Efficiency comparison - Model S v. Roadster

[daniel]

^ Okay. Got it. Thanks.

[Norbert]

Anyone tried to compare our calculated 65 mph numbers with the Tesla-store-big-screen-range-calculator numbers? It seems those are better than our calculations, although I wouldn't know if those numbers were obtained with parameters which would give exactly 300 miles for 55 mph.

[Doug_G]

Anyone tried to compare our calculated 65 mph numbers with the Tesla-store-big-screen-range-calculator numbers? It seems those are better than our calculations, although I wouldn't know if those numbers were obtained with parameters which would give exactly 300 miles for 55 mph.

Someone should go equipped with a pad of paper and write down the calculated range estimate at every 5 mph. Then the curves can be tweaked until they match, and that should give better estimates of various parameters.

[hcsharp]

...
These efficiency calculations by our forum members seem to demonstrate that even though a Model S is less efficient than a Roadster it is only in the range of 10% - 13% less efficient and therefore it would be very difficult to find an ICE vehicle that would produce less CO2 than a Model S even in dirty electricity regions of the country.

Where do you get the idea it's only 10 - 13% less efficient? Using raw mileage per kwh reveals the 85 kwh model S to be 23% less efficient than the Roadster (equivalent to consuming 31% more power per mile than the Roadster). And the 60 kwh model is 17% less efficient (which is the same as consuming 20.5% more power per mile). The spread slims a bit when you go faster. But even de-rating the capacity to 82kwh doesn't get you to 10 - 13%. Are you assuming there will be large charging efficiency gains?

[Larry Chanin]

Where do you get the idea it's only 10 - 13% less efficient?

Posting #23 using rabar10's numbers for the Model S with different aero multipliers and published efficiency for the Roadster at 55 mph.

Larry

[hcsharp]

Posting #23 using rabar10's numbers for the Model S with different aero multipliers and published efficiency for the Roadster at 55 mph.

Larry

Correct me if I'm wrong but I think you made some wrong assumptions in that post. It's my understanding that the Roadster's published rating is 216 wh/mi at 55 mph, not 230. And the Model S ratings determined from simple math reveal 250 wh/mi for the 40 kwh pack; 261wh/mi for the 60 kwh pack; and 283 wh/mi for the 85 kwh pack.

[Larry Chanin]

Correct me if I'm wrong but I think you made some wrong assumptions in that post. It's my understanding that the Roadster's published rating is 216 wh/mi at 55 mph, not 230. And the Model S ratings determined from simple math reveal 250 wh/mi for the 40 kwh pack; 261wh/mi for the 60 kwh pack; and 283 wh/mi for the 85 kwh pack.

I was referring to the Wh/mi value at 55 mph off of this curve.



Or interpolated from this data file:

https://www.teslamotors.com/display_...me=range_table

For the Model S values I used the estimated range that rabar10 posted in posting #22, dividing the pack kW by estimated range.

This looks consistent with daxz's graph in posting #25.

Larry

[hcsharp]

I was referring to the Wh/mi value at 55 mph off of this curve.

Or interpolated from this data file:

https://www.teslamotors.com/display_...me=range_table

For the Model S values I used the estimated range that rabar10 posted in posting #22, dividing the pack kW by estimated range.

This looks consistent with daxz's graph in posting #25.

Larry

Has Tesla given any word as to how they came up with the range for each battery size? I've heard people say "range at 55mph" but they use the same language "range at 55 mph" to describe the Roadster's range of 245 miles. That would contradict the data from the chart you referenced unless there are other factors. So I'm wondering if you are comparing data for equal parameters for each car?

[Larry Chanin]

Has Tesla given any word as to how they came up with the range for each battery size?

I have not seen anything from Tesla on how they came up with the range values for the Model S battery packs. However, I find the values released, particularly the 300 mile range, suspiciously nicely rounded. As a result I believe "doing the math" of dividing battery capacity by stated range would probably yield misleading efficiency numbers.

I've heard people say "range at 55mph" but they use the same language "range at 55 mph" to describe the Roadster's range of 245 miles. That would contradict the data from the chart you referenced unless there are other factors. So I'm wondering if you are comparing data for equal parameters for each car?

I believe the chart, and the supporting data, represent a reasonably accurate model that approximates the result of the EPA 2-cycle (city/highway) tests. The EPA puts the 2-cycle results at 245 miles of range. The Tesla model data puts it at about 239 miles of range at 55 mph. That's within 2% of the EPA combined tests.

If I understand the methodology used by radar10 and daxz they started with the Roadster data and applied various multipliers to the factors that effect efficiency, i.e. aerodynamic drag, tire losses, etc. For example, radar10 used a .98 multiplier for aerodynamics, meaning he feels that the net aerodynamic drag considering the coefficient of drag and the cross-sectional area, is only slightly better on the Model S over the Roadster. If I have interpreted daxz's postings correctly, his aerodynamic multiplier would be .88. Since these are ratios applied to the original Roadster data, the issue of comparing different parameters shouldn't arise.

Both of these efficiency values for the Roadster and derived for the Model S do not consider losses in the charging system. Other efficiency numbers quoted for the LEAF in the U.C.S. study do include charging losses.

Larry