Aerowhatt, I am saddened by the vehemence in your remarks because, like the man in the movie said, "what we have here is a failure to communicate".
Here's where we agree: on any downhill, be it a 5000-ft mountain drop or the backside of a highway overpass, judiciously alternating between N and D (or even E and B to avoid going too fast) will result in optimizing the car's distance traveled/charge.
You and I both do this, and we'll see who's first to wear out the shift lever.
On downhills, neither of us advocates leaving the car in "gear" continuously, be it D or E or B, and attempting to "feather" the gauge at the "zero-energy" point. I personally find it impossible to find and hold that "zero-energy" spot (somewhere between green and blue on our power meter).
You have aptly demonstrated this by showing the CaniOn data for the five-mile stretch, the metric of interest being miles/kWh, showing the differences among D-N, D, E, and B. I note that your average speed on these downhills is around 60mph, which is what I also usually hold the car to unless surrounding traffic dictates otherwise.
Once again,
we are in complete agreement on the coasting technique, each of us having espoused and advocated it in numerous posts on this website for years.
So, what's all the fuss about?
What I've unsuccessfully been trying to convey is that we have an even more subtle subset within this advocacy discussion.
Specifically, on a steep downhill (say, >6% grade) where we can alternate between N and the other settings to maintain a constant speed during this downhill, all I'm saying is that we will get a better result by maintaining a lower speed. By "better result" I mean a lower Wh/mi or Wh/km or higher mi/kWh or km/kWh for that particular stretch of road.
My basis for this argument is that aerodynamic drag at the lower speed will be lower, thus allowing us to stuff a little more energy back in the battery at the lower speed than at the higher speed (since the car has a higher retarding force at the higher speed).
In an attempt to demonstrate this I tried to set up an extreme case whereby one car merely coasts while the other regens continuously and I thought that coasting would show no change in SoC whereas regenning would show an increase in the SoC at the bottom of the hill. Notably, as shown by your arguments and my own recent experience, this scenario is proving to be unrealistic - I haven't found a hill long enough and deserted enough around here to demonstrate this. I am sorry that this extreme example attempt on my part became misconstrued.
So, where are we?
Aerowhatt has shown data comparing the N-D (and E and B?) technique vs. leaving the car in D or B or E, at the same constant speed.
I would like to do the same, but using the N-D-E-B technique comparing two different constant speeds: say, 70mph vs. 50mph.
In real life, during the last 2-1/2 years and 60,000 miles that I've criss-crossed this country and made numerous West Coast trips in the Tesla I have often had the opportunity when facing a 6%, 7%, or even 9% downhill to select the cruise control speed at which to go down those grades and have actually slowed down a few times when I was running a bit low. Did it do any good? - I dunno. Hmmm, now that I think about it, I could do a controlled test in the Tesla even though it has a much lower Cd than the i-MiEV and the result might just be measurable, and it just might work... now, all I have to do is convince my wife that after we've gone down the hill that we're going to go back up and do it all over again!
To close this, once again, Aerowhatt - you and I are in violent agreement that coasting is superior to leaving the car "in gear". I'm simply trying to say that going downhill slower is ever-so-slightly better.
