How much does elevation climb and drop affect range?

[chibi_kurochan]

Attached is a potential route leg. Missoula, MT to Lethbridge, AB. Net elevation across the leg is a drop of approximately 200'. A lot of the trip is along river valley bottom. However there is at least one pass that I've identified, at Summit, MT. It's elevation is 5338'. What's the rule of thumb on losses for up-down, assuming dry highway and mindful driving to avoid friction braking as best as possible?

Assuming a full charged fresh M3 LR, high summer months so hopefully no snow, does this leg look like it could be an issue?

Here’s a detailed look at efficiencies:
Charged EVs | A closer look at energy consumption in EVs

 

[vinnie97]

Downshifting should limit the amount of excessive breaking required downhill, right? Hopefully, the Kalispell charger will arrive sooner rather than later (I.e. by the time your vehicle is delivered) so that this route will be an afterthought. Definitely some of the most bucolic scenery in North America through this route.

 

[ℬête Noire]

The drag is directly proportional to density, right? So once I've got the density estimate (with a fudged temp drop), do a %Δ from nominal sea level density, then multiply that by the percentage of energy used that's due to wind drag (I've got tables/graphs of that for the M3 from a prior thread) and that gives me a rough expected percentage of drop in energy usage, flip it to get increased range percent, and boom.


P.S. Eyeballing it, that elevation chart does suggest that heading in the other direction could indeed be even harder because of that sizable hill near the end. I'll have to work the kWh on that.

 

[dhrivnak]

I lose very little over passes as what I lose going up I gain on the downside. I lose about 7 miles going up and gain about 6 going down 1000’. So maybe. 15% hit on a pass.

 

[ℬête Noire]

Downshifting should limit the amount of excessive breaking required downhill, right? Hopefully, the Kalispell charger will arrive sooner rather than later (I.e. by the time your vehicle is delivered) so that this route will be an afterthought. Definitely some of the most bucolic scenery in North America through this route.

I've been through that side of MT before. Once on bus to Whitefish ski trip, once to a convention in a historic mining town on the Idaho border. Definitely gorgeous scenery.

Not counting on any of the Grey Pins, though. Or I'd be inclined to save myself 1500km and just go straight up through ND, for either the trip up or back.

 

[SageBrush]

However a 70mph to 30mph speed drop translates to only about 45m (150ft) of elevation change, if my math is right. On say a 500m pass the benefit of feathering like that will get heavily diluted.

My math comes out about the same*, But look at the elevation map that dgpcolorado posted: there are no 500 meter downhills without intervening climbs. I could only identify one downhill of about 500 feet where regen is clearly needed (although less than this calc implies since you use some of the potential energy to offset the 10-15 kW of opposing frictions and you might be able to speed up 5-10 mph towards the bottom of the descent to be bled off shortly thereafter.)

*
h in meters
v in meters per second
h= 0.05*(v2-v1)(v2+v1) (expression written to make parameterization easier for mental arithmetic)

 

[ℬête Noire]

there are no 500 meter downhills without intervening climbs.

It's not really the downhills, it's the climbs. Because I think the idea is you're scrubbing speed to trade to coast up elevation gain? You are shifting to neutral so you can take your foot clear off the accelerator, thus drawing zero current from the battery, right?

This leg starts, unless I'm reading the scales wrong, with a 300m (1000ft) one right out of the gate. I'm not super sure about the X-axis, it doesn't have finer gradient marks so it's challenging to eyeball and work out the % grades involved. I'll play around with gpsvisualizer.com some more.

 

[SageBrush]

It's not really the downhills, it's the climbs. Because I think the idea is you're scrubbing speed to trade to coast up elevation gain? You are shifting to neutral so you can take your foot clear off the accelerator, thus drawing zero current from the battery, right?

It can be either, but my calcs were for the downhill portion.
To summarize: start the descent at a slow(er) speed.

No gear changes required. Just let the end of the ascent take off some speed.

 

[ChadS]

I haven't seen measurements for the Model 3 yet, but given its weight I would assume that it would cost about 7-8 miles of range for every 1,000 of elevation gain.

Whoops. Above, I just threw out miles from other cars with a similar weight. But the 3 is notably more efficient than other EVs I had been comparing it to, so the number of miles lost will be higher than that. I should have said kWh lost instead of miles.

 

[ℬête Noire]

It can be either, but my calcs were for the downhill portion.
To summarize: start the descent at a slow(er) speed.

