COEFFICIENT OF DRAG - LotusTalk - The Lotus Cars Community
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post #1 of 92 (permalink) Old 05-20-2007, 07:37 PM Thread Starter
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Question COEFFICIENT OF DRAG

When GM introduced the EV1, it claimed that the EV had a lower coefficient of drag than the Corvette. Does anyone know what the coefficient of drag is for the Elise compared to the EV and/or Corvette?

It looks to me that the Elise has a lower cross section than either the Corvette or EV. That would seem to indicate a lower coefficient of drag, but I recall that the rear end of the Elise has some aerodynamic issues.
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post #2 of 92 (permalink) Old 05-20-2007, 07:49 PM
 
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It's pretty misserable unfortunately. On the Lotus site, the Exige is listed at something like .437. The topic of putting Elise in the same touring class as the Vette was talked about for a year on the SCCA site. The Vette always comes out on top for speed. On a long track even high hp Lotuses have to watch slippery cars go by. I'm not into aerodynamics but it seems there could be a few chages to get the air over or around more easily. All that area under the headlights is rather blunt and has to go around the sides suddenly. The large mouth is geat for radiator cooling but the car pays a price for that too.
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post #3 of 92 (permalink) Old 05-20-2007, 08:07 PM
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Quote:
Originally Posted by Patrick
It looks to me that the Elise has a lower cross section than either the Corvette or EV. That would seem to indicate a lower coefficient of drag, but I recall that the rear end of the Elise has some aerodynamic issues.
The coefficient of drag is independent of cross section. One metric that corresponds more closely with total drag is "drag area" which is the product of Cd and cross section. By that measure the Elise is as good or better than a number of other sports cars.

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post #4 of 92 (permalink) Old 05-20-2007, 08:14 PM
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Quote:
Originally Posted by Patrick
When GM introduced the EV1, it claimed that the EV had a lower coefficient of drag than the Corvette. Does anyone know what the coefficient of drag is for the Elise compared to the EV and/or Corvette?
Here's a list of representative drag areas:http://en.wikipedia.org/wiki/Drag_co...in_automobiles
According to that list, the Elise and Corvette have similar drag areas.

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post #5 of 92 (permalink) Old 05-20-2007, 08:14 PM
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0.36 for the S2 Elise according to the Walton Elise book

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post #6 of 92 (permalink) Old 05-20-2007, 08:25 PM
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S2 Elise Cd 0.407, A 1.6 m2, CdA 0.651 (figures from Lotus).

The first point is that while Cd is a good measure for effects of changes made to one vehicle, it is not that useful to compare Cd between vehicles because of the variance in cross sector. Thus now the trend is to use CdA (CD x Area).

The second, and most important point, is that the Cd figures quoted by manufacturers are claimed figures. There is no verification or independent test for them. Do not believe the figures that you see - the actual numbers can be much, much higher than what is quoted. Having said that, the Lotus numbers are probably accurate. Just don't use them in comparison with anything else.
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post #7 of 92 (permalink) Old 05-20-2007, 08:32 PM
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I thought that there is Cd and Cx.
One is coefficient and one is total drag.
I have a large but very low drag car and at higher speeds many cars that are virtually identical otherwise, have no chance.
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post #8 of 92 (permalink) Old 05-21-2007, 04:17 AM
 
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It is ironic but sports car generally has bad aerodynamics.
The worst is round car like TT and bug. The aerodynamics of TT was so bad, its got a rear wing shortly after to make the car stable but the wing itself is a drag.
I imagine Elise is one of the worst as well, considering how much curves it has around the side of the car. Lotus knows it and they made the side flat on the TwoEleven track car for the perfomance purpose.

The best ones are probably Prius and Insight.
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post #9 of 92 (permalink) Old 05-21-2007, 04:45 AM
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Quote:
Originally Posted by gogogo
It is ironic but sports car generally has bad aerodynamics.
The worst is round car like TT and bug. The aerodynamics of TT was so bad, its got a rear wing shortly after to make the car stable but the wing itself is a drag.
I imagine Elise is one of the worst as well, considering how much curves it has around the side of the car. Lotus knows it and they made the side flat on the TwoEleven track car for the perfomance purpose.

The best ones are probably Prius and Insight.
Good point! But luckily for us Lotus also figured that looks outweighed high speed performance!
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post #10 of 92 (permalink) Old 05-21-2007, 04:49 AM
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Originally Posted by Aedo
Good point! But luckily for us Lotus also figured that looks outweighed high speed performance!

