You forgot to append 'driving slowly' to your sentence.
It's not necessary. As you often quote, a mag turned on the AC to 72°F (frosty, eh? That draws 3-4 kW on our cars) and locked the cruise at 75 mph in California, which doesn't have a lot of flat areas, and recorded 190 miles of range in hot weather.
If the aero was tragically poor, I'd think would lose a lot more than that. 217 vs 190 with the AC blasting at laboratory temperatures over hilly terrain?
Let's look at the closest thing we can get to apples to apples:
2017 Volt EREV final eng'g 2015.
.28 Cd (Tested by Car & Driver)
Height 56.4"
Width 71.2"
Height x Width
4015 sqin
Weight 35xx lbs, tires 215/50-17 LRRs.
2017 Bolt EV final eng'g 2016.
.308 Cd (according to latest data reported by GM, but don't trust it, you'll see why shortly)
Height 62.8"
Width 69.5"
Height x Width
4385 sq in
Weight 35xx lbs, tires 215/50-17 LRRs.
So the Bolt is about 9% more cross section give or take. Probably more due to the more boxy cross-section.
And it has 10% greater Cd, or close to
19% more aerodynamic drag.
The Bolt has a EPA hwy of 217 and city of 255 mi which is a
15% highway test hit.
The Volt has a EPA hwy of 49 and city of 57 mi which is a
14% high test hit.
Can you see the problem? Higher speeds with should favor the car with 19% better aero. But it doesn't have much effect.
65 mph to 75 mph for a car like a Bolt, should show 32% more power required. 217 EPA hwy / 190 C&D at 75mph is only 14%. Why doesn't it line up? Only two possibilities for such a large error. Either the Bolt EV's technology jumped wildly in 1 year, or the numbers Chevrolet reported to the EPA were too low.