I'd think it'd be higher due to the larger mass of the car.It will be interesting to see the kilowatt-hour per mile data on the Model S when it is available, but I'll bet it is similar to the Roadster.
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I'd think it'd be higher due to the larger mass of the car.It will be interesting to see the kilowatt-hour per mile data on the Model S when it is available, but I'll bet it is similar to the Roadster.
It's about 20% higher for the Model S.
It's a simple calculation but I've also seen it somewhere... can't find it now. On Tesla's web site they recommend sizing your solar panel array for 300 wh per mile for the Model S. If you take the battery size compared to the range you get between 250 and 283 wh/mi depending on which pack you choose. For the Roadster the same calculation reveals 216 wh/mi. If you pick the mid sized 60kwh battery it represents a 20.6% increase over the Roadster. Tesla has stated the new charger is very slightly more efficient than the Roadster's so you can conclude the Model S consumes about 20% more power than the Roadster per mile.Thanks for the information. Can you tell us the source of your information?
Larry
It's a simple calculation but I've also seen it somewhere... can't find it now. On Tesla's web site they recommend sizing your solar panel array for 300 wh per mile for the Model S. If you take the battery size compared to the range you get between 250 and 283 wh/mi depending on which pack you choose. For the Roadster the same calculation reveals 216 wh/mi. If you pick the mid sized 60kwh battery it represents a 20.6% increase over the Roadster. Tesla has stated the new charger is very slightly more efficient than the Roadster's so you can conclude the Model S consumes about 20% more power than the Roadster per mile.
In reality the difference will probably depend on driving patterns and apparently pack size. Since the S has a lower coefficient of drag, it will conceivably perform closer to Roadster numbers at highway speeds like 70 mph (115 km/hr). When you're driving in stop-and-go traffic, the light weight of the Roadster will help it perform much better than the S.
I'd think it'd be higher due to the larger mass of the car.
I think it would be more due to the larger aerodynamic cross-section. Even if the car is slipperier, it's' still BIGGER.
I've figured the CdA by taking the dimensions and images from web site and calculated how much area the silhouette took.
W x H xpercent area of silhouette x Cd = CdA
77.3" x 56.5" x .81 x .225 = 5.53 Model S
72.9" x 44.35" x .8 x .35 = 6.29 Roadster
Again I'm not claiming that the power drain of the Model S would be less than a Roadster, just that it might not be significantly greater when considering aerodynamics and improved battery chemistry, particularly at high speeds.
Larry
Curious... if that's really true, there might be less of a penalty for going above 55 mph...?
Hi Doug,
...my thinking is that at high speeds the power drain would of course increase exponentially in both cases, but the Model S's better aerodynamics would start to narrow the power drain in comparison with the Roadster whose power drain would increase even faster than the Model S.
Larry
Mass makes a difference when you're changing speed or elevation, because both kinetic and gravitational potential energy are linear in speed. At a steady speed on a flat road, it just doesn't matter, so you'd expect that the car with the better CdA would have lower energy use per mile (assuming no differences in the rest of the system like the efficiency of the power train, the tires, etc.) The higher the speed, the more energy/mile is used to overcome drag so the greater advantage the lower CdA car would have. (BTW, drag energy per mile increases quadratically in speed, not exponentially.)
Mass makes a difference when you're changing speed or elevation, because both kinetic and gravitational potential energy are linear in speed. At a steady speed on a flat road, it just doesn't matter, so you'd expect that the car with the better CdA would have lower energy use per mile (assuming no differences in the rest of the system like the efficiency of the power train, the tires, etc.) The higher the speed, the more energy/mile is used to overcome drag so the greater advantage the lower CdA car would have. (BTW, drag energy per mile increases quadratically in speed, not exponentially.)
That is, I'd expect that if you were crusising through the flat desert at 80 mph that the S would use less energy for the same distance than the Roadster, possibly by a pretty large margin. Getting to speed and climing hills would be worse, though, and real driving nearly always involves that.
