Coefficient of Drag (for you Engineers out there) [Archive] - SaabCentral Forums

: Coefficient of Drag (for you Engineers out there)


1985 Gripen
19th October 2005, 07:00 PM
SAAB's aviation background has traditionally caused the car division to pay extra special attention to aerodynamics. The very first SAAB automobile prototype, the 1947 92.001 (http://www.saabusa.com/saabjsp/museum/cars.jsp) or "UrSAAB" (http://www.saabmuseum.com/ursaab/), was shaped with the aid of a wind tunnel and had an unheard-of-at-the-time coefficient of drag (http://en.wikipedia.org/wiki/Drag_coefficient) (Cd) of 0.32. That is a very good drag coefficient even today.

http://www.crosseuro.com/archives/Images/oldsaab1.jpg


The 1987 Classic 900 bumper redesign to a more integrated-style bumper and slanted grill/headlamps resulted in a drag decrease of 5%, leading to better fuel efficiency and reduced emissions.

Seeing the sleek new Mercedes-Benz CLS500 (http://www.edmunds.com/insideline/do/Drives/FullTests/articleId=105415) with its drag coefficient of 0.30 on the road today made me wonder how latter-day SAABs compare to the SAABs of yesteryear as well as to modern-day competitors in the aerodynamics department.

http://a332.g.akamai.net/f/332/936/12h/www.edmunds.com/media/roadtests/roadtest/06.mercedesbenz.cls500/05.mercedesbenz.cls500.r34.160.jpg


The current production car with the lowest Cd is the Honda Insight, I believe.

http://www.infoimagination.org/images_info/features/honda_300.jpeg


The record for a prototype car Cd was the 1985 Ford Probe V prototype (http://www.scottgrundfor.com/concept/1985probe.html). It had a Cd of 0.137. As you can see from the pictures below it was butt-ugly.

http://www.scottgrundfor.com/concept/images/1985FordProbe-concept2_t.jpghttp://www.scottgrundfor.com/concept/images/1985FordProbe-concept1_t.jpg


The latest car I've seen in a magazine with an ultra-low Cd (0.19) was based on nature's design for the boxfish. It is the 2005 Mercedes-Benz "Bionic Car" (http://www.germancarfans.com/news.cfm/newsid/2050607.004) concept.

http://www.germancarfans.com/news/2050607.004/2050607.004.Mini18S.jpg


Does SAAB still wind tunnel test their cars? Does anyone have a source of SAAB's as well as other manufacturer's coefficient of drag numbers?

900t
19th October 2005, 08:24 PM
The lowest Cd on a production car was the GM EV1 which was produced in 1997, 0,19. The "concept" which was aesthetically identical, the GM Impact of 1990, had the same drag coefficient.

1985 Gripen
19th October 2005, 08:52 PM
The lowest Cd on a production car was the GM EV1 which was produced in 1997, 0,19. The "concept" which was aesthetically identical, the GM Impact of 1990, had the same drag coefficient.

Thanks for the info. I'm wondering if the SAAB with the lowest Cd was the 1985 EV-1 prototype (http://www.saabmuseum.com/ev1/). Or did the UrSAAB have a lower Cd? There's no way to tell because I can't find a record of the Cd of the EV-1 anywhere on the web.
http://www.saabmuseum.com/photos/ev1_1.jpg

900t
19th October 2005, 09:37 PM
If I had to say, I'd say EV1.

That said, Saabs over the past few years were probably hovering around ,32 or so. Though I am sure a flat-front US headlamp C900 was pushing ,40. Even with the facelift and Aerokit I think it was still ,34 or ,33 - I have the numbers somewhere.

1985 Gripen
19th October 2005, 10:45 PM
If I had to say, I'd say EV1.

That said, Saabs over the past few years were probably hovering around ,32 or so. Though I am sure a flat-front US headlamp C900 was pushing ,40. Even with the facelift and Aerokit I think it was still ,34 or ,33 - I have the numbers somewhere.

