I suppose the Phoenix-Flagstaff stretch (esp the Campe Verde to Flagstaff) must be just such a stretch because ZBB's numbers are third time I've see someone come close to that "+7 per 1000 up, -3 per 1000 down" calculation on the drive.
Just be careful to keep excess usage caused by speed and driving style separate from potential energy (altitude) gain and loss. What I have done (nerd alert) is to correct my battery energy for current elevation relative to destination elevation, then calculate the ratio of rated miles used to actual miles traveled. When doing this, I have found that I get almost everything back going down that I use going up. Eisenhower Tunnel to Silverthorne and Wolf Creek Pass to Pagosa are both 10 rated mile regen hills. Even on those, I only lose a few miles. Good hypermile technique is also needed, or at least don't pump the accelerator too much, and slow down early enough that you don't need to use the brake very much entering turns.
In my opinion, backed by a lot of Colorado mountain driving, is that the 7 up, 3 down is a myth that has been perpetuated with little experimental data to back it up.
Many, including me, consider
EVTripPlanner to do very good modeling. A drive that I do regularly is Pagosa Springs, CO to Silverthorne, CO. Put those cities in with an 85 and 19" wheels, the rest default. When you do this, it comes out with 307 Wh/mi (not bad), but it has 12,264 feet up and 10,558 feet down. As another case, put Phoenix to Flagstaff and back into
EVTripPlanner. At first, the result came out at 360 Wh/mi for the round trip; was I wrong? Then I noticed that my Colorado route had an average speed of 55 mph, and the Arizona route had an average speed of 68 mph. When I turned down the speed limit multiplier to 0.85 to get an average speed of 57 mph, the round trip was 305 Wh/mi. Here are the detailed results at the lower speed:
| Route | Distance | Wh/mi | Energy | Up | Down |
| PHX->FLG | 145.5 | 376 | 54.7 | 10,371 | 4,618 |
| FLG->PHX | 145.5 | 234 | 34.2 | 4,618 | 10,371 |
| Tot/Avg | 291.0 | 305 | 88.9 | 14,989 | 14,989 |
This supports my claim. The real user of excess energy on this Phoenix/Flagstaff round trip is the high speed limit on the interstate, not the loss of up versus down. With speeds near 55, you can get rated miles. Go faster and you use more energy per mile. On the other hand, the MS recovers almost all of the excess energy going down hill that was used going up.
As a further confirmation, I tried the Savannah, GA to Jacksonville, FL route. This is about as flat as it comes. The distance is 139 miles, and at a 1.0 speed limit factor, the average speed is 70 mph and the mileage is 357 Wh/mi. At .83, I get 58 mph and 293 Wh/mi. So according to
EVTripPlanner, there is a little more energy used for these very mountainous routes versus the low country of Georgia, but even with these extremes, it is only 4% loss or 12 miles on that 15,000 foot up and down extreme. That's less than 1 net rated mile per 1,000 feet up and down!
My recommendation, use 7 rated miles per 1,000 feet up, and 6 down; and you will be very close.
Just remember, speed costs energy. As a corollary, wind can be a big effect. As opposed to altitude and potential energy, and as the physicists would say, wind is a non-conservative force; you never get back what you put in... :wink:
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Cottonwood - I think the only exception to your downhill range recovery rule is if people are doing full range charges or if the batteries are quite cold. In those two circumstances, I couldn't really make meaningful use of much of the regen energy for the first 15-20 miles driven. Has that been your experience as well?
So, if you're charging at the top of a steep hill, that argues for doing a little less than a full charge and letting gravity do the rest for you. Saves time too (as I can attest from my Kingman to Barstow and Tejon Ranch to La Mesa runs earlier this month, both completed in my 60 with 1 mile of range left in the tank when I arrived at my destinations).
I agree completely with the full range charge and regen issue. You get very little regen for the first mile or two, some after 5-10, and almost everything after 15-20. The one exception is long, continuous descents even after 50 miles. After a kW-hr or so of big regen (>200 Wh-mi regen), I have seen the Supercharger taper charge limits take effect. That can hit you even at 80% SoC. The answer on a reasonably spaced Supercharger route is never charge to more than what you need with some margin. Once again,
EVTripPlanner is a great predictor. My practice is to add 10-20% to that, more if the wind/weather looks really bad.
