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WH/mile?
- Thread starter Raiders83
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geordi
Mr Fusion V.1
PCMC's experiment above is interesting to me, very cool. It also seems to mirror real-world experience right now. I'm on another road trip, this time to the West Coast. I've got a trailer hitch tray on the back with 4 tool boxes that hide just inside the sides (so the lights are visible of course) and maybe about 2-3 inches above the lip of the spoiler. They shouldn't be adding much to the wind resistance. About 250 lbs maybe in total with the tray. It has been VERY hot though - temperatures above 90 every day and in North Texas (Dallas) it was 106 for the days I was there. Car camping again, and road speeds of 80-85 normally, now that I'm west of Kansas.... Road speeds of 90-100.
Observed numbers then:
80mph, getting about 340 wh/mi
85mph, 370~
90-95mph, 400~
100mph, 433! That's not bad at all, although the wind changed and a crosswind made it closer to 500. This was between Salt Lake City and the Bonneville Salt Flats, so dead flat and straight for 50 miles or so.
But the best.... I challenge anyone to beat this: From Donner Pass down to Sacramento, road speed consistent at 80mph... I used just TWO miles of range and the wh/mi was as low as 144!!! Of course that was 60 miles all downhill, so yeah that helped a lot.
Observed numbers then:
80mph, getting about 340 wh/mi
85mph, 370~
90-95mph, 400~
100mph, 433! That's not bad at all, although the wind changed and a crosswind made it closer to 500. This was between Salt Lake City and the Bonneville Salt Flats, so dead flat and straight for 50 miles or so.
But the best.... I challenge anyone to beat this: From Donner Pass down to Sacramento, road speed consistent at 80mph... I used just TWO miles of range and the wh/mi was as low as 144!!! Of course that was 60 miles all downhill, so yeah that helped a lot.
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@geordi - The key thing the Wh/mi numbers you posted demonstrate is the impact of vehicle speed. Energy loss due to aerodynamic drag is proportional to velocity squared. Increasing speed from 80 mph to 100 mph and you'd expect your aerodynamic drag increase by about 55%, (100/80)*2. Now your numbers do not show that high of an increase, but not all the energy use in aerodynamic drag. There are some other terms such as rolling resistance, HVAC load, etc., which do not increase by speed squared.
As the old saying goes, speed kills!
As the old saying goes, speed kills!
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geordi
Mr Fusion V.1
You have a math error there - squaring something multiplies it by itself, not by two. For your math there, that would result in 1.25 times 1.25, for 1.56.
So going from 8mph to 64mph, the wind resistance doubles. Or from 9 to 81. Or from 10 to 100.... But while it is certainly more, it isn't 50% greater from 81 to 100.
That's why the wh/mi didn't increase by the same proportions. Obviously more power is needed to counter faster travel, but no, that platitude of "speed kills" doesn't really apply here. I had a 4x6 V-nose enclosed trailer (about 6 feet tall) behind this same car before this trip, and in Florida (very hot and very flat) at 65mph.... I was pulling 600 wh/mi. That's ENTIRELY about the wind resistance. The only thing I haven't confirmed for myself yet is whether these boxes on the back are costing me increased power used, or if it is simply external conditions and higher speeds.
As a function of charging times and arrival battery, the higher speeds seem to only reduce the arrival battery by about 3% from originally-predicted numbers, and add about 5 minutes to charging times. For a day of 800 miles from Wyoming to California.... Spending considerably less time out on the road but at higher speeds is a worthy trade. Is it more efficient? No, of course not. But time is irreplaceable, everything else is.
So going from 8mph to 64mph, the wind resistance doubles. Or from 9 to 81. Or from 10 to 100.... But while it is certainly more, it isn't 50% greater from 81 to 100.
That's why the wh/mi didn't increase by the same proportions. Obviously more power is needed to counter faster travel, but no, that platitude of "speed kills" doesn't really apply here. I had a 4x6 V-nose enclosed trailer (about 6 feet tall) behind this same car before this trip, and in Florida (very hot and very flat) at 65mph.... I was pulling 600 wh/mi. That's ENTIRELY about the wind resistance. The only thing I haven't confirmed for myself yet is whether these boxes on the back are costing me increased power used, or if it is simply external conditions and higher speeds.
As a function of charging times and arrival battery, the higher speeds seem to only reduce the arrival battery by about 3% from originally-predicted numbers, and add about 5 minutes to charging times. For a day of 800 miles from Wyoming to California.... Spending considerably less time out on the road but at higher speeds is a worthy trade. Is it more efficient? No, of course not. But time is irreplaceable, everything else is.
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Tires are the hidden cost of quick EVs. I figured it up earlier I was spending more on tires than I was electron juice per mile.
