Yeah, GM's new EV BEV3/BT1 design language has turned their previously "for looks" designers into aerodynamic aestheticians, using each brand's classic design cues as a base. I recall a story where Bob Lutz had to really twist Gen 1 Volt-designer Bob Boniface's arm to get him to incorporate a small 2" spoiler on the Volt's rear. But that spoiler added 3 miles of range, which was a huge range win for a small design change when you only have a 10 kWh usable battery to play with. No arm-twisting now. I suspect it may be sort of a game....hiding aero Easter eggs that pay real dividends.
That Hummer EV 70 mph IEVs range test totally blew up my previously-accurate range model. I couldn't find anything in either the driving conditions or Tom's procedure that would have "gamed the range". It now has me putting Hummer images under a microscope to find their secret sauces.
Until I discover hard evidence of GM's baked-in aero magic, I've arbitrarily adjusted my previously-accurate range model to match the field-tested range + kWh used. Now I come up with:
Hummer EV: Cd = 0.40 (yeah!), assuming a 33 sq. ft frontal area. I'm suspecting that Volt-like 2" rear spoiler on the cab's top, slight downward arcing roof taper towards the bed, tail-gate spoiler, and those angular side sail-gussets linking the cab and bed do more than we realized to minimize bed-induced vortices and reduce drag. Also, I suspect things going on everywhere else that I just haven't picked up yet.
Regarding Rivian: There is now substantial evidence both through outside-CFD-modeling and real-word range testing that the Rivian's Cd is in the range of 0.31-0.32. Rivian's engineers and designers did a world-class aero design job, full stop. Frontal area = 30 sq. ft.
The Silverado EV has a different design language, with more sharp edges than Rivian's more-rounded features, but it incorporates essentially all of Rivian's aero tricks + includes the Hummer side cab/bed sails, and if you look closely, you'll see the bed's side panel tops are not horizontal, they rise up higher at the side-sail connection and then gently taper down to the tail gate. That likely maintains attached side-air-flow better than Rivian's horizontal bed rails. But I did notice Rivian uses the same advanced-aero combined rear spoiler/air curtain as the Lyriq's at the cab's back, while the Silverado doe not. The Lyriq shows that GM is familiar with the concept. Perhaps because the Silverado's bed is longer and cab roof tapers down at a steeper angle than the Rivian's, GM's designers found the air curtain feature didn't provide any benefit, or perhaps it was just a small aero/design compromise.
I'm figuring the Silverado likely about matches the Rivian Cd to Cd, but has a 5%-10% larger frontal area, so overall aero drag road load is still higher. I'm now guestimating about 450 miles at 70 mph fixed speed. Cd = 0.32 @ 32 sq. ft frontal area.
Ford is not far behind either the Rivian or Silverado. Except for missing the cab rear spoiler and the Silverado's cab/bed side sail panel, their aero designers also checked all the boxes.
My range model, using 0.36 Cd and 32 sq. ft. frontal area, came up with 271 miles at 70 mph. That closely matches Tom's IEVs 70 mph range test @ 271 miles, performed in near perfect driving conditions.
@Tom E-Tron: I know you and many others are mesmerized by Lucid's drive train, and especially Rawlinson's recent presentation, and want to directly compare it to GM's ultium drive units. But as an engineer who has lately been deeply-steeped into EV drive-train/battery design, what I saw in Peter's video was two parts solid/creative engineering, two parts well-crafted showmanship, and a hint of PT Barnum. Lucid truly did create a world-class drive unit, mechanically-miniaturized and light-weight, perfect for besting it's competitors' luxury platforms. But that is a Rolex design. Peter even described the miniaturized in-shaft differential as a "Swiss watch". But did not mention the Swiss watch cost.
Rolex is different than Timex, but the watch makers/engineers within either brand have the same basic skill sets. Just targeting their skills to radically-different markets. The Ultium platform's centroid is not Rolex. It is Timex. It is $30K Equinox and $40K Silverado WT. It is EVs For Everyone. Not EVs For Saudi Princes. I strongly suspect GM is reserving their Princely-level EV engineering for the soon-to-come Celestiq. We'll likely see a whole other technological level inside that vehicle. Michigan-based hand-crafted Rolex's, straight out of the Warren Global Technical Center.
