Question about Tesla range in the mountains

Alpine Road Trip

I left a note in this Forum http://www.teslamotorsclub.com/showthread.php?t=4215 not so long ago.
The Roadster is an all out sports car and you will tend to drive it on mountain roads accordingly. You would have to drive in tandem to get a meaningful comparison. I found that recuperation on the way down is very important and the roadster does that apparently very well. So as a rough approximation, your consumption, if the way down is included and fluently driven, will be not more than about 10-20% higher than the equivalent distance driven at comparable speeds on a flat, equally winding road, with accelerations and decelerations. In numbers say: 160 instead of 140 Wh/km. In my experience headwind on a motorway has a more dramatic effect.

Yes, headwind can be a pretty nasty component. Think of it this way: above 55mph drag becomes a very large component of total energy use. The headwind just raised your relative speed directly increasing your drag. 15mph headwind, and the (aerodynamic) energy drain is equivalent to 70mph ! (Not the drivetrain and rolling resistance, of course.)
The numbers for the LEAF will be different, naturally, but look at the proportion that "aerodynamic" represents of the "total" on the Wh/mile graphs found here: Roadster Efficiency and Range and more partiularly here:



(And winds in the mountains ... can be trickier and stronger too.)

And WELCOME to this forum ! :smile:

LEAFguy said:

For those of you that live in or near mountains, how have you found your range to be impacted by driving in them.

Click to expand...

The RAV4-EV, while older, less aerodynamic and using a different battery chemistry, is at least of a similar weight and range to the Leaf. The RAV4-EV FAQ (http://www.evnut.com/rav_faq_owner.htm) says:

"Every 1000' of elevation consumes an extra 6-7% SOC. And if you return to your starting elevation, all but 2-3% of that SOC loss can be replaced."

We haven't driven our RAV4-EV over mountains to verify those numbers. I have driven my Tesla over several mountain ranges, but I have not measured carefully. Tom Saxton did once (http://www.saxton.org/tom_saxton/2009/09/), and the numbers turn out to be eerily similar. He lost about 6.5 ideal miles per 1,000 feet of elevation gain (he went up 6,200' over 83.7 miles, and his ideal miles dropped 125, which is 41.3 miles over the distance traveled. 6.2 1k' * 6.5 miles lost per 1k' = 40.3 miles lost), and gained 4 ideal miles per 1,000 feet of elevation loss (he went down 6,200' feet over 85.1 miles, and his ideal miles dropped 60, which is 25 less than the distance traveled. 6.2 1k' * 4 miles regained per 1k' = 24.8 miles regained).

Let's assume the Leaf is affected similarly, and that you are driving in a manner (i.e. 55mph in decent weather) that would normally net you 100 miles of range. It then sounds like you can compare a mountain route to a non-mountain route in the fashion:

If you drive to a city 60 miles away on a flat route, you will arrive with 40 miles of range left. Half-way there, of course, you will have 70 miles of range left.

If you drive to a city 60 miles away with a 4,000' pass in the middle (and you start and end at sea level), at the pass you will have about 44 miles left. When you arrive at your destination, you will have 30 miles left.

So a mountain costs you 2.5 ideal miles per 1,000 feet, which really isn't bad. The only thing you need to watch for is that is AFTER you decend; if you plan on charging up near the top, you have to have enough in reserve to be able to spend 6.5 ideal miles per 1,000 feet.

Great data, Chad!

One additional thing to keep in mind, Ernie. The Tesla has very strong regen. And although quite a bit of the "range" you gain back on the downhill side is due simply to gravity (less energy expended over the same distance compared to flat driving), a bunch (on the Tesla) is gained back due to regen (would be great to quantify this ... but I don't have the data). On the LEAF little is known so far as to its "strength" of regen ... how much will it put back into the battery on steep downhills ? Only the steepest of downhills for a Tesla require friction braking (read: heat loss); at all other times you are charging the battery, thus extending your range, even when using cruise control. On a LEAF (if you want to follow the speed limit laws) I would expect friction braking to be necessary on many downhill stretches (unlike the Roadster), especially due to the extra weight, but who really knows at this point ? (So ... all else being equal (which it's not) ... a Roadster would put back more energy into its battery pack than a LEAF, but that's only my personal guess at this point.)

Hybrids do something similar. On our Highlander Hybrid, when we drive over the Santa Cruz Mountains, the battery gauge shows the (~1.5kWh) little pack getting down to near empty by the top of the hill, but then we basically coast down the other side and end up with a near full pack down at the bottom. Graham might have something to say about all of this as I think he commutes over the same hill in his Tesla.