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Pavement and winds make a big difference too. When I turn onto FM2678 at Refugio going to Corpus, that terrible pavement makes my wh/mi skyrocket by like 25% compared to what it was on US 77 before. One thing to check is the state of your tires. Under inflated tires can be a huge drag. In fact, slightly over inflating compared to the numbers in the door jamb can boost range, at the expense of ride quality and uneven wear.
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@geordi - aerodynamic drag is a function of velocity squared. So you are correct, in should have typed bny values as (100/80)**2 or (100/80)^2 depending upon which symbology you prefer.
So (100/80) **2 = (100/80)^2 = (100/80)*(100/80) = 1.25 * 1.25 = 1.5625, so a 50% increase.
I agree your numbers do not go up by 50%, and that is because there are some components of the total energy consumption that come from other sources that are not related to the square of velocity, but increased speed is a major factor in increased energy consumption due to basic aerodynamic.
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geordi
Mr Fusion V.1
Found a couple articles that help sort this into easily calculated results
Drag Equation Calculator for the calculator
https://www.tesla.com/sites/default/files/blog_attachments/the-slipperiest-car-on-the-road.pdf has some numbers from the wind tunnel of the Model S.
Now the calculator (and the math) requires a couple other things, so here's the numbers I used:
Air density: 1.1644 kg/m^3 for air at sea level and 30 degrees C (86 F)
Velocity: Various, mph
Drag coefficient: 0.24 per Tesla information for the Model S
Area: This one I had to massage, because the PDF's number of 77 lbs at 70mph did NOT work at their stated 25.2 square feet, but worked if it was increased to 27 square feet.
At that point, the calculated wind pressure at 70mph is 77 lbs, 80 is 100lbs, and 100mph is 157 lbs. That's not nothing, but it also doesn't feel like a huge thing when you are talking about throwing a 5000 lb car through the wind at such (comparatively) low speeds versus pushing an airplane through the air at 600 mph.
Drag Equation Calculator for the calculator
https://www.tesla.com/sites/default/files/blog_attachments/the-slipperiest-car-on-the-road.pdf has some numbers from the wind tunnel of the Model S.
Now the calculator (and the math) requires a couple other things, so here's the numbers I used:
Air density: 1.1644 kg/m^3 for air at sea level and 30 degrees C (86 F)
Velocity: Various, mph
Drag coefficient: 0.24 per Tesla information for the Model S
Area: This one I had to massage, because the PDF's number of 77 lbs at 70mph did NOT work at their stated 25.2 square feet, but worked if it was increased to 27 square feet.
At that point, the calculated wind pressure at 70mph is 77 lbs, 80 is 100lbs, and 100mph is 157 lbs. That's not nothing, but it also doesn't feel like a huge thing when you are talking about throwing a 5000 lb car through the wind at such (comparatively) low speeds versus pushing an airplane through the air at 600 mph.
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I want to thank everyone who is providing their Wh/mi, model, and driving conditions. This really is helping me understand! And a really big thank you to @geordi and @PCMc for your thorough feedback. I really appreciate the equations, too!
It's still surprising to me how variable an electric car's efficiency can be. I got my model 3 after WonderCar, my 1992 Honda Civic was murdered by a hit and run driver. He was my best (non-human, non-canine) friend. I cried for weeks. At the time of his demise, he had over 150,000 miles on a rebuilt engine, and with the way I normally drive, which is always at least 10% over the speed limit, he got ~32 mpg. At worst he got ~26 mpg when the AC was maximum. His tank was small enough that a fill-up occurred every 10 gallons. So I could get a range of at least 260 miles, but usually 320. That's not much variability compared to the numbers @geordi and others are reporting here.
I know these are entirely different engines and power sources, but the comparison: which engine is more economical and environmental (assuming gas as the source of electric power), an electric car that averages 400 Wh/mi is getting pretty close to even, right?
It's still surprising to me how variable an electric car's efficiency can be. I got my model 3 after WonderCar, my 1992 Honda Civic was murdered by a hit and run driver. He was my best (non-human, non-canine) friend. I cried for weeks. At the time of his demise, he had over 150,000 miles on a rebuilt engine, and with the way I normally drive, which is always at least 10% over the speed limit, he got ~32 mpg. At worst he got ~26 mpg when the AC was maximum. His tank was small enough that a fill-up occurred every 10 gallons. So I could get a range of at least 260 miles, but usually 320. That's not much variability compared to the numbers @geordi and others are reporting here.
I know these are entirely different engines and power sources, but the comparison: which engine is more economical and environmental (assuming gas as the source of electric power), an electric car that averages 400 Wh/mi is getting pretty close to even, right?
