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Regarding the range page...
85 kWh
Night
Highway
60 mph
32 F, Heat on
MSP
Calculator spits out 220. In flat land (read: much of Texas), I can see that in my car with heavy use of Cruise Control. Not in Seattle area though; flat land barely exists around here.
85 kWh
Night
Highway
60 mph
32 F, Heat on
MSP
Calculator spits out 220. In flat land (read: much of Texas), I can see that in my car with heavy use of Cruise Control. Not in Seattle area though; flat land barely exists around here.
I'm surprised that the smaller batteries seem significantly more efficient than the 85 kwh battery. They lose less range with increased speed and the 40 kwh battery does 4 miles/kwh at 55 whereas the 85 only does 3.5. The 85 kwh battery car has about 88% of the efficiency of the 40 kwh.
I wonder if that is battery efficiency or increased weight of the car.
I wonder if that is battery efficiency or increased weight of the car.
That's funny. My unspoken comment was that 90F wasn't hot enough. To cover Texas in July/August would like to see the scale at 110.
TonyWilliams
Active Member
A simple, safe rule of thumb is 1% increase in range per 1000 feet / 300 meters increase in density altitude above sea level.
So, 10,000 feet / 3000 meters would be about 10% increase in range. You can use this calculator to determine the density altitude:
Density Altitude Calculator - English/Metric
Effect of heavy RAIN on range
I see some of the modeling uses a small decrease in range for rain. Based on my expereince over the past two weeks, and in conversation with a Volt owner (who's daily commute is right at the 35-40 mile limit of his battery), I think heavy rain may be much more of a factor. I think it increases both rolling resistance (due to the fact that it increases surface area of contact and spray's off the back of the tire) AND resistance due to just pushing through the water.
Think about running in shallow water - or pushing something through water (like a boat, or even a shopping cart thru a puddle). Pushing the water out of the way takes a lot of power. Similarly, four large wheels pushing through even a moderately thin layer of water on the road probably increases the resistance/force significantly.
I commented above that I was seeing a range on the order of 180 miles (avg Wh/mi: 415-425) my first week driving in the cold (heater), rain (road resistance AND wiper motor), dark (lights), rush hour (a bit of stop/start and slow driving) and of course hills. The second week it has not been as rainy and i'm getting closer to 200 miles predicted range (for the standard charge) and the average Wh/Mi seems to be tracking closer to 390. The rest of the driving conditions have been similar. In daytime I get closer to 375 Wh/Mi.
I wanted to point this out - especially to the folks in CA who have had a lot of rain lately. I defninately would want to take a rain forecast into account if planning a max-range trip.
I see some of the modeling uses a small decrease in range for rain. Based on my expereince over the past two weeks, and in conversation with a Volt owner (who's daily commute is right at the 35-40 mile limit of his battery), I think heavy rain may be much more of a factor. I think it increases both rolling resistance (due to the fact that it increases surface area of contact and spray's off the back of the tire) AND resistance due to just pushing through the water.
Think about running in shallow water - or pushing something through water (like a boat, or even a shopping cart thru a puddle). Pushing the water out of the way takes a lot of power. Similarly, four large wheels pushing through even a moderately thin layer of water on the road probably increases the resistance/force significantly.
I commented above that I was seeing a range on the order of 180 miles (avg Wh/mi: 415-425) my first week driving in the cold (heater), rain (road resistance AND wiper motor), dark (lights), rush hour (a bit of stop/start and slow driving) and of course hills. The second week it has not been as rainy and i'm getting closer to 200 miles predicted range (for the standard charge) and the average Wh/Mi seems to be tracking closer to 390. The rest of the driving conditions have been similar. In daytime I get closer to 375 Wh/Mi.
I wanted to point this out - especially to the folks in CA who have had a lot of rain lately. I defninately would want to take a rain forecast into account if planning a max-range trip.
Another possibility is that the smaller battery cars have taller gearing in their transmissions, essentially trading off some acceleration for better energy efficiency. What would the range of the 85 kWh car be with the transmission of the 40 kWh version?
TonyWilliams
Active Member
An electric motor with a fixed gear ratio behaves completely differently from an ICE and gearbox in this respect. See the chart in this article. The efficiency map might be different for the Tesla motor, though.
Tesla has also made some other choices that reduce range, for example fitting fat 21 or 19 inch wheels. Narrower 17 inch wheels would have saved quite a bit of energy.
