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Discussion Starter #1
Does anyone have information on the relative energy efficiency of the Bolt at various speeds?

What I'm trying to track down is the projected number of miles travelled per KwH of energy used at various speeds.

For instance, I found on my 2013 Leaf that at 67 mph my Leaf gets about 4.4 miles of travel per KwH of energy used. Above that speed I found that energy efficiency drops pretty dramatically. Below that it increases. No surprises here, but knowing this has helped me use the available stored energy in the most efficient manner for trips that neared the Leaf's maximum range.

This information would be helpful in terms of knowing the Bolt's optimal cruising speed in order to maximize range on longer trips.

I haven't been able to find anything useful on the GM or other web sites, but perhaps the more technically knowledgable among us would have some decent information on this. A simple graph showing a speed/miles traveled curve would be really helpful!

Happy 2017 EV motoring to all!!!
 

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Discussion Starter #4
Thx Zoomit! That's a decent start, albeit I don't think the curve will be quite as straight as you guesstimate considering the physics of drag as jupitermoon mentions (and my experience in the Leaf.) I appreciate the effort!
 

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That 4.4 M/KWH figure for the Leaf is pretty optimistic. Most Leaf drivers find that efficiency drops off quite a bit above 40-45 MPH, and drops dramatically above 60MPH. The Leaf has a lot of drag, though, especially from the big wheel wells, so if the Bolt is closer to the Tesla S than to the Leaf is slipperiness, it will do better.
 

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Thx Zoomit! That's a decent start, albeit I don't think the curve will be quite as straight as you guesstimate considering the physics of drag as jupitermoon mentions (and my experience in the Leaf.) I appreciate the effort!
Ah, well, it's kind of hard just to draw a line on a graph without doing all the background calculations. I am still tweaking my Bolt EV driving efficiency model, but it produced the previous graph.

There's frequently confusion between energy consumption and power and the equations that govern them. The below graphs on the left show the energy consumption, which is energy needed to go a given distance, plotted against speed. The graphs on the right show the power needed to go a given speed, plotted against speed. The upper and lower graphs have the same data, just plotted stacked vs overlaid. The key is that as speed increases the time to go a given distance decreases.



Drag is on the order of squared of velocity so that is why you see power rise sharply.
More accurately, the energy consumed to overcome aero drag rises as a square of velocity. The power needed to overcome aero drag rises as a cube of velocity. On the left graph, you can see the aero drag energy consumption is increasing as a square of velocity. The exponential growth in the equations is a V^3/V term that simplifies to V^2. On the right graph, you can see aero drag power increasing as a cube of velocity. The equations have just the V^3 term.

Ultimately, the power vs speed graphs on the right are not too relevant for discussions about EV range and efficiency. What matters more is how much energy is needed to go a given distance, as shown in the graphs on the left.

But back to your original question, go slower to go further. But be aware that the max distance at a steady-state speed is not safe on a highway since it's around 20 mph. I don't even plot that data since 1) no one is going to go that slow at a steady speed and 2) the uncertainties in my model grow too large at slow speeds.
 

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Discussion Starter #7
Leaf energy usage

That 4.4 M/KWH figure for the Leaf is pretty optimistic. Most Leaf drivers find that efficiency drops off quite a bit above 40-45 MPH, and drops dramatically above 60MPH. The Leaf has a lot of drag, though, especially from the big wheel wells, so if the Bolt is closer to the Tesla S than to the Leaf is slipperiness, it will do better.
It's not optimistic or imagined- it's what I've consistently gotten during my time with the Leaf. The Leaf displays this information in real-time and keeps a record of segments saved.

My best 1000 mile interval of mileage per KwH of energy usage at mixed speeds has been 4.5 and my worst has been 4.2. I would estimate that 90% of the 1000 mile segments I've traveled have been 4.3 or 4.4... mostly 4.4. My Leaf has travelled 35,000 miles.

When I'm on the freeway doing 67 mph the Leaf shows 4.3-4.4. Above that it drops considerably; for example at 72 mph it will show 3.9 miles per KwH.

Interestingly, I noticed when driving a friend of a friend's Tesla sedan that the Tesla's energy usage seemed to hover around 3.5-3.7 miles per KwH. This lower efficiency is probably a function of the Tesla's far higher weight.
 

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My best 1000 mile interval of mileage per KwH of energy usage at mixed speeds has been 4.5 and my worst has been 4.2. I would estimate that 90% of the 1000 mile segments I've traveled have been 4.3 or 4.4... mostly 4.4. My Leaf has travelled 35,000 miles.

When I'm on the freeway doing 67 mph the Leaf shows 4.3-4.4. Above that it drops considerably; for example at 72 mph it will show 3.9 miles per KwH.
I don't have any experience with the LEAF so I'd like to hear a little more to understand how you're getting this efficiency, especially since it's seems at least 10% higher than the EPA data.

Are you at high elevation, high temperature (AZ or NM)?

Are these numbers similar to what others are getting in the LEAF?
 

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When I'm on the freeway doing 67 mph the Leaf shows 4.3-4.4. Above that it drops considerably; for example at 72 mph it will show 3.9 miles per KwH.
Those numbers are indeed high. I hesitate to question them, but wonder if there is another factor involved, like skinny tires running at high pressures, or a subtle downgrade in the road. I can just manage them in mild weather with no heat, but in Winter at that speed, with my hard-compound snow tires, I'd be at about 2.8-3.0 M/KWH
 

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Discussion Starter #11 (Edited)
Leaf efficiency

I don't have any experience with the LEAF so I'd like to hear a little more to understand how you're getting this efficiency, especially since it's seems at least 10% higher than the EPA data.

