Is 83 miles with big elevation changes possible?

[TonyWilliams]

If the average air density is, say, 25% lower than sea level, how much does that skew the speed/range numbers?

Most of the range impact with respect to speed is pushing air. Rolling resistance is mostly linear, therefore the impact from density altitude will be significant.

How significant? I don't know in a tangible way. The problem for a test is that I can easily find a flat piece of ground to tell you the energy needed at sea level, but where in the world will I find that at 10,000 feet? An airport, maybe, but a runway is only one or two miles long, and even they aren't normally level in the mountains.

The best we could do is calculate a guess. Here's how I might suggest that. Hopefully, we'll find a nice level spot on a really hot day somewhere that somebody will gathering some solid data (we need the average miles/kWh).

That would have to be repeatable, both directions, with all the other variables to "standard" (tires, weight, wind calm; just a hot day at high elevation).

The best place that I've thought of to do that is the Bonneville Salt Flats area, with 4000 feet elevation and over 100 degree days in the summer. Driving the car at 60mph is a great benchmark, and we expect a value significantly greater than 3.9 m/kWh. Please note that ANY elevation change will skew the data, and that is the reason for bi-directional runs, and runs near water features... water tends to be level !

If the air is 25% less dense, and rolling resistance stays the same from sea level, then I would expect a 15% increase in performance.

If an airplane will travel 60mph at sea level with an indicated air density of 60mph, then it will travel 70mph at 10,000 feet elevation.

So, my rule of thumb is a 15% increase in range per 10,000 feet density altitude. For your trip, you will be significantly above 10,000 feet elevation, AND above standard temperature of 15C minus 2C per 1,000 feet elevation, or -5C. Your temperature is likely to be significantly above -5C in summer, therefore your density altitude (and range adjustment) even higher.

Tony

 

[dgpcolorado]

dgpcolorado,

Just curious, Is this road still open? Open year-round???

Yes, US 550 from Ouray to Durango is a major route that is kept open by the Colorado Division of Transportation year around, although it is closed from time to time in winter to clear avalanches. Snow closures usually range from a few hours to three days or so. Silverton is sometimes isolated for several days at a time. The alternate route via Lizard Head Pass near Telluride is much longer.

 

[dgpcolorado]

...So, my rule of thumb is a 15% increase in range per 10,000 feet density altitude. For your trip, you will be significantly above 10,000 feet elevation, AND above standard temperature of 15C minus 2C per 1,000 feet elevation, or -5C. Your temperature is likely to be significantly above -5C in summer, therefore your density altitude (and range adjustment) even higher.

Tony

Thanks for that. You may recall my air density numbers in the elevation thread. The reason I used STP for the first list is because the lapse rate seen at aircraft altitudes tends to break down close to the ground (as any resident of a city with an "inversion layer" learns). The lapse rate temperature is simply not relevant during summer here. But, of course, temperature does tend to be lower as one goes higher on a given day, with concurrent increased density.

Doing an experiment on flat terrain at high altitude aside, I was thinking it might be possible to just plug density numbers into drag equations and get some sense of "at 8000 feet 60 mph = 50 mph at sea level, at 20º C" or some such thing.

I'm aware that the altitude density effect is quite significant because I get much better gas mileage in my ICE car here in Colorado than when I take it to sea level. It would be nice to quantify it. I'm hoping it would help me in doing a trip like the one I've outlined in this thread, in addition to more routine routes that may stretch the LEAF range here, especially in winter.

 

[edatoakrun]

dgpcolorado,

Just curious, Is this road still open? Open year-round???

Yes, US 550 from Ouray to Durango is a major route that is kept open by the Colorado Division of Transportation year around, although it is closed from time to time in winter to clear avalanches. Snow closures usually range from a few hours to three days or so. Silverton is sometimes isolated for several days at a time. The alternate route via Lizard Head Pass near Telluride is much longer.

I would not suggest trying this drive for the first time in January with a storm approaching...

I can't think of any roads above 7,500 ft that are plowed year-round here in Northern CA. I'd like to drive the Lassen hwy 89 (8500 ft pass) again before they close it-usually from about now till July.

 

[dgpcolorado]

I would not suggest trying this drive for the first time in January with a storm approaching...

I can't think of any roads above 7,500 ft that are plowed year-round here in Northern CA. I'd like to drive the Lassen hwy 89 (8500 ft pass) again before they close it-usually from about now till July.

It is very different here. This whole state is higher than most other places in the lower 48; the lowest elevation in Colorado is 3315' near the Nebraska/Kansas border. Even Interstate 70 passes through the Continental Divide via the Eisenhower Tunnel at 11,158' and over Vail Pass at 10,666'. However, we don't get nearly as much heavy, wet snow as is seen in the Sierra Nevada and Cascade Mountains (aka "Sierra Cement" and "Cascade Concrete" ). The cold, dry winter air has less moisture content. That makes it easier to keep roads open.