Friction on the tire depends on the mass. So 2 cars with same CdA, but different masses will spend different amount of energy cruising at a steady speed on a flat road.Mass makes a difference when you're changing speed or elevation, because both kinetic and gravitational potential energy are linear in speed. At a steady speed on a flat road, it just doesn't matter, so you'd expect that the car with the better CdA would have lower energy use per mile (assuming no differences in the rest of the system like the efficiency of the power train, the tires, etc.)
If you're talking about me,Daniel, I have a feeling I'll be driving the Tesla significantly more aggressively than the Prius. With electricity cost so small compared to gas, the range more than enough for me to "play" with, and the available torque I forsee taking the highway more often and probably exceeding the speed limit a bit more as well. May employ some hypermiling techniques from time to time just for fun, but one advantage is using zero gas and not having to think about technique.I'm surprised that the Roadster, which is so low to the ground, has a higher CdA than the much larger Model S. Oh, well, I believe you folks. I'm just surprised.
Now when we talk about efficiency, are we talking about the same driving profile for both cars? Or are we talking about driving each car as each was intended to be driven? A sporty sedan vs a high-performance sports car! I know someone over on Prius Chat who is an early Model S reservation holder and is a high-mpg Prius driver. I expect him to drive his Model S in such a way as to maximize range and efficiency. I like to feel the thrust, and I drive my Roadster pretty hard. Comparing his Model S to my Roadster is a real apples-to-oranges comparison.
I'm surprised that the Roadster, which is so low to the ground, has a higher CdA than the much larger Model S. Oh, well, I believe you folks. I'm just surprised.
Now when we talk about efficiency, are we talking about the same driving profile for both cars?
Coming over to the dark side, eh, Evan?If you're talking about me,Daniel, I have a feeling I'll be driving the Tesla significantly more aggressively than the Prius. With electricity cost so small compared to gas, the range more than enough for me to "play" with, and the available torque I forsee taking the highway more often and probably exceeding the speed limit a bit more as well. May employ some hypermiling techniques from time to time just for fun, but one advantage is using zero gas and not having to think about technique.
Thanks. Larry.Hi Daniel,
To put this in context perhaps it would be useful to see where the discussion started. Initially I was commenting in the Carbon footprint clarification thread stating that Roadsters would produce better results than the Leaf that was used in the subject study. The moderators started this new thread when discussion veered to discuss efficiency comparisons between the Model S and Roadster.
Anyway, to answer your question I was discussing efficiency as quantified by the watt-hr/mi characteristics of the respective vehicles. The subject U.C.S. study used 340 watt-hr/mi for the Leaf. From Tesla's published watt-hr/mile vs. speed graph for the Roadster I was able to estimate that at 55 mph the Roadster would draw about 230 watt-hr/mile.
A similar chart for the Model S would be helpful in addressing our comparisons because it would incorporate all of the factors, weight, rolling resistance, aerodynamics, etc., in one aggregate efficiency number at various speeds.
Larry
A similar chart for the Model S would be helpful in addressing our comparisons because it would incorporate all of the factors, weight, rolling resistance, aerodynamics, etc., in one aggregate efficiency number at various speeds.
Thanks. Larry.
Is that figure for the Roadster Wh from the battery, or from the wall? From the wall, I think I burn a lot more Wh, but then I've never measured at 55 mph. On the freeway I drive the limit (70 mph outside of town here) and in town I accelerate hard up to the speed limit for the road I'm on unless there's a car in front of me. My point was that this is a high-performance sports car, and even though it can be driven 55 for range, it was built to do so much more.
I never drive the Prius 70 mph. For one thing, it doesn't feel safe. The Roadster feels really solid. And for another, like Evan, I'm more concerned about fuel when I'm burning foreign gasoline than when I'm burning locally-made water-derived electrons. (Washington state = water power.) And the Prius is a car that says "I'm efficient," whereas the Roadster is a car that says "I'm a hot-rod."