Are you at high elevation, high temperature (AZ or NM)?

Are these numbers similar to what others are getting in the LEAF?
I live in the Oakland Hills in the Bay Area which has a mild climate. Most of my driving (95+%) is done on level roads except for the last half mile up to and down from my home.

I didn't realize until posting this thread that my numbers were at all unusual. I don't do anything special, other that frequently driving in "B" mode in slow traffic on the freeway and all the time when I'm on city streets and roads. I am no speed demon, but I like to accelerate briskly from stops. I try not to exceed 67 mph on the freeway. I would guess that my mileage is split about 60-40 freeway vs. city streets. I am single and do most of my travel alone (I weigh 165 lbs.) and with my faithful companion Rosie The Wonderdog (she weighs 50 lb.) so I guess I'm not carrying around a lot of weight.

My range has dropped from around 90-92 miles when the car was new to around 85-88 miles now.

I could take a picture of the history of my energy usage if that would be helpful to folks.
 

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Zoomit...

Out of curiosity, what have you been getting over the lifetime driving on your Spark EV?

I've almost 37K on mine and I've been averaging 5.7mi/kWh.

Cheers.
 

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I think that the low speed driving in B mode is inflating the overall average for V7i7c, along with (I'm guessing) very little climate control use.
 

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More accurately, the energy consumed to overcome aero drag rises as a square of velocity. The power needed to overcome aero drag rises as a cube of velocity.
Energy consumed per what, per mile or per minute? The first is indeed a square (and translates to efficiency, if you don't consider getting somewhere faster as being more efficient ;)), but the second is a cube (and translates to power): more energy per mile * more miles per minute :nerd:

This also explains why adding 20 MPH headwind had a bigger negative effect than driving 20 MPH faster:

When adding 20 MPH to driving speed, energy consumed per minute increase cube-wise, but energy consumed per mile increases only square-wise.
When adding 20 MPH headwind, both energy consumed per minute and energy consumed per mile increase cube-wise, as your speed does not increase.


When it comes to optimal efficiency, I am led to believe that an e-motor does not need a certain load in order to achieve best efficiency, as an ICE does. Up to a certain speed, increased efficiency of an ICE can and will outweigh increased drag, which means the most efficient speed for an ICE propelled car is not 'as slow as possible'. If I am not mistaken, E-motors do not see increased efficiency with increased load / speed. So, as soon as speed goes above 0 MPH, increased drag will reduce the overall efficiency.

In other words, go as slow as possible to get the best range (ignoring the fact that lights, power steering, radio, etc. will consume more power over the same distance travelled when average MPH goes down).
 

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I just drove and tested tonight.... 80mph 2.6miles/kwh, 75mph 2.8m/kwh , 70mph 3.0m/kwh , 65mph 3.2m/kwh. Maybe next time i'll hook up my ODBII reader and find the data product so I can make readings instead of estimates from the bar graph display. All these numbers were averaged over 5miles on flat land.
 

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Very good and helpful. Any chance that there is an (official) translator? I think I get the 4 levels of driving are low, middle, high, and very high. I can convert km to miles.

I just drove and tested tonight.... 80mph 2.6miles/kwh, 75mph 2.8m/kwh , 70mph 3.0m/kwh , 65mph 3.2m/kwh. Maybe next time i'll hook up my ODBII reader and find the data product so I can make readings instead of estimates from the bar graph display. All these numbers were averaged over 5miles on flat land.
This generally follows my performance on my first extended adventure from Houston to Austin (175 miles), although I think I had a bit more range efficiency.


On the way there at an average of about 75 mph for about 150 miles (@2.9 m/kwh) and about 25 miles in city driving (@5 m/kwh), I pulled up to DCFC charger with about 15 miles (estimating 3 kwh) of range remaining. By those calculations, I used 56.7 kwh, with 3.3 kwh in reserve. By the way, way to close for comfort, was glad to hit stop-and-go traffic through Austin.
On the way home, I left the same DCFC charger at 89% (say 54 kwh capacity), prepared to stop at another charger on the route. But driving home at 65 mph for about 170 miles (@3.6 m/kwh) and about 5 miles in city driving (@5 m/kwh) I made it home with about 25 miles (estimating 5 kwh) of range remaining (no stop needed). By those calculations, I used 48.2 kwh, with 5.8 kwh in reserve (starting with about 6 kwh depleted).


Small note, it is slightly uphill to Austin and downhill to Houston, so that would affect the range efficiency numbers slightly.
 

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Almost too easy ;-)

Geschwindigskeitprofil = Speed profile: Niedrig = Low, Mittel = Middel, Hoch = High, Sehr Hoch = Very High
Aussentemperature = Exterior Temperature: in deg C.
Heizuing / Kuhlung = Heating / Cooling: Aus = Off, An = On

They say the estimations are based upon test results obtained using the WLPT cycle.
 

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The chart Jurg linked is very nice, and "sehr hoch" seems to be just over 100km/hour in the driving cycle.... but my purpose was for trip planning and power budget. What I wanted to know (and did learn) was how many miles per kwh of electric at various speeds. For example, a relative lives 180 miles away. 48 miles is at 55mph (48/4=12kw), and the remaining miles are at 70mph (132/3=44kw)... can I make the trip? The answer is yes (56kw) , but only with 4kw to spare. In an ICE car, I get on the interstate sooner but the Bolt wouldn't make that journey due to increased consumption at 70mph.
 
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