 

[TonyWilliams]

Your ICE car gets great mileage for two reasons, one of which does not apply to the LEAF. With less oxygen, less fuel must be mixed to keep close to the ideal fuel mixture. Less fuel means better fuel economy (and less power).

The temperature lapse rate does indeed apply, because that is the foundation for determining density altitude. The fact that the earth is much hotter than the air at a given elevation is no surprise... It just raises the density altitude. The two basic simple ingredients remain; pressure altitude and temperature.

If you are at 10,000 feet on a warm day, the density altitude may be many thousands of feet higher. That's the data that you use.

rate seen at aircraft altitudes tends to break down close to the ground (as any resident of a city with an "inversion layer" learns). The lapse rate temperature is simply not relevant during summer here. But, of course, temperature does tend to be lower as one goes higher on a given day, with concurrent increased density.

Doing an experiment on flat terrain at high altitude aside, I was thinking it might be possible to just plug density numbers into drag equations and get some sense of "at 8000 feet 60 mph = 50 mph at sea level, at 20º C" or some such thing.

I'm aware that the altitude density effect is quite significant because I get much better gas mileage in my ICE car here in Colorado than when I take it to sea level. It would be nice to quantify it. I'm hoping it would help me in doing a trip like the one I've outlined in this thread, in addition to more routine routes that may stretch the LEAF range here, especially in winter.

 

[dgpcolorado]

Your ICE car gets great mileage for two reasons, one of which does not apply to the LEAF. With less oxygen, less fuel must be mixed to keep close to the ideal fuel mixture. Less fuel means better fuel economy (and less power).

That makes sense. Altitude was more of a problem in the days of carburetors, which had to be adjusted. Now that essentially all cars are fuel-injected, the oxygen sensor is used to adjust the fuel mixture automatically. But I hadn't considered that the lower fuel/air mixture might give greater mileage because I assumed that one would compensate for the reduced power with different accelerator and transmission inputs. I am still inclined to believe that reduced drag at higher speeds is the greatest factor in increased mileage but I couldn't begin to prove it.

The temperature lapse rate does indeed apply, because that is the foundation for determining density altitude. The fact that the earth is much hotter than the air at a given elevation is no surprise... It just raises the density altitude. The two basic simple ingredients remain; pressure altitude and temperature.

If you are at 10,000 feet on a warm day, the density altitude may be many thousands of feet higher. That's the data that you use.

Since I have no practical way to measure density altitude I am just trying to get a handle on the change in drag/range at a given air density delta, other things being equal. If, as you suggest, there is a 15% increase in range (at 60 mph?) for 10,000 feet at -5ºC and my temperature is 10ºC, I guess I can assume that it will be somewhat greater than that. What I am trying to grasp is what the range increase would be for a given air density decrease at a given speed.

At low speeds this change would be trivial. At higher speeds it could be quite significant. Perhaps what I need is a pitot tube and an airspeed indicator...

 

[TonyWilliams]

I'm on the iPhone, so can't easily look up the numerous online density altitude calculators, but you CAN calculate it! You know the elevation, and the temperature. Ignore the minor difference of pressure altitude.

Use 1.5% per thousand feet density altitude, and you'll be in the hunt. If it's 25C at 10,000feet, you can just use 29.92 in for pressure, and 1 for humidity, and get 13,350 feet density altitude.

1.5 * 13,000 = 19.5% increase in range at 60 mph indicated.

 

[TonyWilliams]

http://wahiduddin.net/calc/calc_da.htm" onclick="window.open(this.href);return false;

 

[Herm]

I'm not sure its appropriate to apply airplane air density data to cars, the air close to the road surface is sticky and could be turbulent.. but colder air should decrease the range in electric cars, and colder tires also have more drag.

 

[TonyWilliams]

I'm not sure its appropriate to apply airplane air density data to cars, the air close to the road surface is sticky and could be turbulent.. but colder air should decrease the range in electric cars, and colder tires also have more drag.

We stipulated that rolling resistance was the same. No correction was made for cold tires or hot tires. We aren't factoring for cold or hot air for electric car (batteries?). Those would be entirely different. Purely an air density on range calculation. What if the temperatures were 70F at 10,000 feet?

I'm not sure what turbulent and sticky air you're referring to.... the air that is half the distance, or less, of the length of the wing is actually the most "slippery" to an aircraft, and is referred to as "ground effect".

More than one airplane has crashed off the end of the runway in ground effect.... just enough power to get off the ground, but not enough to climb out of ground effect.

As I stated, ideally there would be a test. A car has to push air just like a plane, or a rock, or a bird, or anything else moving through the air. Just factoring the air density, there should be about 15% increase in range at 10,000, or about 1.5% per 1000 feet. Any other variable is just that, another variable.

