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stopcrazypp
Well-Known Member
He's not saying there is zero contribution, but that it is not that significant anymore. From the Roadster efficiency excel file, rolling resistance makes up 16% of overall energy consumption at 80mph, while the break even point between aero and rolling resistance is somewhere around 42-44mph.
http://www.teslamotorsclub.com/showthread.php/15550-Roadster-Efficiency-and-Range-Excel-File
For example for a 1750kg vs 1900kg, 8.6% more. Tesla's blog says there is a 1% increase in rolling resistance for a 1% increase in weight. That means the overall impact on range at 80mph is 8.6%*16% = 1.4% for that weight increase.
Let me show you my calculation with this data:
Weight= 1750 kg
Gravity= 9.81 m/s^2
Road friction coefficient for Model 3= 0.0153
constants to convert mph to m/s= 0.44704
air density= 1.2 kg/m^3 at sea level
frontal area=2.05 m^2
drag coefficient= 0.24
speed= 80mph
^2 means squared
Rolling Resistance Consumption = 1750 kg * 9.81 * 0.0153 * 0.447040 = 117.4 Wh/mi
Air Resistance Consumption = 0.44704*0.5*1.2*0.24*2.05*(80*0.44704)^2= 168.8 Wh/mi
Total consumption= 286.2 Wh/mi
Rolling Resistance Consumption is 117.4/286.2= 41.02% of total consumption. Rolling resistance consumption is independent of speed. It is the same at 1 mph or 100 mph. I will add more data.
There is a graph at the end of this page that shows how rolling resistance is the same at any speed. But I will add the formulas shortly.
http://images.thetruthaboutcars.com/2012/08/Model-S-range-Tables.pdf
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stopcrazypp
Well-Known Member
Maybe you should do a calculation for the Roadster using Tesla's data file, to see if it matches up, to check on your assumptions:
http://teslaflux.com/Efficiency.xls
This is from their blog entry from December 2008, so use the data on the 2008 Roadster (or early 2009 if 2008 can't be found):
http://www.teslamotors.com/blog/roadster-efficiency-and-range
Unfortunately they didn't have an excel file for the Model S, but they did post a chart on Wh/mi vs Roadster:
http://www.teslamotors.com/blog/model-s-efficiency-and-range
They say 400Wh/mi at 80mph for the Model S, 361Wh/mi at 80mph for Roadster.
Edit: I used your rolling resistance calculation, plugged in 1220 kg (2690lbs) for Roadster weight and got 81.9 Wh/mi. Tesla's chart for the Roadster only says 57.8 Wh/mi.
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I had a look at JB's excel file. It is different than what I use. It divides consumption into more categories and his air resistance is less than mine, but at the end the totals are similar. The formulas I use are well known physics equations. One of them is this one:
Drag force = 1/2 * air density * speed ^2 * drag-coefficient * frontal area
Source: Drag coefficient - Wikipedia, the free encyclopedia
For Roadster the data and the calculation would be like this:
Weight= 1335kg car + 82kg driver = 1417kg (82kg driver is from JB's blog here where he attached the excel file. Also source for car=1335kg)
Gravity= 9.81 m/s^2
Road friction coefficient for Roadster= 0.0153
constants to convert mph to m/s= 0.44704
air density= 1.2 kg/m^3 at sea level
frontal area= 2.086 m^2 source
drag coefficient= 0.35 source
speed= 80mph
Rolling Resistance Consumption = 1417 kg * 9.81 * 0.0153 * 0.447040 = 95.08 Wh/mi
Air Resistance Consumption = 0.44704*0.5*1.2*0.35*2.086*(80*0.44704)^2= 250.47 Wh/mi
Total: 345.55 Wh. JB's number is 361 Wh. It is a little different. He uses a different method. I'm sure for the Roadster his version is more accurate.
wallet said "weight shouldn't factor into it very much (if at all)". His comment is more accurate for the Roadster. Only 95 Wh/mi of 345 is from rolling resistance according to the same formula I use for Model S. However this is because the Roadster has a much worse 0.35 air drag coefficient because all the air intakes. Therefore I don't see any inconsistency here. For more information about Rolling Resistance Consumption, there is a simple website here. There are lots of other sources. Just search on Google.
