# Forums

## Does anyone know the Wh/Mile for Ideal miles?

I've seen the figure 300 Wh/Mile for "Rated" miles but does anyone know what the Wh/Mile would be for "Ideal" miles

DouglasR | 20 June, 2013

It should be around 270 for a 85 kWh car. Rod and Barbara did a computation, but I don't have time to look for it now. Try www.volkerize.com.

Rod and Barbara | 20 June, 2013

@ chicagoniner - My estimate for the Wh/M for an Ideal Mile in the 85 kWh vehicle is between 265 Wh/M and 271 Wh/M. There are a number of ways to calculate this value and all of them contain a fair amount of data scatter. Therefore, it takes a lot of data points to hone in on the correct value. I normally use Rated Miles so I don't have a lot of data on Ideal Miles. One of the keys to the puzzle is determining the Max Range charge Ideal Miles for a nominal battery. To my knowledge, Tesla has not officially published a precise value for this. FYI, my calculation for the Wh/M for Rated Miles in the 85 kWh vehicle is between 306 Wh/M and 308 Wh/M.

chicagoniner | 20 June, 2013

I've been getting 281 Wh/Mi average since I got it and I'm consistently beating the rated miles and wondered how much more cautiously I'd have to drive to achieve "Ideal" miles.

Bob W | 20 June, 2013

85,000 Wh / 300 "max ideal miles" = 283.3 Wh/mile ideal range
85,000 Wh / 265 "max EPA test miles" = 320.75 Wh/mile rated range

But, you don't get to use all those Wh; the car will read 0 miles left after you've used up 81,620 Wh.

81,620 Wh / 300 = 272 Wh/mile ideal
81,620 Wh / 265 = 308 Wh/mile rated

To add even more confusion, the official Dept. of Energy "mileage" sticker for the Tesla Model S displays "38 kW-hrs/100 miles", which is 380 Wh/mile (!). I think this must represents total energy consumed out of the wall socket to charge the car full, including energy lost as heat when charging. So, ignore that for now.

As mentioned, the Energy app. currently plots about 308 Wh/mile as a solid line indicating rated range. But from my calculations, the "rated range" displayed on the other display, in the Instrument panel, uses 300 Wh/mile, which is inconsistent, optimistic, and confusing.

Example anyone can verify: Energy app. may report that you've averaged 340 wH/mile (my usual), and estimates based on state of charge and that you can go another 170 miles "projected range" (be sure to tap the "Average" button, not the useless "Instant" button).

340 wH / mile * 170 miles = 57,800 wH (57.8 kWh) = your current state of charge remaining

57,800 wH / 300 = ~193 miles rated range (and this will be almost exactly the number displayed on the instrument panel, which just seems wrong). It should be 57,800/308 = ~188 miles.

Then again, you know that the Model S will keep going at least until that instrument panel number reaches 0, and maybe 5-15 miles (?) beyond that point, depending on conditions.

Projected range of course will always just be an approximation. Got head winds? Climbing a mountain? Is it raining or snowing? Do you have lots of people in the car, and heavy luggage? Is it really cold or really hot? All of these impact the real range far beyond a simple calculation based on state of charge and some estimated or measured average.

gasnomo | 20 June, 2013

Bob,
Thanks for the info, I had always done the calcs using 85000, where did you find that the car will read 0 miles after using 81.62KWH?

DouglasR | 20 June, 2013

@Bob W - I had never thought of calculating the remaining charge in the battery by using Projected range from the energy app, and then using that to check Rated range on the speedometer. It's pretty interesting that they differ.

I usually use the Trip Meter data ("Since Last Charge"). The problem there is that the Trip Meter does not measure energy use when the car is stationary, so any vampire load is not taken into account, whereas the Rated range on the speedometer does reflect vampire load. I suspect, but have not verified, that the trip meter also does not account for accessory load (vampire load) even when the car is moving.

BTW, a watt-hour is abbreviated Wh, not wH. The "W" is capitalized because it represents someone's name. So kWh, not Kwh. "A" is also capitalized for Ampere.

chicagoniner | 20 June, 2013

Thanks for the info. I've actually achieved ideal miles for good stretches then.

c.bussert67 | 20 June, 2013

I'm with you, chicagoniner. When I take it easy, I get somewhere in the 280's. I can drive to work, have the car sit overnight for 8 hours keeping the battery happy. In the morning I warm the interior up remotely, then dive home and still get 'rated' mileage. Basically, my miles click off at the same rate as rated at the end of the trip, but my extra efficiency has compensated for all the other losses. My average over the last 2000 miles has been 294Wh/mi.