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@Gkram - regarding your comments regarding how variable an electric cars efficiency can be and efficiency comparisons, without getting overly bogged done in gory details, here's one relatively simply to compare that actual energy efficiency.
This all is based upon looking at what the total energy content in a gallon of gasoline versus other energy sources. One good resource that helps provide some substance without getting too deep is data published by the Alternative Fuel Data Center.
They use a unit of GGE, or Gasoline Gallon Equivalent to equate what the energy content is for different fuel sources. GGE for gasoline is naturally 1.00, versus say pure ethanol at about 0.67 GCE (1 gal of ethanol equivalent of 0.67 gallons of gas) or 1 kWh of electricity being only 0.03 GGE, or it takes about 33 kWh of electricity to provide the same energy content of 1 gallon gasoline.
So for you example of a vehicle getting 32 mpg, flip that over and it's your consume 0.03125 gallon of fuel per mile traveled. Now if your use the 1 kWh = 0.03 GGE, what that say is that your 32 mpg vehicle is running at an equivalent consumption of (0.03125 gal/mile) / (0.03 GGE/kWh) = 1.042 kWh/mile, or in the units you're used to for your Model 3, a whopping 1,042 Wh/mi. Now do the number for your 26 mpg case and you'll end up at 0.0385 gal/mile which again at 0.03 GGE/kWh, you're at 1,282 Wh/mi!
Another way to look at this is the conditions which take your 32 mpg car to run at 26 mpg, is the equivalent of an increase of 240 Wh/mi. So while you may not feel like your MPG is changing as much as what your EV changes, that a false perception masked by the fact that about 2/3rds of the energy in your total consumed gasoline is going to waste heat and not actually doing anything to move your car. But when you look at the absolute magnitude of the energy increase you'll see it's actually not any different than your EV on the impact of vehicle speed or temperature driving higher HVAC energy use.
Or if you run the numbers in the other direction, your 400 Wh/mi consumption for an EV works out to be about 83 mpg equivalent energy use.
.... here's the general math ... 400 Wh/mi = 0.4 kWh/mi = 0.012 GGE/mile --> 1/0.012 = 83.3 mile/GGE or 83.3 MPGe (equivalent)
This all is based upon looking at what the total energy content in a gallon of gasoline versus other energy sources. One good resource that helps provide some substance without getting too deep is data published by the Alternative Fuel Data Center.
They use a unit of GGE, or Gasoline Gallon Equivalent to equate what the energy content is for different fuel sources. GGE for gasoline is naturally 1.00, versus say pure ethanol at about 0.67 GCE (1 gal of ethanol equivalent of 0.67 gallons of gas) or 1 kWh of electricity being only 0.03 GGE, or it takes about 33 kWh of electricity to provide the same energy content of 1 gallon gasoline.
So for you example of a vehicle getting 32 mpg, flip that over and it's your consume 0.03125 gallon of fuel per mile traveled. Now if your use the 1 kWh = 0.03 GGE, what that say is that your 32 mpg vehicle is running at an equivalent consumption of (0.03125 gal/mile) / (0.03 GGE/kWh) = 1.042 kWh/mile, or in the units you're used to for your Model 3, a whopping 1,042 Wh/mi. Now do the number for your 26 mpg case and you'll end up at 0.0385 gal/mile which again at 0.03 GGE/kWh, you're at 1,282 Wh/mi!
Another way to look at this is the conditions which take your 32 mpg car to run at 26 mpg, is the equivalent of an increase of 240 Wh/mi. So while you may not feel like your MPG is changing as much as what your EV changes, that a false perception masked by the fact that about 2/3rds of the energy in your total consumed gasoline is going to waste heat and not actually doing anything to move your car. But when you look at the absolute magnitude of the energy increase you'll see it's actually not any different than your EV on the impact of vehicle speed or temperature driving higher HVAC energy use.
Or if you run the numbers in the other direction, your 400 Wh/mi consumption for an EV works out to be about 83 mpg equivalent energy use.
.... here's the general math ... 400 Wh/mi = 0.4 kWh/mi = 0.012 GGE/mile --> 1/0.012 = 83.3 mile/GGE or 83.3 MPGe (equivalent)
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^ great post. Would make an interesting spreadsheet for many people to use and get a better idea of comparing ICE to BEVs. Great way of explaining to others who don't realize how much energy really is in a gallon of gasoline. It also why I abhor using E85. I get less energy content so even though E85 is cheaper, my fuel consumption goes up. OTOH when using very high performant forced induction ICE vehicles, I can get more power out of them by increasing boost and in that situation I don't care so much about fuel consumption as I do performance.