I think the accuracy of these formulas is good and it is easy to test. I have now re-enabled the consumption calculator between superchargers. If somebody drives from one supercharger to another in the USA, they can test the accuracy. It integrates elevation and climate control. The page name is "Consumption Calculator". The file is here. I think now we can go back to Model 3 speculation.
Drag force = 1/2 * air density * speed ^2 * drag-coefficient * frontal area
Source: Drag coefficient - Wikipedia, the free encyclopedia
For Roadster the data and the calculation would be like this:
Weight= 1335kg car + 82kg driver = 1417kg (82kg driver is from JB's blog here where he attached the excel file. Also source for car=1335kg)
Gravity= 9.81 m/s^2
Road friction coefficient for Roadster= 0.0153
constants to convert mph to m/s= 0.44704
air density= 1.2 kg/m^3 at sea level
frontal area= 2.086 m^2 source
drag coefficient= 0.35 source
speed= 80mph
Rolling Resistance Consumption = 1417 kg * 9.81 * 0.0153 * 0.447040 = 95.08 Wh/mi
Air Resistance Consumption = 0.44704*0.5*1.2*0.35*2.086*(80*0.44704)^2= 250.47 Wh/mi
Total: 345.55 Wh. JB's number is 361 Wh. It is a little different. He uses a different method. I'm sure for the Roadster his version is more accurate.
wallet said "weight shouldn't factor into it very much (if at all)". His comment is more accurate for the Roadster. Only 95 Wh/mi of 345 is from rolling resistance according to the same formula I use for Model S. However this is because the Roadster has a much worse 0.35 air drag coefficient because all the air intakes. Therefore I don't see any inconsistency here. For more information about Rolling Resistance Consumption, there is a simple website here. There are lots of other sources. Just search on Google.
I think the accuracy of these formulas is good and it is easy to test. I have now re-enabled the consumption calculator between superchargers. If somebody drives from one supercharger to another in the USA, they can test the accuracy. It integrates elevation and climate control. The page name is "Consumption Calculator". The file is here. I think now we can go back to Model 3 speculation.
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EVNow
Well-Known Member
Cool.
Using realistic figures - Frontal Area same as BMW 3 (2.16), CD of 0.26, 60 kWh, 1750 lb @ 60 mph I get 229 miles. @ 70 mph I get 196 miles.
I have now clarified that weight is in kg. This is weight data for Model S from wikipedia:
1,961 kg (4,323 lb) (S60)
2,085 kg (4,597 lb) (S60D)
2,090 kg (4,608 lb) (S70D)
2,108 kg (4,647 lb) (S85)
2,188 kg (4,824 lb) (S85D)
2,239 kg (4,936 lb) (P85D)
Model S 60 is 1961 kg with 60 kWh pack. Model 3 with 60 kWh pack should be less. How much less? You will decide on that. 10% less is 1765kg, 15% less is 1667kg, 20%less is 1569kg. Weight estimations so far are too pessimistic.
Here is my guess:
Base model, Model 3:
battery: 60 kWh
frontal area: 2.16 m^2
Drag Coefficient: 0.26
Weight of car (kg): 1650 kg
EPA rating: 225 mi
Long range version Model 3:
battery: 80 kWh
frontal area: 2.16 m^2
Drag Coefficient: 0.26
Weight of car (kg): 1790 kg
EPA rating: 289 mi
1,961 kg (4,323 lb) (S60)
2,085 kg (4,597 lb) (S60D)
2,090 kg (4,608 lb) (S70D)
2,108 kg (4,647 lb) (S85)
2,188 kg (4,824 lb) (S85D)
2,239 kg (4,936 lb) (P85D)
Model S 60 is 1961 kg with 60 kWh pack. Model 3 with 60 kWh pack should be less. How much less? You will decide on that. 10% less is 1765kg, 15% less is 1667kg, 20%less is 1569kg. Weight estimations so far are too pessimistic.