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The cells are identical. I'm not aware of any other difference between the various batteries than energy capacity and mass, but those are large differences. The power delivery capacity for a type of cell is often measured in C, where 1C is a discharge rate that will empty the battery in one hour. 1C current is equally taxing to all the battery variants, but for the 85 kWh battery, this is 85 kW (or close to that - it's actually measured in amperes, and kW will vary a bit with voltage), but for the 40 kWh variant 1C is only 40 kW. The 85 kWh battery is not only more than twice as large as the 40 kWh, but also more than twice as powerful.
More mass means that more energy is required to accelerate, and that rolling resistance is higher. You get more acceleration, but not quite double because you also have to accelerate the heavier battery, and the same goes for range. I think the largest battery weighs about 600 kg, and half of that is about 15% of the mass of the car, so it seems to fit reasonably well that the heavier car is only 88% as efficient as the lighter one.
On the other hand, those ranges assume constant speed, and then acceleration would not matter, only rolling resistance.
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Rolling resistance also increases with mass, the tire rubber is deformed more with higher vehicle weight. Rolling resistance - Wikipedia, the free encyclopedia
Rolling resistance and temperature: We had a very quick temperature drop here some days ago, it dropped from around 0 to -15 °C almost overnight. There is a section of road near me that I use to check rolling resistance, there is a small downhill leading into a couple of hundred meters of straight and almost level road. It continues to drop very, very slightly, such that speed should stay constant when I'm coasting if the brakes aren't dragging and tire pressure is correct. The speed limit is only 40 km/h, so aerodynamic drag is low and rolling resistance shows up well.
At 0 °C, my new Hakkapeliitta R tires roll so easily that the difference to summer tires is so small that I can't really say there's any difference at all, but at -15 °C speed dropped off noticeably.
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As eledille pointed out, rolling resistance goes up roughly linearly with weight and while inertia and kinetic energy do go up with mass, the mileage comparisons are at constant speed so there is no change in either that would require power.
I'm still wondering what would explain the differences between the batteries.
The old speed/range chart for the roadster lists tire rolling resistance as fairly constant 50-55 Wh/mile. I'm metric, so that's 32 Wh/km. Add a 75 kg driver and scale that for mass difference, and we get ((2100 + 75)/(1235 + 75))*32 = 53 Wh/km for Model S. Assume 10% higher rolling resistance due to insanely huge wheels, so I get around 60 Wh/km.
The effect of removing 300 kg would be (2175 - 300) / 2175 = 86% as much rolling resistance for the ligher vehicle. 60 * 0.86 = 52 Wh/km, so the difference would be about 8 Wh/km, or about 5% (480 km / 85 kWh = 177 Wh/km).
The effect of removing 300 kg would be (2175 - 300) / 2175 = 86% as much rolling resistance for the ligher vehicle. 60 * 0.86 = 52 Wh/km, so the difference would be about 8 Wh/km, or about 5% (480 km / 85 kWh = 177 Wh/km).
http://en.wikipedia.org/wiki/Rolling_resistance
Not if tire size is also increased commensurate with the load. The contact pressure is almost exactly equal to the air pressure so the tire tread compound is NOT deformed more. Actually, it may be deformed less if the tire has a larger overall diameter. Wikipedia is a very poor source for authoritative information. It's the reference of last resort because anyone can put any kind of drivel in it.
That's certainly true the Hakkapelitta R tires have very low rolling resistance.
As far as I know larger tires have greater rolling resistance?
Yes, I know. However, many of the more science oriented and uncontroversial articles are quite good. Also, I think the last few posts are about the efficiency difference between two cars that are identical except for mass and battery power (MS40 vs MS85).
I apologize for throwing wikipedia references at you, however. I didn't mean to be dismissive. Sorry.
According to the wikipedia article, though, rolling resistance depends on the rolling resistance coefficient C[sub]rr[/sub] multiplied by weight. The relationship is not linear despite seeming to be, because C[sub]rr[/sub] can depend on weight. In this case, though, where everything but mass and power is identical, I don't think it does.
BTW, I think maybe the efficiency difference between the MS variants issue should be moved to its own thread?
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We're talking about the same car with the same wheels and tires aren't we. In that case, the energy loss from the tires goes up linearly with loading for a reasonable range.
If you don't believe Wikipedia, how about NHTSA? Here's a reference to one of their papers on rolling resistance: http://deepblue.lib.umich.edu/bitstream/2027.42/4274/5/bac0913.0001.001.pdf
If you don't believe Wikipedia, how about NHTSA? Here's a reference to one of their papers on rolling resistance: http://deepblue.lib.umich.edu/bitstream/2027.42/4274/5/bac0913.0001.001.pdf
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