Regular cars with really good aero.

I know that everyone automatically assumes that the Dodge Charger Daytona and Plymouth Road Runner Superbird have great aerodynamics, but talk to people who race them in land speed racing these days and they tell you that they are actually pretty terrible as they sit. A ton of lift on the front and a lot of frontal surface area.  Lee Sicilio says that the rear wing doesn't matter much from a downforce perspective either, although the vertical elements add a ton of directional stability.

Robbie said:

Cd by itself does not equal low drag....

just to add to this, stole this from a website:

Calculating drag

This equation is used to calculate the drag of an object:

FD = ½CD AρV2

• FD is the drag force.
• CD is the drag coefficient (a number that shows how streamlined a shape is). Lower CDnumbers show that there is less drag, for example:
  • circular cylinder – CD = 1.2
  • square cylinder – CD = 2.0 (sharp edges are not good)
  • oval cylinder – CD = 0.6 (rounded edges are good)
  • wing shape – CD = 0.1
• A is the frontal area of the object (measured in square metres).
• ρ is the density of air (about 1.2 kilograms per cubic metre).
• V is the speed the object is travelling at (measured in metres per second – m/s).

so, if you ignore air density and speed for a moment, it's not JUST CD, but it's CD x frontal area that affects aero drag.  
therefore, you can have two vehicles with the same CD, but one with a very large frontal area and one with a very small frontal area (say maybe some tiny car vs a semi truck that somehow had the same CD) and they would have drastically different drag forces acting against them when moving at the same speed through the same density of air.  

correct me if I'm missing anything of course :)  

I also read someplace (I should really fact check this), that going from something like .25 to .29 CD, you might lose something like 1/2 mpg at normal highway speeds, and dropping down to .21 CD (probably depends on the size of the vehicle and many other things), you might gain 1/2 to 1 mpg.

So, from what I understood, moving CD up or down a few 100ths is going to have a really really small effect on MPGs unless perhaps you are a trucking company where every penny counts.  For us average types, fuel savings will probably be pretty tiny.

but again, I haven't checked all the math myself, so this could be off by a bit.

In reply to lastsnare :

Your analysis is overall correct. CD and A are the primary values to look at when comparing different cars.

We could run the number for the CD changes you mentioned and verify the change in power required and then estimate the fuel consumption rate change.

Since I spend a lot of time in wind tunnels working on race cars, I have to laugh at the reliance on the first two digits of the CD values. For the race cars we generally look to the third digit, while the production groups are looking at the 4th and 5th digits. The production groups have to answer to the CAFE standards and budget guys, so any measurable reduction in CD is a good thing, unless it costs too much!

The article that JG did a year+ back on the effect of tire changes affecting total drag had a very large influence. If I recall the stock tires on the car gave a drag force of 60ish pounds while the race tires increased that to ~120ish pounds. Not aero but the things we do to cars may have as big or bigger impacts on the total drag of the car.

I think it was Hot Rod Magazine that not too long ago wrote about aero testing done on a Superbird and how the wing could be adjusted to provide actual downforce.  It was at something like 40 degrees nose down to do so, looked crazy in its mounts, and created a ton of drag in the process.  

I wonder if lowering the front noticeably would instead improve the frontal life and give some downforce at the same time, or at least reduce rear lift.  

Perhaps basing the 'bird on the A-body cars would have maximized the work done in the windtunnel due to less length and width of the cars.  There were 426 Hemi and 440 Wedge Darts from Chrysler so the engines were already there.

ooh, here's a calculator thingy:

http://ecomodder.com/forum/tool-aero-rolling-resistance.php

if it's correct, when I put different numbers in for just the CD (say .25 ... .30 ... .35 ), and look at the differences at 60mph,

perhaps it does actually make a noticeable difference

My 1999 Intrepid lists as a .299 and a frontal area of 2.2200m(squared) 

Concreting the idea of it seems like a good 'on paper' car

Some unregular stuff but fun stuff from the web-

1934 T77 0.212

1939 Schlörwagen prototype  0.186

Citroen SM  at 0.26

Aptera mk0 prototype 0.11

VW 1L prototype 0.15

Ok some regular stuff..

2000 dodge caravan 0.35

Previa  0.33

Jeep TJ  0.58

And yes "duh frontal area" comment +1...

pres589 said:

I think it was Hot Rod Magazine that not too long ago wrote about aero testing done on a Superbird and how the wing could be adjusted to provide actual downforce.  It was at something like 40 degrees nose down to do so, looked crazy in its mounts, and created a ton of drag in the process.  

I wonder if lowering the front noticeably would instead improve the frontal life and give some downforce at the same time, or at least reduce rear lift.  

Perhaps basing the 'bird on the A-body cars would have maximized the work done in the windtunnel due to less length and width of the cars.  There were 426 Hemi and 440 Wedge Darts from Chrysler so the engines were already there.

I believe the fix for the front lift was that you had to mount a front air chin spoiler way out near the front of the beak, instead of where it it is located stock. By all accounts, the engineers/aerodynamicists knew this but couldn't get the stylists to sign off on it, because the stylists said it made the car look even weirder and it was going to be a tough sell as is.

Making an aero package for the A-body might have worked better, but they wouldn't be NASCAR legal, because the A-body was a compact and NASCAR required an intermediate.