Here is my guess:
Base model, Model 3:
battery: 60 kWh
frontal area: 2.16 m^2
Drag Coefficient: 0.26
Weight of car (kg): 1650 kg
EPA rating: 225 mi
Long range version Model 3:
battery: 80 kWh
frontal area: 2.16 m^2
Drag Coefficient: 0.26
Weight of car (kg): 1790 kg
EPA rating: 289 mi
stopcrazypp
Well-Known Member
By using a higher weight number you get an even bigger discrepancy for rolling resistance. Again, I used the 2690lb number which was the quoted number for a 2008-2009 Roadster; keep in mind that JB's blog article came out in 2008 so you can't use 2015 numbers.
In case it is not clear, JB's excel file has all the categories listed and the blog explains each of them. tire = rolling resistance, aero = air resistance, ancillary = accessory load, drivetrain = battery/inverter/motor conversion losses. All I'm saying is given the huge discrepancy between the tire and aero numbers JB is pointing out, you may well want to check the different constants you are using to make sure they are correct.
The accuracy of this spreadsheet was tested with lots of (over 50) actual trip data. The accuracy is very good. There is no error. If you don't believe me you can test it yourself the next time you drive from one supercharger to another. Open the file here, switch to page "Consumption Calculator", select the two superchargers. It will tell you how much kWh energy you will consume, what your Wh/mi number will be and how many rated miles you will consume. The calculations done here are more detailed than EVtripplanner.
ryanjm
Tesla Podcast Host
Thank you once more
Ps: would not TM3 come with smaller wheels then 19"?
I'm purely guessing, of course, but I'm expecting 17" wheels on the base models, and an optional 19".
One thing is that TM3 will be relatively heavy and will need a bit bigger contact patch not to destroy tires prematurely.
One way of increasing contact patch is by increasing width of the tire, the other is by increasing total wheel diameter.
First way also increases aero-drag while the second does not. I'd guess TM3 will have 18" base setup, with 225/55 tires.
One way of increasing contact patch is by increasing width of the tire, the other is by increasing total wheel diameter.
First way also increases aero-drag while the second does not. I'd guess TM3 will have 18" base setup, with 225/55 tires.
Well the way I see it is that, currently a range upgrade of 70Kwh battery is offered to Roadster. I'm pretty sure Model 3 would easily fit that battery pack if not even more. Considering the car is at least 3 years away from production, the battery pack size and storage density can be improved till the release date. so 300+ mile is a possibility. But do not expect the base edition to have it. The only question mark for me would be, if Tesla would want such a range on model 3 to compete with Model S sales.
I am not sure why this agrument keeps coming up.... Why does the Model S need to be superior in every way to the Model 3 ? They are completely different cars with different purposes. Is the BMW 3/4 Series slower the the 5 or 7 ? Different cars for different purposes with different specs.
stopcrazypp
Well-Known Member
I think it comes from the German automakers limiting their lower end models. For example M5 tends to be faster than the M3 and E63 faster than C63. Tesla however, doesn't necessarily have to follow that convention.
Really BMW says M3 is 0-60 in 3.9 and the M5 is 4.2 at least in the USA
M6 is 4.1 sec
MassModel3
Member
Absolutely they would.
The Model 3 and Model S are, and forever will be, two very different classes of vehicle. They're not going to cripple the 3 just to make sure that the S version of everything is always better. The Roadster, the S, and the X were/are all meant to be money makers designed to finance the 3. The 3 is the original goal and it won't be held back by Tesla for fear of being as good as, or better than, the S in range (or anything else).
stopcrazypp
Well-Known Member
I believe that may be do with the generation discrepancy. The F10 M5 is quoted officially at 4.2 (Motor Trend got 3.7) and I believe the E90 M3 is quoted at at 4.7 (Motor Trend got 4.2 for coupe). The F80 M3 is quoted at 3.9 /4.1 (Motor Trend got 3.8), but I believe the F10 numbers are due for an update (2017 m5 is being planned).
ProphetM
Member
The Model S is not static. I fully expect that they will continue to work battery advances into the S when possible. By the time the 3 comes out, the S might have a 100 or 110 Kwh pack.
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