 

[abasile]

As I stated, ideally there would be a test. A car has to push air just like a plane, or a rock, or a bird, or anything else moving through the air. Just factoring the air density, there should be about 15% increase in range at 10,000, or about 1.5% per 1000 feet. Any other variable is just that, another variable.

6750' might not be a bad altitude at which to conduct a test. One would have to secure uninterrupted access to the tarmac at the Big Bear City, CA airport for a range vs. SOC test at a mostly fixed speed, to compare with an equivalent run conducted at or near sea level. Tony, do you have any connections at the airport up here? I sure don't.

I will say that I seem to get very decent efficiency driving around the San Bernardino Mountains between Crestline and Big Bear, in spite of the many ups and downs. Doing 100+ miles per charge would not be a problem if needed, assuming no net altitude change. Of course, I have to qualify that by saying that I do have some hypermiling tendencies.

 

[TonyWilliams]

Tony, do you have any connections at the airport up here? I sure don't.

The Big Bear runway is remarkably level. I'm surprised.

Elevation: 6750.1 ft. (Rwy8) 6751.4 ft. (Rwy26)

Dimensions: 5850 x 75 ft. / 1783 x 23 m
Surface: asphalt, in good condition

It's hard to imagine that we'd get useful information in just a little over a mile at a time.

 

[abasile]

It's hard to imagine that we'd get useful information in just a little over a mile at a time.

That's the big downside. You'd have to do loops, which would mean speed changes.

A really level section of freeway at altitude would work better. But somebody would have to get a LEAF to such a location. Perhaps one of the LEAFers near the Front Range of Colorado could do that for us.

 

[SanDust]

Thanks to regenerative braking, increased mass is less of a problem with EVs than with ICE cars (the "low hanging fruit" for improving EV efficiency is aerodynamic drag). But more mass probably does mean greater losses in rolling resistance and the like.

In theory, the momentum (MV) of motion and potential energy of hill climbing can be recovered

In order for regen to work as you're suggesting you have to GET to the top of the climb. If you run out of energy before the summit you can't recover it. If it takes four bars of the SOC for the vertical part of the climb, and you start with four bars, then you're not going to make it since you'll need a bar or two for the horizontal part of the climb. This will be true despite that fact that if you reached the summit regen then the vertical part of the descent would provide you with all the energy and more needed for the horizontal part of the descent.

Rolling resistance is mass X gravitational constant X coefficient of rolling resistance so yes, taking five people, especially if they're large, would not be a good idea. The bigger problem with five people is that the energy needed for the climb is mass X gravitational constant X height of the climb. That's probably a 49X larger number.

 

[dgpcolorado]

...As I stated, ideally there would be a test. A car has to push air just like a plane, or a rock, or a bird, or anything else moving through the air. Just factoring the air density, there should be about 15% increase in range at 10,000, or about 1.5% per 1000 feet. Any other variable is just that, another variable.

Yes, that's really the sort of number I am looking for. Not so much for the trip listed in this thread, because speeds are fairly low on those high passes, but for routine driving at home (from 8000' to 5700'). The lowest elevation within LEAF range, without interim charging, of my house is about 5760'. And the highest speed limit within that circle is 60mph.

 

[dgpcolorado]

In order for regen to work as you're suggesting you have to GET to the top of the climb. If you run out of energy before the summit you can't recover it...

You are absolutely right and I hadn't considered that basic fact with regard to carrying extra mass.

 

[HighDesertDriver]

Since I have no practical way to measure density altitude I am just trying to get a handle on the change in drag/range at a given air density delta, other things being equal. If, as you suggest, there is a 15% increase in range (at 60 mph?) for 10,000 feet at -5ºC and my temperature is 10ºC, I guess I can assume that it will be somewhat greater than that. What I am trying to grasp is what the range increase would be for a given air density decrease at a given speed...

Send me your location via PM and I'll look up the phone number for local automated reporting stations that you can call. Most are at airports, but some are in passes frequented by general aviation. With few exceptions, density altitude is reported along with winds and weather.

 

[GREENEV]

I live in Denver, Colorado. I just ordered a Leaf. I wanted to know if anyone has any hard facts about driving a Leaf at sea level vs at high elevation?

 

[abasile]

I live in Denver, Colorado. I just ordered a Leaf. I wanted to know if anyone has any hard facts about driving a Leaf at sea level vs at high elevation?

All else equal, you will definitely get better range at altitude than at sea level thanks to the thinner air (see the rest of this thread). The LEAF that climbed Pike's Peak earlier this year had an advantage over the internal combustion vehicles, in that its electric drivetrain is not affected by altitude. As far as I know, no one has specifically measured this advantage in a LEAF, though. All I can say is that I do well at 6100'.