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Range performance in mountains: comparing steep uphill to descents

Hello everyone, this is my first post here. My father just ordered an S and I have been following the progress of Tesla Motors with great interest over the past few years.

I have a question about how much more quickly Rated Range declines when ascending long grades, such as the western slopes of the Sierra Nevada mountains from the California Central Valley floor to Tioga Pass, compared to driving an equivalent distance on the flats, and if there is in fact a more rapid loss of range going uphill is there a corresponding conservation of Rated Range when making long descents due to regeneration?

I live in the San Francisco Bay Area. My wife and I like to take trips to the mountains and based on the map at http://www.teslamotors.com/supercharger of Supercharger stations that are being built out over the next couple of years, the closest station to the Sierra Nevada mountains on the west side is at Folsom, just east of Sacramento. A charge at that station will get an S85 to the South Lake Tahoe area and back, but it won't make it to the Yosemite / Sequoia area. Many of the places we stay at in the mountains do not yet offer a 240V outlet to their guests. We also like to go car camping where electrical outlets are even scarcer.

Currently we take our 2008 Prius on long trips, and from our house to the mountains and back typically average about 45mpg.

It is interesting to note on the Supercharger station map that it appears that no stations are planned to be built in the next 2+ years along Hwy 99 in the Central Valley. That is disappointing, as a station in the Merced/Fresno area would be well placed to support drives into the central Sierra Nevada mountains. The map does show a future station slightly east of the Bay Area and south of Sacramento but the map has so little detail that I can't determine where it will be located.

Thanks,

Barry

It does gulp power on the way up, but you get about 80% of it back on the downhill if you stay off the brakes. I've found the car does really well on mountain passes based on several trips over the Grapevine, the range to the West of Coalinga (Harris Ranch), and the mountain range separating Oregon from California. It's a little scary going up as the mileage is dropping rapidly, but it's fun to watch the gauge recover on the way down.

This site will help you get an idea about how hills will impact range. You can choose your car, map your route, estmate your speed and get a good estimate.

http://www.jurassictest.ch/GR/

I think a good rule of thumb is a mountain pass costs about 6 miles for every 1,000 feet in elevation. Depends on speed, temp, AC, heat, wind, grade. etc...

Here in Colorado I have recently been up and over several mountain passes over 11,000feet elevation. Yesterday was an example. 195 miles round trip over Berthoud pass and back for some mountian golf (no charging). The up-and-over was 150, and return only 45 range miles. My very rough estimate is the 2.8% average elevation gain up 6,800 ft, about doubled the kwh burn. I do use almost constant cruise control. For all the mountain trips, I have seen the round trip range miles almost exactly equal flat range miles.
Nice to hear people in the hills with these great cars. Mountain driving all my years, I've never had so much fun....

Thanks for all the quick responses. On steep descents with the regenerative function set on maximum (or whatever the term is) can speed be controlled pretty easily with minimal brake use?

@chetb

That is one of the beauties of regen. It is much easier to control speed while going downhill and no unnecessary brake wear.

Here's another site for you, built especially for the Model S by one of our forum participants:

http://evtripper.com/planner/carview_beta/?id=goc

Hit the "Show Details" and "Advanced" buttons to input lots of parameters and to access lots of data.

My own experience was a drive from Seattle/Kirkland to Paradise, Mt. Rainier and back. I went from sea level to 6,500 feet in 121 miles, then returned. When I completed the 242 mile drive, I had 18 rated miles remaining. This was in February or March, when the weather was fairly cold.

As @jbunn has said, the rated miles get consumed pretty quickly on the way up, but on the way down, after about 40 or 50 miles, I had actually added about ten rated miles.

@chet
Minimal brake use coming down the eastern slope of the Rockies--primarily when behind a slow poke or hairpin turns.

I have yet to see my car "break speed" on cruise control on a down hill requiring a break assist.

In other words, I have descended down some 7% grades with speed control set to 75 and have never seen it hit 76.... I thought it could not but I guess if the hill is steep enough to trigger max regen then from there it will gain speed.

Do I have it right?

That's one of the really nice things about an electric car. In my ICE, it used to go over the cruise control set speed on the downhill. In the Tesla it maintains the cruse control speed on the flat, uphill, and downhill equally. Have never driven a hill yet that caused the car to exceed the set point for cruise.

I go over the Mt Rose Highway (Incline Village to Reno) regularly, and it's possible to descend from the summit (9000 ft) into Reno (4500 ft) without ever using the brakes while staying at or below the speed limit (provided there are no cars braking hard in front of you and no red traffic lights on the Reno side of the Mt Rose). Typically you will recover 95% of the potential energy you consumed on the way up. For an 85KWh Model S, you'll use about 7 extra rated miles for each 1000' of elevation gain, and you'll save about 6.5 rated miles for each 1000' descent (the downhill savings come from both the energy you don't use (100% recovery) as well as the regen (probably about 80% roundtrip efficiency for the S). The only thing that can mess you up is if you try to go downhill when the battery is in the top 20% or when the pack is cold (below 45F). In those situations regen can be limited, meaning you either have to use the brakes or go faster than normal, meaning that some of the potential energy gets lost to heat.

@ chetb@totheweb:

If you want some additional details, I listed some measurements on this post:

http://www.teslamotors.com/forum/forums/mountain-driving-some-numbers

chetb;
On most downslopes, regen will bring the car to a virtual stop, if you lift right off. It's strong. If not on CC, your foot position will be partially depressed, IOW, to reduce the regen.

Just drove back from Tahoe City to Napa. Started with 215 rated miles, and arrived in Napa with 65 rated miles, indicating rated miles of 150. The actual distance was 176 miles. And I averaged at least 70 mph with full A/C as it was 100+ most of the trip.

I think I could make it from Napa to TC assuming I had a range charge of 260 rated miles, and drove conservatively. But I normally use Folsom so that I arrive with with plenty of charge and can drive with flow of traffic. And love those free electrons!

mountain driving is one of the joys of owning a tesla. both an ICE and EV will use more power going uphill. however, the ICE will waste the downhill kinetic energy as heat and wear on the brakes whereas the tesla will convert that energy to potential energy in the battery. the lack of brake wear is icing on the cake.

It's about 0.5 kWh per 100 m height difference used while climbing up (in addition to the ~0.2 kWh/km driving) and about 0.4 kWh per 100 m height difference gained when descending ...
So with 85 kWh you can climb a hill of ~15 km height (twice Mount Everest) before you have to head down ...

One obvious tip about mountain driving: make sure you are ascending with as full a charge as you can get. If you get into the hills at the end of your charge you may run out before you can take advantage of the downhill regen. We just did the San Francisco, Arcata round trip. On our way back south, we made sure to stop at the Benbow Inn to "tank up" before starting our ascent. Having done that, we ended up getting 30 miles better range on the return south leg than we did on the north leg.

Just drove back from Tahoe City to Napa. Started with 215 rated miles, and arrived in Napa with 65 rated miles, indicating rated miles of 150. The actual distance was 176 miles. And I averaged at least 70 mph with full A/C as it was 100+ most of the trip.

I think I could make it from Napa to TC assuming I had a range charge of 260 rated miles, and drove conservatively. But I normally use Folsom so that I arrive with with plenty of charge and can drive with flow of traffic. And love those free electrons!


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