The CW-value, known also as drag coefficient and meaning how smoothly a car (in this case) passes through air, is a notion that has been part of the automobile world since at least a 100 years. In 1921 Edmund Rumpfler’s “Tropfenwagen” (drop car) became the first aerodynamically designed automobile, to be followed over the coming decades by cars like the Chrysler Airflow or the Tatra 77. I first become aware of it at a young age when my father bought a new Audi 80 B4 in the early 90’s that looked like a bar of soap, much like its larger brother did, the Audi 100. No doubt Audi had paid a lot of attention to wind resistance and if memory serves me right, the car had a CW-coefficient just below 0.3. That became a bit of a benchmark from then on that proved difficult to beat, with many cars managing 0.27-0.28, but few going below that. And then we got the horsepower race that we’ve seen over the last years, where less attention was paid to efficiency, as it could just be compensated with a more powerful engine.
The reason things like the CW-value are more important than ever is of course EV’s, as the fight for every km or range needs to go over as little resistance as possible, especially since every EV is penalized by its weight. Mercedes set a new CW-value record with the EQS (another soap-like car) at 0.20. And then just a few weeks ago, the Stuttgart brand also started showing their project car EQ XX to a wider audience, which has a hitherto unrivaled drag coefficient of only 0.17. That also means that equipped with a 100 KwH battery pack, it is the first EV to have a range of over 1000 km (735 miles). This week we’ll look at what makes the EQ XX an example of efficiency, and what it teaches us in a broader sense?
The EQ XX is a prototype car which if it goes into production one day as is rumored, it will not be in its current format. The prototype however looks rather nice, far nicer than any other EV Mercedes currently produces. It’s not reminiscent of Rumpfler’s drop car, but clearly the drop form has been the inspiration, especially over the extended tail. Looking at it from the front, some of the air inlets are also quite similar to a Porsche Taycan. But it takes more than that to get the CW-value of a car down to 0.17, so what has Mercedes done? Well, starting up front and next to the very visible are inlets and outlets, there are also active flaps under the front bumper that will vary their position depending on conditions and speed. There are of course special tires and wheels to reduce air resistance, and the long tail of the car ends with an active, extendable rear diffusor, which at speed reduces wind turbulence. A bit surprisingly the EQ XX doesn’t have side cameras but rather standard mirrors, but there’s a logic to this as well since apparently, the gains in reduced wind resistance of cameras is lost again by the power consumed by the screen that becomes necessary in the gauge cluster or the dash.
On the inside (and seen from videos and photos, given Mercedes for some reason didn’t invite me to the launch…), emphasis is on recyclable materials for one, and low weight on the other. Every metal surface is firstly not metal but rather 3-D printed recycled plastic, and secondly, as perforated as possible without it breaking into pieces. There’s a giant micro-LED display going across the whole dash which is said to consume much less power than a regular screen. There’s no sunroof since the roof of the car all the way down the rear window (which is thus also absent) is covered by solar panels. This is something I’ve never understood why you don’t see on more cars (with the exception of the Fisker Karma and perhaps 1-2 others I’ve forgotten about). Of course panels have become much more efficient and on the EQ XX, they are said to power many of the interior functions, producing somewhere around 4 Kwh in a (bright and sunny) day.
As impressive as the low wind resistance is no doubt that the fact that the EQ XX weighs in at only a1700 kg, very remarkable for an EV with such a large battery pack. Through that and its efficient shape, it only needs one 180 Kw engine while still managing a time to 100 km/h under seven seconds and a top speed limited to 140 km/h (87 mph). And as mentioned, it has a range that quite easily seems to trump 1000 km, with as much as 1200 km set as record on test drives. The official consumption number is 8.7 KwH per 100 km, which is roughly half of a normal, rather efficient EV. What does it sacrifice? Except for the very limited top speed, it doesn’t offer much room on the inside and as far as I’ve understood, no boot (there is also no frunk given the air outlets). Driving it seems to be an exercise in efficiency, as the dash will constantly show if you’re consuming or generating power, and also how much different functions in the car consume in real time. It also has wind sensors around the car with the wind taken into account for range estimates.
Summing it up, from an efficiency point of view, it’s as much the low weight as the wind resistance that impresses with the EQ XX. After all, a Mercedes EQS with only a slightly higher wind resistance at 0.20 is nowhere near 1000 km of range given it weighs at least 800 kg, or almost 50% more. And this is of course the efficiency lesson in an electric world – wind resistance is important, but reducing weight by reducing the comfort features of traditional cars is as crucial. This also highlights the inherent conflict in building heavy luxury cars or SUV’s as EV’s, and so when Mercedes tells us it will bring the G-Wagon in an electric version, you have to wonder where the efficiency thinking went.
It’s really positive to see that advances in materials (recycled plastics etc.) and production methods (especially 3D-printing) will bring weight gains to an increasing number of cars, and at some point when the realization kicks in that we are nowhere near the battery materials required to electrify the whole world (see here if you want more thoughts around that), this will come to benefit combustion cars and hybrids as well. I would guess that exterior design will then also become a bit more the focus again as was the case with Audi back in the 90’s. That’s a good thing, since the world can well do without any more G63’s or 3-ton EV’s. I therefor think we’re heading towards a future that will be of a mix of different drive trains, but if the more traditional of these become more efficient and thereby consume less fuel, that can only be a good thing, both for the wallet and the environment!