Coefficient of Drag
Thread Starter
6th Gear
Joined: Sep 2002
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From: Carmel Indiana
Coefficient of Drag
I'm trying to get confirmation of the CD number for my 1992 C4. In a discussion with the designer at GM during a club meeting I thought he had said it was 24 but that was sometime ago and the memory isn't the first thing that goes or maybe it is.
Instructor
Joined: Dec 2008
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From: Atlanta GA
Instructor
Joined: Nov 2003
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From: Ringgold GA
Going off memory from a few years back but remember reading something about the C3 Vette being about .44cd and the new vette (84 C4) being about a .32cd. Again this is from memory and might be wrong.
Seems like the 82-84 Trans Am was a .32cd unless it was equiped with the optional factory aero wheels or whatever they called them and then it dropped to .29cd which was the lowest in GM history at that point.
Seems like the 82-84 Trans Am was a .32cd unless it was equiped with the optional factory aero wheels or whatever they called them and then it dropped to .29cd which was the lowest in GM history at that point.
Safety Car
Joined: Dec 2008
Posts: 3,588
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From: North New Jersey
CD is an important number but remember that it can be misleading. If you look up the CD of race cars or super cars such as Lamborghini, Ferrari, and the new ZR1, the drag coefficient is relatively large. This is due to downforce which holds the car to the track. For the most part, the more downforce the greater the coefficient of drag. The key is to balance the two so that you are gripped real hard to the track and the car is slippery at the same time.
.33 seems about right for the C4
.33 seems about right for the C4
Drifting
Joined: Jun 2001
Posts: 1,704
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From: Mass Mass
From awhile back, you might find interesting 
Corvette Fever (May 2009) has an interesting article this month on Aerodynamics.
They took Corvettes, from each generation, and tested them in the AeroDyn wind tunnel (Mooresville, North Carolina).
http://www.a2wt.com
I don’t think I can “legally” post the whole article, but here are the graph results.
Data seams to be taken at 85 mph, and “Passengers” means they placed weight in the seats.
I put their CDA, Lift/Drag Ratio, and % Front Lift, into a spreadsheet and calculated values up to 200 mph.
Just did the base model coupes, with passengers.
Keep in mind this is just Aerodynamic Drag (from the data) and no rolling resistance.
And front and rear lift, again from their data.
Interesting stuff, if the data is believable?
The C5 has the lowest drag.
The C4 & C3 have the lowest rear Lift, even lower than the C6?
Look how high the C4 drag coeff is 0.371 ?
Anyway, hope this is interesting..
They took Corvettes, from each generation, and tested them in the AeroDyn wind tunnel (Mooresville, North Carolina).
http://www.a2wt.com
I don’t think I can “legally” post the whole article, but here are the graph results.
Data seams to be taken at 85 mph, and “Passengers” means they placed weight in the seats.
I put their CDA, Lift/Drag Ratio, and % Front Lift, into a spreadsheet and calculated values up to 200 mph.
Just did the base model coupes, with passengers.
Keep in mind this is just Aerodynamic Drag (from the data) and no rolling resistance.
And front and rear lift, again from their data.
Interesting stuff, if the data is believable?
The C5 has the lowest drag.
The C4 & C3 have the lowest rear Lift, even lower than the C6?
Look how high the C4 drag coeff is 0.371 ?
Anyway, hope this is interesting..
Drifting
Joined: Jun 2001
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From: Mass Mass
Burning Brakes
Joined: Aug 2010
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From: Placerville CA
That first chart is very interesting, SuperL98, and illustrates a point well known to motorcyclists even if they have never thought much about drag coefficients. It explains why a crotch rocket that can do 0-60 in 2.5 seconds and 0-100 in under six seconds can rarely reach 200mph (even on bikes which have their 188mph electronic speed limiters disabled). The cD of a the average motorcycle/rider combination is a tragic .50, and that adds up to a lot of drag as speed increases.
AFAIK, the best cD of a "production" vehicle was the P-51 Mustang, which came in at a very slick .15. Modern fighter planes like the F-15 are much worse, but they don't care. 50,000+ lbs. of thrust will make up for a lot of aerodynamic deficiencies.
AFAIK, the best cD of a "production" vehicle was the P-51 Mustang, which came in at a very slick .15. Modern fighter planes like the F-15 are much worse, but they don't care. 50,000+ lbs. of thrust will make up for a lot of aerodynamic deficiencies.
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Race Director
Joined: Sep 2001
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From: NEwhere Ohio
this is incredibly interesting and may help explain WHY C5's become unstable at speeds > 200 MPH. I recently read, on the c5 section, where a C5 became uncontrollable at 230+ MPH on the salt flats, and spun around a whole bunch of time. Though the owner modified the aerodynamics and was able to fix it the next time
C4's, with minor aerodynamic tweaks, like the callaway sledgehammer attained 254.176 MPH were still controllable at high speeds (though I remember john lignenfelter said that the car required 2 lanes of the track at that speed.)