The uphill calculation is the same as down, with a sign inverted if you want to keep strict track of that. What goes up must come down, what comes down must have gone up.*

* assuming net elevation change across the whole trip, which is a decent approximation here with only 200ft difference from start to end of 300mi trip.

 

[ℬête Noire]

Whoops. Above, I just threw out miles from other cars with a similar weight. But the 3 is notably more efficient than other EVs I had been comparing it to, so the number of miles lost will be higher than that. I should have said kWh lost instead of miles.

Not necessarily. If it's mass is proportionally smaller, it comes out to the same thing. Thus the reason up thread for my calculation of work based on car mass, G, and elevation change. Then converting that kWh to miles using an assumed M3 Wh/mi.

EDIT:
1000ft = 305m
car + 1 rather chubby occupant (driver) = 1850kg

305*9.8*1850 = 5.53MJ = 1.536013889kWh

1.536013889kWh / 240Wh/mi = 6.4mi

EDIT2: Adjust miles as driving style varies the mileage.

 

[ChadS]

I agree that two cars of equal mass will do equal work carrying the car up hill. But then to get miles, you have to use the target vehicle's efficiency, which you did. I did not in my first reply to you; I (implicitly) used the efficiency of a similar-weight-but-very-different-efficiency vehicle.

 

[mspohr]

Attached is a potential route leg. Missoula, MT to Lethbridge, AB. Net elevation across the leg is a drop of approximately 200'. A lot of the trip is along river valley bottom. However there is at least one pass that I've identified, at Summit, MT. It's elevation is 5338'. What's the rule of thumb on losses for up-down, assuming dry highway and mindful driving to avoid friction braking as best as possible?

Assuming a full charged fresh M3 LR, high summer months so hopefully no snow, does this leg look like it could be an issue?

I did a similar drive a few years ago in my S85D. Did a little different route. SuperCharged at Canmore and drove to Fernie where we stayed overnight and charged at a municipal charger next to the town hall. Neat town and beautiful valley.
We then drove East to Pincher Creek then South to Glacier. We stayed at Many Glacier Lodge (beautiful old lodge and hiking with the Grizzlies) then drove through the park to West Glacier where we camped and charged at San-Suz-Ed RV park (they also have B&B rooms).
From there we drove to the Missoula SuperCharger.
I don't think you'll make the trip as you have it mapped out. Going up hill takes significant energy and you may run out of steam at the pass. I'd recommend taking your time to stop and charge at RV parks along the way. It's a beautiful part of the world and no need to race through it. Check out PlugShare, there are lots of options.

 

[ℬête Noire]

I did a similar drive a few years ago in my S85D. Did a little different route. SuperCharged at Canmore and drove to Fernie where we stayed overnight and charged at a municipal charger next to the town hall. Neat town and beautiful valley.

I skied there a few times, in a century past.

That charger is a Sun Country Highway one, right?

 

[SageBrush]

The uphill calculation is the same as down, with a sign inverted if you want to keep strict track of that. What goes up must come down, what comes down must have gone up.*

* assuming net elevation change across the whole trip, which is a decent approximation here with only 200ft difference from start to end of 300mi trip.

Sure, but that misses the point that ascents are usually broken up by descents where you can spread out the kinetic energy. As I said, look at dpgColorado's elevation map.

 

[ℬête Noire]

Sure, but that misses the point that ascents are usually broken up by descents where you can spread out the kinetic energy. As I said, look at dpgColorado's elevation map.

I looked at it. Again, it isn't the easiest to read because of lack of small gradients but I see at least 3, maybe 4, 300m+ climbs without intervening descents to break them up. Looks to me like also a 5th continuous climb that's also over a 45m, but not as much so as the others, around the 35mi mark.

Pretty typical western mountain traversing drive.

EDIT: Or am I just reading that graph all wrong????

 

[SageBrush]

I looked at it. Again, it isn't the easiest to read because of lack of small gradients but I see at least 3, maybe 4, 300m+ climbs without intervening descents to break them up. Looks to me like also a 5th continuous climb that's also over a 45m, but not as much so as the others, around the 35mi mark.

Pretty typical western mountain traversing drive.

EDIT: Or am I just reading that graph all wrong????

You should not care about long ascents.
The goal here is to minimize regen on descents (and of course no friction brakes.)
Since the descents are rarely very long and steep, the extra potential energy can be diverted to kinetic energy safely IF you bleed off some speed before starting a descent.

I apologize for apparently making this complicated when it is actually little more than common sense.
Perhaps an example would help:
Imagine a hill that you will going up, driving level for a short distance, and then going down. The speed limit is 65 mph throughout.

