New world's best Cd for a current production car: 0.24, Mercedes 2009 E-Class coupe

[MetroMPG]

http://www.youtube.com/watch?v=1UWdvZCYKGA

[MetroMPG]

I noticed one characteristic at the rear of the Merc that's shared by the Honda Insight (gen 1) and even the latest gen Metros.

In each of those cars, the "haunch" over the rear wheel isn't only a styling feature.

It lets them place the wheel at the "outside" of the lower bodywork, while tapering the greenhouse above it significantly more. That line serves as the transition from the plane of the outside of the wheel to the greenhouse boat-tailing.

Insight gen 1's is most pronounced:



Of course they could all have done a smoth transition as well and eliminated the "line".

[lunarhighway]

i noticed that too, although i didn't make the insight link... i think with the increasing wider track of cars perhaps we're finally moveing back to those wheelfairings on 30's cars... who also had real boattails.... kind of like the aptera does in an extreme way

since it's real world Cd is about the same as the calibra i thought i'd overlay the profiles and lo and behold, an almost perfact match... because Cd-wise the new insignia is also somewhat in the same league i'd thought i'd trow it in the mix,and although it didn't match quite as nice, it's very close and in line drawing it actually looks surprisingly similar to the merc.... especially since unlike the other two it's stricly not a coupé but the regular 4 door sedan!



anyway, seems like generally this is a pretty good shape than!

[Unforgiven]

Ahh, wonderful MB ... too bad it has taken them so long to get that Blue diesel over here and that so many Americans (as a whole) are idiots when it comes to the advantages of diesel over gasoline... ah well.

[MetroMPG]

Here's the first gen Insight (Cd .25) and the new E-Class:



I scaled the Insight to the same height as the E-Class, and tried to line them up so the peak of each car's roof are at the same point.

Note the backlight angle on the hatchback essentially points at the end of the decklid of the Merc, an example of the "effective" angle of the back of a 3-box car being the line between the trailing edge of the roof and the end of the decklid.

[Bearleener]

Here they are smoothing the underbody panels:
Mercedes E-Klasse: Sicher und getarnt - Bilder - Fahrerassistenzsysteme - FOCUS Online

Yeah, that's well-disguised. Good job!

In terms of the fuel economy keep in mind that, unlike the new EPA figures, the European "EPA" driving cycle is unrealistic because it's a synthetic, non-road-data-based test that in recent years has been delivering overly optimistic figures compared to the real world to the tune of about 1 L/100km, which means the Benz's 5.3 may be more like 6.3 L/100km (37 mpg) in the real world, but that's not too shabby, either.

The European "EPA" cycle has relatively few, low-speed simulated highway passages, which explains why the Europeans hadn't been doing as much as they could aerodynamically.

On a German page they mentioned some of the efficiency changes:
> Better engine
> For the sedan (Cd= 0.25): 4% better Cd compared to previous model = 0.25 L/100km less fuel consumption at 130 km/h
> "Venetian blind" controlled air vent behind the grill a la BMW
> 17% less rolling resistance tires
> Efficient controllers for accessories (alternator, fuel pump, A/C compressor, power steering)
> Stop/start function

(By the way here are some nice historic wind tunnel photos:
Die Geschichte der Aerodynamik - Vom Winde verweht - Klassik - autobild.de
)

[Cd]

Here are some images of the CLS 500. The car appears to have a more tapered rear end than the current car, yet has a much higher .30 / .31 Cd.

I don't understand what could make the cars so much different.

[MetroMPG]

Do you have a copy of Hucho's book yet, Cd? He'd say "detail optimization".

[Cd]

Originally Posted by MetroMPG

Do you have a copy of Hucho's book yet, Cd? He'd say "detail optimization".

I'm to cheap to fork over the hundred bucks or so - besides I'm not sure my brain can understand that stuff. ( Brain running at half a Mhz )

Can you ( or someone else ) give an explaination of what " detail optimization " is ?
I'm guessing that 'detail optimization' would mean 'tweaking' the car in a wind tunnel.
If so, it seems as if M.B. would want to do this to all of their cars. That's 5 - 6 counts that they knocked off simply by 'detail optimization' vesus the previous car - which actually looks sleeker.

I'm actually really confused at how high that the Cd figure is on the CLS500.
I have read both .30 and .31 as the Cd for the car, despite having what looks like all the right angles.
.31 is the same as our Hondas !

It's surprising to me how the slightest bump on a cars surface can have such a dramatic effect on its Cd.

Steering the topic back to the new car, I'm glad that M.B. has done away with the Mickey Mouse headlight design.

[MetroMPG]

You should splurge for the book. You'll get more quality time out of it than you will spending an equivalent amount of $ on movies! Every once in a while one comes up used on eBay for a bit less.

Yes, detail optimization is basically "tweaking", as you said. Optimizing cooling, wheels, mirrors, glass & window/door seals, leading & trailing edges, slight taper, etc.

The shape alone doesn't mean much if the details are all wrong. You could easily take a 1st gen Insight and put its .25 Cd past .30 with wider wheels, blender rims, a badly designed front fascia, no rear skirts, unoptimized underbody, too much grille, etc.