Hey! I've got one of those C900s!;) Are you trying to claim that the 92, 93, 95, 96, and 99 had a lower Cd than the first-gen C900?

Seriously though, I'd like to see the numbers if you can find them.

1985 Gripen
20th October 2005, 01:57 AM
2003 9-3 SportSedan (http://www.webwombat.com.au/motoring/news_reports/3_11_saa.htm) - 0.28
2001 9-5 Aero Sedan (http://www.autorevista.com/articles/01saab95.htm) - 0.29
1999 9-5 Sedan (http://www.canadiandriver.com/testdrives/99saab9-5w.htm) - 0.29
1995 900 (http://www.internetautoguide.com/car-specifications/09-int/1995/saab/900/) - 0.30
2001 Viggen (http://www.autowire.net/2001-4.html) - 0.31
2000 9-5 SportWagon (http://www.thecarconnection.com/Vehicle_Reviews/SUVs_Wagons/2000_Saab_9-5_Wagon.S181.A842.html) - 0.31
1999 9-5 SportWagon (http://www.canadiandriver.com/testdrives/99saab9-5w.htm) - 0.31
1973 Sonett III (http://www.automotiveforums.com/t160291-saab_sonett_3.html) - 0.31
1947 92.001 prototype (http://www.saabmuseum.com/ursaab/) - 0.32
1967 Sonett V4 (http://www.globalcar.com/datasheet/Saab/1967SaabSonettV4.htm) - 0.32
1997 9000 Aero (http://www.cardomain.com/ride/858255) - 0.32
2006 9-3 SportCombi (http://www.automobilemag.com/reviews/wagons/0509_saab_93_sportcombi/) - 0.33
1999 9-3 (http://autoweb.drive.com.au/cms/A_51250/newsarticle.html) - 0.33 (0.31 of Viggen + 8%)
1997 900 SE Convertible (http://www.theautochannel.com/vehicles/new/reviews/1997/solo9725.html) - 0.34
1995 9000CDE (http://www.theautochannel.com/vehicles/new/reviews/wk9531.html) - 0.34
1986 9000 Turbo 16 (http://www.globalcar.com/datasheet/Saab/1986Saab9000Turbo16.htm) - 0.34
2005 9-2X Linear (http://www.carsdirect.com/research/saab/92x/2005/linear/features) - 0.35
1950 92 (http://www.saab.com/main/GLOBAL/en/pressreleases/archive/46/index.xml) - 0.35
1972 99 (http://www.saabnet.com/tsn/models/1972/techspec4.html) - 0.37
1984 900 Turbo 16V S (http://www.saabcentral.com/features/saab_900/press_reviews/motor_aero_t16s.php) (not sold in U.S. but sold as the "SPG" in '85) - 0.38
1987 900 (http://www.saabcentral.com/features/saab_900/press_reviews/motor_aero_t16s.php) - 0.39 (0.41 pre-facelift minus 5%)
2006 9-7X (http://www.autos.com/autos/sport%20utility/luxury/2006/saab/97x/42i/performance) - 0.40
1984 900 (http://www.saabcentral.com/features/saab_900/press_reviews/motor_aero_t16s.php) - 0.41

I'm embarassed to learn that my 1985 900 Turbo 16V has the worst Cd of any SAAB vehicle... EVER. And that includes the 9-7X SUV and cars manufactured in the 1950's! Ugh!;oops:

Just for fun, here are the Cd I could find on some of SAAB's modern day "competitors":

