Teardrops and wind tunnels: A look at the world’s most aerodynamic cars

Inspired by VW's ARVW concept, we look at the cars with tiny drag coefficients.

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[Jim Z]

"lake" wheel covers used to be a common sight back in the early days of people making speed runs on the Bonneville Salt Flats.

 

[Jim Z]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

'cos chances are they don't? This sounds like the same kind of bunk that gets promoted as "fuel saving devices" for ICE vehicles. Nonsense like fuel line magnets, intake air vortex generators, blah blah. they rely heavily on confirmation bias. people install these devices, then subconsciously alter their driving style to be more "gentle" thus fooling themselves into believing the gadget is what improved their gas mileage.

believe me, if Tesla could eke out another 6% with some simple bolt-on devices, they'd be on every car they build. 6% is the kind of gain any car company would spend money to get. the vast majority of the time when any aftermarket bolt on device does make a noticeable difference, it's only in specific situations and often degrades things in other situations.

 

[Jim Z]

As a Model 3 owner, I've wondered why the aftermarket front and rear spoilers aren't the stock designs, especially if they can offer ~6% efficiency gains!

'cos chances are they don't? This sounds like the same kind of bunk that gets promoted as "fuel saving devices" for ICE vehicles. Nonsense like fuel line magnets, intake air vortex generators, blah blah. they rely heavily on confirmation bias. people install these devices, then subconsciously alter their driving style to be more "gentle" thus fooling themselves into believing the gadget is what improved their gas mileage.

Sometimes it is possible! My company remapped all our vans, and put stickers on the back saying they had 25% less emissions. This seemed unlikely, but having driven thousands of miles before and after, I think it's true. I used to get 350-400 miles from a tank of diesel, now I get 450-500 - 25% more range tracks with 25% less emissions.

It doesn't feel any less powerful, but the power is compressed into a narrower band requiring more careful gear choice (like most European vehicles, it's a stick shift). It didn't take me long to get used to it, and now I'm baffled as to why the manufacturer didn't do it - efficiency sells!

horseshit. 25% increase in fuel economy with just a reflash? That doesn't even pass the sniff test.

 

[Jim Z]

There was also the Oldsmobile Aerotech

https://en.wikipedia.org/wiki/Oldsmobile_Aerotech

what's funny is that part of the Aerotech's purpose was to demonstrate how great the new "Quad 4" 16 valve engine was. But as was typical for Old GM, the engine that entered production was about 85% finished. it was impressively powerful for the time (180 hp w/o turbocharging) but had all the refinement of a Soviet tractor. The lack of counterbalance shafts made the noise and vibration unpleasant at best.

Just like things like the Fiero, Olds diesel V8, HT4100, and so on, by the time they got the Quad 4 right (added balance shafts, redesigned the head for improved NVH) its name was mud and ended up being discontinued.

 

[Jim Z]

How in the heck are those snub-nosed, angular BMW and Mercedes sedans getting similar Cd numbers to the other smoothly-curved vehicles with sloping profiles?

Long ago, I read Dr. Hoerner's technical book, Fluid-Dynamic Drag. In it, he showed frontal contours (radii) needed to produce nose sections with no separated flow and thus low frontal drag. It turns out that the radius is quite small for even Autobahn speeds. So, you can have a snub-nose with no separation effects near the nose. (If you want to keep total drag low, you have to carefully taper the back half of the car to avoid flowfield separation and thus a large base drag.)

You'll be telling us next that SUVs have quite good drag characteristics.

aerodynamics isn't always intuitive just by looking at something. When the new for 2009 Ram pickup was unveiled, in interviews Ralph Gilles pointed out that canting the grille forward a bit actually improved the trucks aero performance over the outgoing model's near vertical grille.

it also helped that the truck was a damn sight better looking in every way than the "Daimler-ized" googly-eye 2006-2008 truck.

 

[Jim Z]

I am kind of surprised the pictured Mercedes CLA 180 could pull a Cd of 0.22 considering the pretty square and blunt looking front end.

They must have made up for it in ways that aren't apparent.

like the Ram example above, aero can be counterintuitive on the surface.

similar to when everyone bitched up a storm because the production Chevy Volt looked almost nothing like the concept:

Bob Lutz said the problem with the concept is that it it would be more aerodynamic if it was driven in reverse. Thus why the production Volt looked a ton more "Prius-y."