The usual, inefficient way people drive this hill is to travel at 65 mph from the bottom to the top, and then to ride their brakes on the way down.

I drive 65 mph most of the way up the hill but let off the go pedal before I reach the top. By the time the car starts to go down the hill my speed is ~ 50 mph and then the speed rises as I go down the hill without any braking. In a perfect world my car speed is again 65 mph at the bottom of the hill.

The Missoula to Fort Mcleod route is ~ 300 miles and has some 33 descents (eyeballing dgp's map) that total about 9000 feet

A large fraction of the 9000 feet of potential energy down can be handled without regen/brake use (at least towards Ft. Mcleod; the other way less so.)

For example, one of the steeper descents is from Glacier National Park heading down the Swiftcurrent Pass Trail. But even that road's 3 miles of overall descent is broken up by level segments that will bleed off speed:

You just have to think ahead ... and hope you do not have a moron on your butt urging you to drive faster before the impending descent.

 

[David99]

I believe it's aprox 6 miles extra range for each 1000 feet elevation gain and 5 earned back going down. It almost evens out. Best way to guess it is if you program it into the car's navigation the and trip estimate will show your energy usage.

The recent update of 'Scan My Tesla' shows the DU efficiency in realtime. It seems regen and driving are equally efficient. Of course when you regen you have to add the charge losses of the battery. It is more energy efficient to go down slower and use regen than coasting down in Neutral. Higher speed cause higher aerodynamic losses which means energy is lost. Even though regen isn't 100% efficient it is always more efficient that throwing energy away into the air.

 

[David99]

^ Denver Supercharger Station to Silverthorne Supercharger Station via the Eisenhower tunnel [11,158 ft (3,401 m)].

It's not necessarily how much energy you end up with at your destination it is how much you have left at the high point. This is something of an extreme example, however.

Yes that's a good example. Once you drive it you will see it never uses the energy down to the sharp peak. Why? Because the navigation system is sampling the elevation thinking you have to go over the peak of the mountain, while in reality you go through the tunnel which has very little elevation change.

 

[ℬête Noire]

You should not care about long ascents.
The goal here is to minimize regen on descents (and of course no friction brakes.)
Since the descents are rarely very long and steep, the extra potential energy can be diverted to kinetic energy safely IF you bleed off some speed before starting a descent.

I apologize for apparently making this complicated when it is actually little more than common sense.
Perhaps an example would help:
Imagine a hill that you will going up, driving level for a short distance, and then going down. The speed limit is 65 mph throughout.

The usual, inefficient way people drive this hill is to travel at 65 mph from the bottom to the top, and then to ride their brakes on the way down.

I drive 65 mph most of the way up the hill but let off the go pedal before I reach the top. By the time the car starts to go down the hill my speed is ~ 50 mph and then the speed rises as I go down the hill without any braking. In a perfect world my car speed is again 65 mph at the bottom of the hill.

The Missoula to Fort Mcleod route is ~ 300 miles and has some 33 descents (eyeballing dgp's map) that total about 9000 feet
View attachment 284026

A large fraction of the 9000 feet of potential energy down can be handled without regen/brake use (at least towards Ft. Mcleod; the other way less so.)

For example, one of the steeper descents is from Glacier National Park heading down the Swiftcurrent Pass Trail. But even that road's 3 miles of overall descent is broken up by level segments that will bleed off speed:

View attachment 284027

You just have to think ahead ... and hope you do not have a moron on your butt urging you to drive faster before the impending descent.

Ah, that's what you're getting at. Much clearer now, thank you.

In mountains I have long crested like that primarily for a different reason, braking distance on the down slope is drastically lengthened. I'm doubly on top of slowing coming up on the crest if it's a new-to-me-road, if I don't have some reasonable sense of what's coming up. I do not want to have to be already on the brakes before an urgent situation develops in front of me.

I was under the impression that, except maybe perhaps in the case of very tight switchbacks, that Tesla's regen was stronger than that. That short of something like a 15% grade, with your foot full-off the accelerator the drivetrain would end with a net dropping of vehicle speed.

Question, does anyone know if you use the accelerator pedal to signal to the system that you want to maintain a certain speed but the motor doesn't require energy input to do so, will it draw zero current from the battery? Is it smart enough energy management to flip between regen braking and zero draw coasting, as needed? If not will cruise/TACC handle that better?

P.S. The deeper the dig the more it becomes clear that it'll be a lot harder to make the full distance headed South, rather than when headed North.