Yesterday, I took a drive from Pasadena, CA up to Mt. Baldy, partially as a recreational outing, partially to test the Model S's mountain performance. My wife kept notes so we could see how the charge status would be affected.
Firstly, let me say that mountain driving with the Model S is every bit as much fun as you'd expect. Cornering is marvelous, uphill passing pure entertainment, and - as it turns out - range is not as severely affected as at least I had expected.
Miles are rounded, so there are small inaccuracies, but nothing of consequence.
The first leg was 24 miles of freeway along the foothills, with little relative elevation change (+1000 ft), cruise at 74mph, which averaged out to 65 mph including local driving. The rated range decreased from 187 to 155, 32 miles range loss for the 24 miles driven - the higher speed took its toll, as I expected. I averaged about 350 or 360 wH/mile.
The climb to Mt Baldy Village is a 9 mile drive to about 4200 ft., so we gained 2200 ft in elevation. The rated range went from 155 to 129, which gives us a "climbing penalty" of slightly below 8 miles of range per 1000 ft gained. (155-9=146, 146-129=17, 17/2.2 = 7.7miles/1000ft) The average speed of the climb to that point was about 35-40 mph.
Then came a steep climb up to the bottom of the ski lifts, from 4200 ft to 6500 ft in just under 5 miles. That dropped the rated range from 129 to 110. The "climb penalty" was less this time (6.1 miles/1000ft), perhaps because the average speed was much lower (24 mph).
Now came the surprising part: I knew the car re-generates power on the way down, but I was curious to find out how much. So I drove down without using the brakes except for a couple of little taps. After the the 14 mile descent the rated range had increased from 110 to 124!
So, the average "climb penalty" on the way up was about -6.3 miles/1000 ft, the average descent gain was over +5 miles/1000 ft, and in total, the net range loss for the 28 miles in the mountains was only 3 miles more than rated range miles, less therefore, than I would have seen if I had driven those mountain miles on a flat freeway at 75 mph. That, I have to say, blew me away. That's *very* efficient energy recovery!
By the time I got home, the average Wh/mile read 308, and I had 102 miles rated range left. This means that my 24 mile freeway drive reduced the range only by 22 miles, and that the whole 77 mile trip cost me 85 rated miles - most of the overage caused by the higher than EPA freeway speed.
By the way: In retrospect, the extra 8 miles of range loss on my first leg now seem totally accounted for, and then some, because I did climb 1000 ft in these first 24 miles, and with a 6 mile range loss per 1000 ft, that means that I only lost 2 miles due to speed. This also was reflected in the lower than expected range loss on my freeway drive home, even though it didn't give me the full 5 miles range gain I would have had with regeneration.
This car continues to impress me in new ways every day.