Seriously.....I'd rather take a bubble bath with my Dad than drive a Corvette, spending my life suffocating in that vinyl interior. Good thing aero doesn't matter so much in the twisties.
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post #11 of 92 (permalink) Old 05-21-2007, 07:19 AM
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Originally Posted by fingolfin
Seriously.....I'd rather take a bubble bath with my Dad than drive a Corvette, spending my life suffocating in that vinyl interior. Good thing aero doesn't matter so much in the twisties.
I haven't met your Dad, but I still doubt this.
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post #12 of 92 (permalink) Old 05-21-2007, 07:30 AM
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The 1997-2004 Vettes are .29, 2005-now are .28.

http://www.vetteweb.com/features/040...t_corvette_c6/

http://www.corvettemuseum.com/specs/2005/

The slippery designs of these cars is one of the reasons they get nearly 30MPG on the freeway. That and the wretched 6th gear.
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post #13 of 92 (permalink) Old 05-21-2007, 07:45 AM
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Quote:
Originally Posted by gogogo
It is ironic but sports car generally has bad aerodynamics.
The worst is round car like TT and bug. The aerodynamics of TT was so bad, its got a rear wing shortly after to make the car stable but the wing itself is a drag.
I imagine Elise is one of the worst as well, considering how much curves it has around the side of the car. Lotus knows it and they made the side flat on the TwoEleven track car for the perfomance purpose.

The best ones are probably Prius and Insight.
No. You are talking about two different concepts simultaneously. Drag and lift. The TT has very low drag. The round egg shape is very aerodynamic from a standpoint of low drag. However, it is lift that causes instability at high speeds. The prius and insight are probably very unstable at high speeds because they doubtfully have anything in their design to generate downforce. The reason you don't hear about them as being unstable is because no one drives them at 100 mph.

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post #14 of 92 (permalink) Old 05-21-2007, 08:59 AM
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IIRC the EV1 had a Cd around 0.19.
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post #15 of 92 (permalink) Old 05-21-2007, 10:04 AM
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the miserable body drag (styling), + the modest (yet more than most road cars) downforce adds up to lots of drag - although as mentioned it is a punching a small hole (its a small car) in the air. anyways - its not a wind tunnel body work car thats for sure!! gets the job done under 100mph - after that your doomed, although your looking really good going slow

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post #16 of 92 (permalink) Old 05-21-2007, 12:48 PM
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Actually the Elise aerodynamically is fairly good. The only major fault is the rear window / engine tray - which generates lift and drag as it is. Of course, the Exige shape fixes this.

The Elise was put in a wind tunnel during development, and generates downforce both front and rear. Very few production cars generate downforce - the only ones that spring to mind are the F40, F50, Enzo, Carrera GT, Veyron, Mclaren F1, Koenigsegg, S7, GT3(?) - none of which I really consider production cars apart from the GT3.
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post #17 of 92 (permalink) Old 05-21-2007, 01:12 PM
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The 100lbs of downforce at 100mph for the Exige is no more draggy that any number of cars that produce 100lbs or more of lift at the same speed. It's just a lumpy, scoopy shape people.

Now THIS is how you go 280mph on 200hp or less:


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post #18 of 92 (permalink) Old 05-21-2007, 02:17 PM
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The short length of the car is probably a major factor in limiting drag.
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post #19 of 92 (permalink) Old 05-21-2007, 02:40 PM
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A long car has more frictional drag but generally less pressure drag than a shorter car, and so is easier to make aerodynamic. The Elise does well for its length. I'll giving up.
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post #20 of 92 (permalink) Old 05-21-2007, 02:52 PM
 
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Im a car designer and engineers always tell me to make the rear shaper for better Cd. They want the air to follow the side and top but they want the air to seperate at the end becauseround shape creates negative pressure behind. Basically an egg with chopped off rear is the best, like a bullet.
Ok, maybe my TT point was a bad example but Prius, Insight has excellent Cd. Figures.
Good thing about Elise is that the bottom is completely flat and that should help a lot.

Compared to Elise? Does Exige have better CD? Im curious.
Its got a fastback but Its got a wing and fatter tires...

Quote:
Originally Posted by Conan
No. You are talking about two different concepts simultaneously. Drag and lift. The TT has very low drag. The round egg shape is very aerodynamic from a standpoint of low drag. However, it is lift that causes instability at high speeds. The prius and insight are probably very unstable at high speeds because they doubtfully have anything in their design to generate downforce. The reason you don't hear about them as being unstable is because no one drives them at 100 mph.
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