2006 Audi A4 (http://www.autos.com/autos/car/luxury/2006/audi/a4/20t/performance) - 0.33
2006 Volvo S60 (http://www.internetautoguide.com/car-specifications/09-int/2006/volvo/s60/) - 0.28
2006 Volvo V50 (http://www.internetautoguide.com/car-specifications/09-int/2006/volvo/v50/) - 0.32
2006 Acura TL (http://www.nctd.com/review-walk.cfm?Vehicle=2006_Acura_TL&ReviewID=1757) - 0.29
2005 Acura TSX (http://www.autobuyguide.com/2005/12-aut/acura/tsx/reviews/) - 0.27
2006 BMW 3-series (http://www.velocityjrnl.com/jrnl/2006/vmd10227sp.html) - 0.30
2006 Mercedes-Benz C-class (http://www.internetautoguide.com/car-specifications/09-int/2006/mercedes-benz/c-class/) - 0.27
2006 Audi A6 (http://www.automotive.com/2005/43/audi/a6/reviews/walkaround/) - 0.28
2006 Lexus ES 330 (http://www.kron4.com/global/Story.asp?s=3829464) - 0.28

Hummer H2 (http://en.wikipedia.org/wiki/Drag_coefficient) - 0.57

ragtopcav
20th October 2005, 04:47 AM
The lowest drag mass produced vehicle [until it was eclipsed recently by this new generation] was the Vauxhall Opel Calibra with a CD 0.26 - a euro j-type vehicle.

As far as Saab's go the ursaab was quite ingenious but if you look at the aircraft wing shape of it; now what do aircraft wings do? lift; I dread to think what the gust response of that car would be like :o . I'm not suprised about the old 900 not doing so well, the design is much to 'busy' a ruined 99 if you like.

So a very aerodynamic new 900 then, I'm enjoying this, Saab went back to there roots after the folly of the old 900 then with a bit of help from GM.

So we should contact that Volvo website/forum admin people and tell them that they cannot call themselves turbobrick anymore as it is the correct term for a C900 :cheesy:

edit

Volvo 850 [the turbobrick] has a CD of 0.29 to 0.31 depending on model/bodyshape

Cuba
20th October 2005, 06:43 AM
Do baked beans and bacon effect the equation?

Am I benefiting or loosing?

JAR
21st October 2005, 04:30 AM
1984 900 (http://www.saabcentral.com/features/saab_900/press_reviews/motor_aero_t16s.php) - 0.41

I'm embarassed to learn that my 1985 900 Turbo 16V has the worst Cd of any SAAB vehicle... EVER. And that includes the 9-7X SUV and cars manufactured in the 1950's! Ugh!;oops:

Hummer H2 (http://en.wikipedia.org/wiki/Drag_coefficient) - 0.57

Don't feel too bad, you beat the Hummer H2! And, a smooth brick at 2.1, you'll beat the brick in a race any day of the week and look better too.

Alex
21st October 2005, 07:25 AM
The Cd figure isn't that important anyway, a large change in Cd only has a small direct effect on fuel economy. Something like 10% off Cd for a 3% gain.

More important is the CdA figure which is the effective frontal area of the vehicle and comes from the actual area x Cd. The c900 scores quite well in this as it is a narrow car compared to many new ones, and will certainly have a lower CdA figure than a 9-7X.

Also important is the vehicle stability, something the original jelly mould Sierra got very, very wrong (and that was another aerodynamic vehicle). The 99 and c900 are both good in this respect.

SaabScott
21st October 2005, 07:53 AM
Do baked beans and bacon effect the equation?

Am I benefiting or loosing?

I think that would totally depend upon whether or not they were eaten together.:roll:

aeropilot
21st October 2005, 07:57 AM
As far as Saab's go the ursaab was quite ingenious but if you look at the aircraft wing shape of it; now what do aircraft wings do? lift :o .

Not quite, because an aeroplane wing has a corresponding profile on the underside, which the Ursaab doesn't have;)

kemosaabey
21st October 2005, 05:15 PM
My little old citroen AX has a 0.30 cd....

No official figure from saab on the c900 - and the 99's got progressively worse aerodynamically - though the combi was supposed to be better than the saloon....

volvo's (740, 240...) were around 0.43...

DanS
21st October 2005, 05:23 PM
when your speeds are low or your stuck in traffic. A car with a low drag doesn't get better mileage sitting behind another car or stuck at a light.

Increased engine fuel efficiency is more important than a low Cd in many circumstances.