Also, shows how all the brake scoops, etc. cause increased drag on the z06's.
C4's, with minor aerodynamic tweaks, like the callaway sledgehammer attained 254.176 MPH were still controllable at high speeds (though I remember john lignenfelter said that the car required 2 lanes of the track at that speed.)
Also, shows how all the brake scoops, etc. cause increased drag on the z06's.
Safety Car
Joined: Sep 2000
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From: Hinckley Ohio
I still struggle with understanding the new Toyota Camry Cd=.28 while C4 Corvette Cd=.34???
Burning Brakes
Joined: Aug 2010
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From: Placerville CA
I still struggle with understanding the new Toyota Camry Cd=.28 while C4 Corvette Cd=.34???
Safety Car
Joined: Sep 2010
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From: Indiana PA
There is one big thing you guys have forgotten about. Yes, newer Corvettes C5 and C6 have very good cD numbers. The C4 was ok in its day but not exceptional. This is only ONE part of the aerodynamic equation. You are forgetting that the Corvette has a very small frontal profile to the wind. So it may not be as aerodynamic as a Toyota Camry but I get it slips the air better as it has less frontal area.
Team Owner
Joined: Aug 2004
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From: Park City Utah
Burning Brakes
Joined: Aug 2010
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From: Placerville CA
Possibly, but not definitely. Did you see the Mythbusters where thye tested a Posrche 928 with the boddy on backward?
What was the Mythbusters conclusion?
Team Owner
Joined: Aug 2004
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From: Park City Utah
The car with the body reveresed went slower, coasted less far, and got worse gas milage. They myth was "busted" in their eyes. They even brought in another 928 to do side by side in case, and the forward bodied car was better (more efficient -according to them).
I hear what you're saying though. The car, backward is more like a tear drop, which is an aero dynamic shape. However, the sharply cut tail of the Corvette actually HELPS it's aero dynamic efficiency as compared to having a tapered rear (like the 928 does), as it makes a "clean break" for the air flow, instead of carrying the air around the back of the car. The flat back, as I understand it, carries a mass of air that has naturally forms a sort of tapered tail that is more aero than a bulbus, rounded rear end.
http://dsc.discovery.com/videos/myth...e-engineering/
I hear what you're saying though. The car, backward is more like a tear drop, which is an aero dynamic shape. However, the sharply cut tail of the Corvette actually HELPS it's aero dynamic efficiency as compared to having a tapered rear (like the 928 does), as it makes a "clean break" for the air flow, instead of carrying the air around the back of the car. The flat back, as I understand it, carries a mass of air that has naturally forms a sort of tapered tail that is more aero than a bulbus, rounded rear end.
http://dsc.discovery.com/videos/myth...e-engineering/
Last edited by Tom400CFI; Feb 2, 2011 at 06:58 PM.
Instructor
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From: Corvettes ruined my life. CA
The abrupt ending tail is called a Kamm tail after the person who discovered it
http://en.wikipedia.org/wiki/Kammback.
http://en.wikipedia.org/wiki/Kammback.
Racer
Joined: Sep 2021
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early .33/.34
91+ Cd 0.31 / 0.33 headlights up/retracted
frontal area ~1.86-1.88sqm
CdA 0.58 - 0.61 sqm
as a comparison: bmw z4 coupe - Cd 0.35
CdA 0.65 sqm
tesla model 3 former/highlander Cd 0.23-0.22
CdA 0.51 - 0.46 . very low Cd : small air vents, flat underbody, aerodynamic shape
often shapes look aerodynamic but in reality they are not, like this z4 example that you would expect to have a lower cdA unless the underbody plays a role that creates confusion.
the Cd basically tells you how aerodynamic is the 3d shape but the CdA takes into account the dimensions because a tiny toy car can have a large Cd but the drag force will be extremely small compared to a full size car. Moreover, often with sports cars, manufacturers will design the car with a lower profile that reduces the frontal area and lowers the cemter of gravity even if the Cd may go up a bit.
Anyway the C4 has an excelent CdA resulting in low drag at high speeds.
91+ Cd 0.31 / 0.33 headlights up/retracted
frontal area ~1.86-1.88sqm
CdA 0.58 - 0.61 sqm
as a comparison: bmw z4 coupe - Cd 0.35
CdA 0.65 sqm
tesla model 3 former/highlander Cd 0.23-0.22
CdA 0.51 - 0.46 . very low Cd : small air vents, flat underbody, aerodynamic shape
often shapes look aerodynamic but in reality they are not, like this z4 example that you would expect to have a lower cdA unless the underbody plays a role that creates confusion.
the Cd basically tells you how aerodynamic is the 3d shape but the CdA takes into account the dimensions because a tiny toy car can have a large Cd but the drag force will be extremely small compared to a full size car. Moreover, often with sports cars, manufacturers will design the car with a lower profile that reduces the frontal area and lowers the cemter of gravity even if the Cd may go up a bit.
Anyway the C4 has an excelent CdA resulting in low drag at high speeds.
