How much fuel is wasted to bad aero design ?

[Cd]

For those of you good in math on this forum, I was just curious how many gallons / liters of fuel could be saved each year if auto makers simply incorporated an extra crease or two into their bodywork to bring the Cd down into the mid twenties versus the usual .31 Cd most cars have now a days.

From Wikipedia :

" According to the US Bureau of Transit Statistics for 2008 there are 255,917,664 registered passenger vehicles. Of these, 137,079,843 were classified as automobiles, while 101,234,849 were classified as "Other 2 axle, 4 tire vehicles," presumably SUVs and pick-up trucks. Yet another 6,790,882 were classified as vehicles with 2 axles and 6 tires and 2,215,856 were classified as "Truck, combination." There were approximately 7,752,926 motorcycles in the US in 2008. "

Lets say that 100,000,000 cars listed above had an average Cd of .35 and an average F.E. of 25 MPG.
Then lets compare the same cars, but this time dropping the Cd down to .25 , with the increase in fuel economy from less aerodynamic drag, how much fuel would be saved if each vehicle traveled 100,000 miles ?

How much fuel could be saved if the Cd was dropped to .25 and the F.E. brought up to 35 mpg like the proposed new regulations ?

We all know that to get good aerodynamics, the ideal car would look like an oversize roach ( example - the GM Sunraycer ), however I am continually surprised to see ordinary 'boxy' looking cars getting excellent drag numbers.
An excellent example being the recent post from lunarhighway regarding the Mercedes B class hatchback.
new mercedes b class 0.24 Cd



After looking at this car from all angles, it really makes one wonder why that all the rest of the cars out there have such 'high' Cd numbers in the .31 range.

Nearly every hatchback car sold in the U.S. today has a Cd of .31 It seems to be the standard.

As a reminder of cars that are sleek, but look ordinary, the Lexus LS430 had a Cd of .25, which matches that of the first Insight and current Prius.



When I look at the design of the B class and also think back on the design of the Lexus LS430, it seems obvious to me that cars have a huge amount of freedom for designers to make cars that look exciting and different.

Just because a car is streamlined does NOT mean it has to look like every other aerodynamic car .

[Frank Lee]

Yeah, with all the millions they've spent on wind tunnels and people to run them, you'd think they'd have more to show for it.

[jakobnev]

To answer the simple question about increasing mileage from 25 to 35:

100 000 * 100 000 000 * ((1 / 25) - (1 / 35)) = 1.14285714 × 10^11

So, many many many gallons.

[euromodder]

It's worse than that.
US average FE is 22 mpg or thereabout.

[Cd]

Back to that original question, how much fuel ( and tons of carbon emissions ) could be saved if car makers simply added an extra crease or two to bring their Cd figures down into the mid twenties ?

Lets just forget changing the CAFE standard complexities and think about about how much is wasted simply to bad design. As we can clearly see by looking at the above images, low drag cars can look quite ordinary.
The MB B class looks much like any other hatchback on the road, yet has a Cd count of at least 7 counts lower. The same with the Lexus. Next time you see one of these cars in the parking lot, stop to take a look at it. They look entirely average. Even the wheel spats seem undersize, yet the car is around five counts better than most cars out there.
So it seems that with just a little bit of tweaking, we could all be driving cars ( and some trucks ! ) with Cd figures in the mid twenties.

[jakobnev]

Originally Posted by Frank Lee

Yeah, with all the millions they've spent on wind tunnels and people to run them, you'd think they'd have more to show for it.

I think the could have gotten better results by diverting some of that money towards shotguns and a few "motivational" visits to the marketing department.