A low Cd care would make a quiet fuel efficient highway cruiser.

Last_straw
21st October 2005, 05:43 PM
If they made an "Ursaab" replica today, I'd take out a large bank loan and buy one :cool:

900t
21st October 2005, 07:33 PM
makes sense in regards to the C900. Check out that windscreen! Also note how much wind noise you get at very high speeds.

1985 Gripen
23rd October 2005, 01:12 AM
The Cd figure isn't that important anyway, a large change in Cd only has a small direct effect on fuel economy. Something like 10% off Cd for a 3% gain.

More important is the CdA figure which is the effective frontal area of the vehicle and comes from the actual area x Cd. The c900 scores quite well in this as it is a narrow car compared to many new ones, and will certainly have a lower CdA figure than a 9-7X.

Also important is the vehicle stability, something the original jelly mould Sierra got very, very wrong (and that was another aerodynamic vehicle). The 99 and c900 are both good in this respect.

I don't have a source for CdA figures. Any suggestions for a guy who's (probably too) interested? I got to find something to redeem my old baby.

BTW, what's the reference to the Sierra you make?

1985 Gripen
23rd October 2005, 01:21 AM
If they made an "Ursaab" replica today, I'd take out a large bank loan and buy one :cool:

They'd never get away with selling a car with "suicide doors" today.;)

Alex
23rd October 2005, 06:23 AM
They'd never get away with selling a car with "suicide doors" today.;)

Mazda (RX8) and BMW (Rolls-Royce) do.

1985 Gripen
23rd October 2005, 02:24 PM
Mazda (RX8) and BMW (Rolls-Royce) do.

The few cars I've seen today which have "suicide-style" doors are designed so that it's the rear doors only and you have to open the front doors before you can open the rears. There's a Saturn sold here with a third door in that style.

Alex
23rd October 2005, 04:19 PM
The BMW RR has a special exemption which limits the car to a maximum speed of 2.5mph if the rear doors are open.

1985 Gripen
23rd October 2005, 11:23 PM
The BMW RR has a special exemption which limits the car to a maximum speed of 2.5mph if the rear doors are open.

Does it lock the doors at speed so they can't accidentally be opened?

Mattlach
24th October 2005, 01:52 PM
What I find really quite amusing about the Cd of the Ursaab was that they went through all that trouble of designing it in a wind tunnel, for a car that was going to have a top speed of 105km/h (65mph)

Seeing that aerodynamics have the best effect at high speeds... :p

1985 Gripen
24th October 2005, 03:01 PM
What I find really quite amusing about the Cd of the Ursaab was that they went through all that trouble of designing it in a wind tunnel, for a car that was going to have a top speed of 105km/h (65mph)

Seeing that aerodynamics have the best effect at high speeds... :p

The UrSAAB had an 18 horsepower, two-cylinder, two-stroke engine. Imagine how slow it would have been had it not been aerodynamically designed. That's like a go-cart engine! I'm shocked that that engine could propel a car that heavy to 65 mph.

I don't think that the aerodynamics were as much for top speed as for fuel economy.

UrSAAB engineer Gunnar Ljungström said (http://www.saabmuseum.com/ursaab/), "...if it can save 100 litres of fuel a year, it doesn't matter if it looks like a frog."

One of the unanticipated disadvantages of the aerodynamic design was the front wheels would trap snow. That's not good when you're driving a car in Sweden in winter.;)

Alex
24th October 2005, 05:25 PM
Does it lock the doors at speed so they can't accidentally be opened?

The rear doors do lock once the vehicle is moving. The BMW Mini also performs the same trick, once above 5mph the doors lock and stay that way until a button on the dash is pressed.

Mattlach
24th October 2005, 05:31 PM
The coefficient of drag?

http://www.theroostniteclub.com/images/David%20Barrus,%20%20%20%20%20%20Neil%20James%20an d%20Jay%20Whitehead%20beg%20in%20Drag%20Queens%20o n%20Trial.JPG

I'd say its about 3... :o