I think the thing most people forget about with ICE is all the heat that is wasted. On the flip side, in the cold, the ICE cars definitely close the gap a lot. Especially if they are not using something like a heat pump which has its limits in really cold weather anyway.
Another thing I have seen mentioned here is the amount of power required by a speed increase. While drag goes up by the square of speed, power required goes up by the cube of speed. These are general statements and don't always work out exactly that way but good for back of the napkin measurements. Here is one of the best, concise, and relatively easy to understand explanations I've seen. I wish I had read it when I first started school to become an aeronautical engineer. It is an interesting read even for the less geeky people. Once you get past setting the stage about fluids and drag in general, it is a fun read.
physics.info
I think the thing most people forget about with ICE is all the heat that is wasted. On the flip side, in the cold, the ICE cars definitely close the gap a lot. Especially if they are not using something like a heat pump which has its limits in really cold weather anyway.
Another thing I have seen mentioned here is the amount of power required by a speed increase. While drag goes up by the square of speed, power required goes up by the cube of speed. These are general statements and don't always work out exactly that way but good for back of the napkin measurements. Here is one of the best, concise, and relatively easy to understand explanations I've seen. I wish I had read it when I first started school to become an aeronautical engineer. It is an interesting read even for the less geeky people. Once you get past setting the stage about fluids and drag in general, it is a fun read.
Aerodynamic Drag – The Physics Hypertextbook
Drag is the friction from fluids like air and water. A runner feels the force of aerodynamic drag. A swimmer feels the force of hydrodynamic drag.
physics.info
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as other said it depends on how and where you drive. but to me 350 seems high.
In FL, plaid gets around 330-340 on highway (I do orlando-Miami) once a month and it is consistent at the range at 75-80MPH. in the city when I commute to work/school ..etc I see it average 270-280.
Try to check tires, alignment, brake pads any issues will cause the car to work more and could explain your high usage.
In FL, plaid gets around 330-340 on highway (I do orlando-Miami) once a month and it is consistent at the range at 75-80MPH. in the city when I commute to work/school ..etc I see it average 270-280.
Try to check tires, alignment, brake pads any issues will cause the car to work more and could explain your high usage.
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Wol747
Active Member
Of course these numbers are interesting from the personal point of view, but digging deeper environmentally-wise we have to look at the total energy used to produce and deliver a gallon/Kwh to the consumer. Digging really right down to the bottom all the energy building the plant etc and its useful lifetime.
That’s the sort of number that the brighter deniers (oxymoron?) bring up and it’s in the “how long is a piece of string” category.
That’s the sort of number that the brighter deniers (oxymoron?) bring up and it’s in the “how long is a piece of string” category.
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geordi
Mr Fusion V.1
Crossing Nebraska today heading Eastbound, I had multiple confirmations that I was pushing into a headwind of some substance.
Drafting behind a large F150 at 95mph for an extended period, the average Wh/mi was ~354. Very agreeable considering the wind that he was pushing out of my way. We had to slow for traffic for another extended period and at 77mph, the Wh/mi dropped to 337.
I have also repositioned the cases on the back of the car to be closer to the center and now only about 1" above the spoiler, and shifted them forward (closer to the rear door) so that they should be even further out of the wind.
Drafting behind a large F150 at 95mph for an extended period, the average Wh/mi was ~354. Very agreeable considering the wind that he was pushing out of my way. We had to slow for traffic for another extended period and at 77mph, the Wh/mi dropped to 337.
I have also repositioned the cases on the back of the car to be closer to the center and now only about 1" above the spoiler, and shifted them forward (closer to the rear door) so that they should be even further out of the wind.
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I have put about 1600 miles on my 2020 Model S Performance since buying it.
Here is the car:
Here is the car:
- 2020 Model S Performance
- 19" tempest wheels with stock sized Goodyear RS-A2
- Aero hubcaps in place
- Lowered about 2/3 inch front and back with Blox lowering links
- I always drive in sport mode for acceleration, but other than a handful of crazy take-offs to give my daughter a giggle, I generally drive conservatively around town. On highway, I do 75-80 as most highways in Texas near me are 75 mph speed limit.
- Ceramic tint all around to reduce heat in cabin and shade under the fixed glass roof.
- Average across the 1600 miles with combined cycle: 305 wh/mile
- Average on two 500-mile road trips: 288-295 wh/mi. This includes about 100 miles of local driving (20%) and rest highway (80%) doing 75-80 on highway.
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geordi
Mr Fusion V.1
DO NOT PUSH IT TO ZERO!!! That's really asking to be walking and have a damaged battery. Once you are below 20% the car is not supporting the 12v battery any longer, and if BOTH are drained, even being dropped off by a tow truck at a supercharger won't get you back from being bricked.
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