Frontal area and drag coefficient of RS2?

[EspenW]

Do anyone have correct data for the drag coefficient and frontal area of the RS2?
I have seen anything from Cd of 0.28 to 0.35, would be interesting to see the official numbers

[Greenm3]

I spent along time looking for this data for my S2 and other vehicles, it iseems that manufactuers dont like giving out this information, i wanted it to use Reynolds number etc for uni but will ask my prof , he has lots of figures for all different vehicles. Hope I can help.
Michael

[S2central.net]

I have some ancient calcs on this from the past - based on common equations used by the drag strip folk to estimate ET and maximum speed from a car of known weight and horsepower and Cd. Google should find these equations again and these can be used to get a good estimate of Cd for an RS2 as we know its weight, power and max speed.

[BrianSmith_S2]

I think ive seen on google the S2 coefficient of drag quoted around 0.32

I's guess the RS2 would be similar, but ever so slightly higher due to fatter tyres, and front bumper.

[UrS4boy]

Do anyone have correct data for the drag coefficient and frontal area of the RS2?
I have seen anything from Cd of 0.28 to 0.35, would be interesting to see the official numbers

The August 3, 1994 issue of AutoCar & Motor quotes a Cd of 0.35.

[HPmuirt]

I think ive seen on google the S2 coefficient of drag quoted around 0.32

I's guess the RS2 would be similar, but ever so slightly higher due to fatter tyres, and front bumper.

I too have seen 0.32 quoted by Audi for the S2 (trying to find the actual doc now) but why do you think the RS2 bumper would be worse compared with the S2?

Cheers n

Si

[S2central.net]

Ah-Hah... FOund it - fill your boots with this XLS that I built from those dragstrip calcs that I found in the past. You can reverse engineer these calcs to estimate Cd and frontal area (Fa) for the S2 and RS2. Fa should be somewhat measurable though.

[BrianSmith_S2]

I too have seen 0.32 quoted by Audi for the S2 (trying to find the actual doc now) but why do you think the RS2 bumper would be worse compared with the S2?

Cheers n

Si

Apart from the less fussy rear end of the coupe to the estate and the wider tyres, the bumper is the only other real difference between the RS2 and S2. I may well be wrong tho. maybe the bumber doesnt add anything to the Cd, but instead, as its larger adds to the frontal area of the equation

Fluid dynamics were not my strong point at university, but i seem to remember the overall effort of pushin the car through the air relies on
Cd (coeffeiecient of drag) x Ca (frontal area)

[S2central.net]

The only fluids I studied at Uni had froth on them - in the glass or at the gash - I'll edit that later

[BrianSmith_S2]

The only fluids I studied at Uni had froth on them - in the glass or at the gash - I'll edit that later

[Keeper of The Kitten]

First thing to understand - Cd changes with airspeed.

Second thing to understand - manufacturers always quote a low Cd for marketing reasons, so they'll choose an airspeed that gives a nice low value.

Third thing to understand - yes, CdA is more important than just Cd. Manufacturers do shy away from that.

Any additional air ducted through a heat exchanger (eg intercooler) will usually have detrimental effect on drag. I would be quite prepared to accept that the larger intercooler and associated larger intake opening of an RS2 bumper could potentially make things worse in that respect.

Unfortunately air doesn't tend to do exactly what you think it's going to do.

If I was going to make any assumption, I would say the rounded leading edges of an RS2 bumper might cause more lift than the squarer chin on the S2 bumper.

But that's not really accounting for the rest of the car that follows it.

[EspenW]

The August 3, 1994 issue of AutoCar & Motor quotes a Cd of 0.35.

Yep, the 0.35 number quoted in that legendary (0-60 in 4.8) test is what caused me to investigate this. I have used 0.32 and 20.4sqm when doing tests with my Mr.Dyno accelerometer. The RS2 bumper is bigger, but it sits lower, so drag from flow under the aerodynamically dirty underside of the car is reduced. However, as someone else mentioned, tires are bigger, and that might very well account for much of the difference. Avants also have more drag than coupes and sedans.

[BrianSmith_S2]

Yep, the 0.35 number quoted in that legendary (0-60 in 4.8) test is what caused me to investigate this. I have used 0.32 and 20.4sqm when doing tests with my Mr.Dyno accelerometer. .

20.4 sqm is way too large for frontal area as the width and height of the RS2 is as below

Width 1716 mm
Height 1375 mm

should it be 20.4 sqfeet??

[S2central.net]

sqft yes - I arrived at 20.4 with some rough estimation also.

[EspenW]

20.4 sqm is way too large for frontal area as the width and height of the RS2 is as below

Width 1716 mm
Height 1375 mm

should it be 20.4 sqfeet??

Absolutely correct, sqft it is