finally, Density (D), which is to say, the density of the fluid, air, which varies according to temperature and altitude. So:

F = CD*D*A*V^2. That is: Drag Force is equal to the Coeffecient of Drag times the Density (air) times the cross sectional area times the square of the velocity. As you can plainly see, the most dominant term of the equation is the velocity term, which makes the drag force exponentially increase. Assuming that the internal friction of the car's drivetrain and rolling resistance remain roughly constant at any speed (It does), and also assuming that the car is traveling on a flat road, then the force that the motor must overcome is totally dominated by the drag force at highway speeds. This is the sole reason why the national speed limit was set at 55 mph during the energy crisis of the 70s. It had nothing to do with safety, and everything to do with energy conservation. This was the threshold velocity at that time where the economy is optimized with the cruising speed, regardless of the drag coefficient for the most part, and most cars back then were one shape of box or another. (Or rather the point where the drag force vs. velocity curve really starts to become non-linear and exponential) For the majority of todays vehicles, that optimum velocity has probably been raised to about 60 with the large improvements made in drag. The differences in top speeds at say 160 vs. 165 mph for a car of the same shape is a huge difference in power of the motor. When Suzuki came out with the Hayabusa (The world's fastest production motorcycle, ever) with a clocked top speed of 194 mph, this was a huge kick in the crotch to the rest of the motorcycle industry, shredding the top speed titles previously held by the Honda Blackbird and the Kawasaki ZX-12. Suzuki did this by putting in a monster 1300 cc powerplant, then completely refining and optimizing their bike design in extended wind tunnel tests, resulting in a radically different looking sportbike which people either love or hate. Myself, having ridden my GPZ1100 for the last 5 years (no slouch in the power department), really long for one. Europe enacted a ban on any bike with a top speed over 186 mph now (300 km/h), so the industry complied and de-tuned the Hayabusa and ZX-12. (I tell you all, anyone who'll listen, there is absolutely no experience like riding a performance sport-bike. There isn't a car out there that can match the performance without going over a $100,000 budget to beat that $10,000 bike )

So anyway, with all things being equal, the cross sectional area being roughly the same after adding a front spoiler, (or only marginally larger), then a decrease in the drag coeffecient of 0.05 does equate exactly to a 5% decrease in drag force on the car at any speed, flattening out that exponential drag force curve somewhat. I guess in basic terms (ignoring the handling improvements), this could be looked at as a 5% increase in fuel economy at highway speeds and a higher top speed. (For the 20 mpg I typically get, this would increase to 21 mpg.)

Note that the downforce also increases with the spoilers, but for the most part this does not significantly add to the rolling resistance, which is STATIC friction.

Oh how I do love these engineering diatribes

[omegabenz]

300E is .30
300E AMG HAMMER with underbody pannels is .25
without pannels, .27

300CE widebody amg hammer with under body pannels was estimated at <.23

The S600 biturbo is .26 for this year.

Hope that clears everyone up.

[speedy300Dturbo]

0.30 sounds about right, for a stock W124.

[bobbyv]

Originally posted by Strider
F = CD*D*A*V^2. That is: Drag Force is equal to the Coeffecient of Drag times the Density (air) times the cross sectional area times the square of the velocity. As you can plainly see, the most dominant term of the equation is the velocity term, which makes the drag force exponentially increase.

the drag force increases with the square of the speed, which is a "geometric" increase, not an "exponential" one (i'm just being a nitpick here ...).

since Power=(Force x speed), the power to overcome the drag force at any speed is proportional to the cube of the speed.

if your car has a drag-limited top speed, then to double your top speed, you need 8 times more power (i.e., 2 cubed), just to overcome the aerodynamic drag, while not considering the frictional drag.

similarly, even a significant increase in power will result in an unexpectedly small increase in top speed.

the real number to watch out for (i.e. to minimize) is the "Drag Number", which is (DragCoefficient x FrontalArea), your effective frontal area.

other things to consider:
* adding a front spoiler can increase your frontal area, but may reduce the drag coefficient (although it is placed there primarily for downforce)

* lowering a car will cover up more of the tires from the front, reducing the frontal area by a small amount (admittedly negligible).

* wider tires increase the frontal area

* the drag force is the net result of the high pressure on the front of the car and the low pressure at the rear. Lower rear spoilers (i.e. under the rear bumper) can produce downforce AND reduce the drag coefficient, by lessening the effects of the low-pressure wake of the car (the new BMW 7series has this)

[ktlimq]

Ferrari 360 Modena F1
Cw-Wert: 0.33

Porsche Carrera GT
Cw-Wert: 0.39

Porsche 911 Turbo
Cw-Wert: 0.31

[omegabenz]

Originally posted by ktlimq
Porsche Carrera GT
Cw-Wert: 0.39

Maybe .29, no way its .39. If it was, I would be shocked.

It is possible though because it is a wide car, but it does have very smooth lines.

[ktlimq]

I think 0.39 is correct for Carrera GT.

They wanted high downforce rather than low drag coefficient.

[omegabenz]

Wow! I am very suprised.

Downforce:
343 lbs. @ 150 mph, with 459 lbs. drag
493 lbs. @ 180 mph, with 660 lbs. drag
640 lbs. @ 205 mph, with 857 lbs. drag
Aero. Balance @ 205 mph:
F: 192 lbs.
R: 448 lbs.

Lift-to-drag ratio: .75:1
Coefficient of drag: .39 (factory claim)
Downforce @ 205 mph: 640 lbs. (factory claim)
Reference area: 1.9 meters square
Calculated maximum speed: 213.4 mph (assumed 12% drive train and rolling resisitance power loss)

Information found from
http://www.mulsannescorner.com/data.htm