Bob W | 20 June, 2013

@cfriedberg - The 308 Wh/mi number seems to be the general consensus of what the EPA rated range is, based on this TMC thread and this EV range calculator.

Others have discovered that the car has a bit of a mileage reserve below 0 miles displayed, and it will shut down completely well before the battery gets to a zero state of charge (since that would permanently harm or possibly even "brick" the battery).

@DouglasR - correct. I had it right at the top ("Wh/mi"), then messed up at the bottom. :-) Oh how I wish this web site supported "Preview Post", and "Edit" features.

Brian H | 20 June, 2013

Also, Ampere, Volt, and Farad. And even Ohm. All names.

Rod and Barbara | 21 June, 2013

@ Bob W – The data you present using the Energy app to calculate the Wh/M for a rated mile is very interesting. I have used a similar method for some time in an effort to calculate the Wh/M of a rated mile. When the trip meter turns over to 30.0 miles, I note the Wh/M in the trip meter, the projected miles for the last 30 miles based on the average Wh/M, and the rated miles. I never thought to check to be sure the Wh/M at that point in time is the same on the trip meter and the Energy app – certainly it should be. These data points have quite a bit of scatter, with the rated mile efficiency ranging from 301 Wh/M to 317 Wh/M. I just went out to my car and got the current data from the Energy app – 369 Wh/M over the last 30 miles, with a projected miles based on the average Wh/M of 163 miles, and rated miles remaining of 193 miles. This results in a 312 Wh/M for a rated mile (369 x 163 / 193). So I am wondering why you are seeing different results. Do you have a 60 kWh vehicle? The Wh/M for a rated mile is different for the two vehicles – about 307 Wh/M for the 85 kWh vehicle and about 301 Wh/M for the 60 kWh vehicle according to my calculations.

Bob W | 27 June, 2013

Interesting that you see different results. Do you have a P85?

I have a standard 85 (not Performance, so 19" tires). I'm running 4.5 (1.33.48). 21" performance tires have higher rolling resistance, so therefore slightly less projected range?

163 projected miles * 369 Wh/mi = 60147 wH (curr. usable state of charge)
60147 wH / 300 wH/mi = 200 mi rated range
60147 wH / 308 wH/mi = 195 mi rated range

So I am surprised that you see 193 displayed instead of either of these two numbers.

exPGAhacker | 27 June, 2013

I love you guys!

Why anyone would want to drive this car for ideal miles is beyond me!! Drive this baby the way it deserves to be driven. Save all your calculations for when you drive your Leaf or Active E or Focus or whatever else.

This car is a performance car... as in speed. Not performance as in "ideal miles Wh/mi" stuff. Help market the car for what it is. This is starting to sound like a tree hugger's EV site!

Help!!!!!

pablodds | 27 June, 2013

Let her rip guys... I am with exPGAhacker, I drive my P85 like I stole it. Love to see fast cars behind me trying to catch up to see what car it was that just passed them.

Mathew98 | 28 June, 2013

I've been feeling kinda an outcast since my average Wh/mi usage has been in the 600's. Granted I've only driven the car for 200 miles...

Hopefully my usage will come down gradually.

Who knew driving a MS can cure mid life crisis...

DouglasR | 28 June, 2013

@exPGAhacker - I don't drive fast on road trips because that would take me longer to get where I'm going.

Kimscar | 28 June, 2013

Actually the W/mi is a important number to know exPGAhacker.

When you fly a plane you know what speed to glide at to cover the longest distance if you lose your engine. You don't expect to use this but if the situation comes up you have that info.
Most of the time the drivers won't need that information in a Model S. But the situation can come up where you don't want to stop and find an outlet or maybe there isn't one in the area where you are or the headwinds are reducing your range etc...
Tesla should publish the best W/mi number.

NKYTA | 28 June, 2013

@ exPGAhacker

Around town, it's whatever bolting and speeds I feel are safe, and won't get me a ticket.

@ DouglasR

Yep. Cruise control on, keep an eye on miles left, rated, projected - adjust as necessary.

exPGAhacker | 28 June, 2013

I always get a kick out of needing to explain myself because I didn't do a decent job the first time. It usually happens when I think I'm being somewhat whimsical and funny.

I totally get why it's important to maximize the Wh/mi in certain circumstances. But most of us drive the car locally with a long trip or two on occasion. In a single day around town I have yet to even worry about range. The most miles I've driven in a single day of "normal" use is about 170. I rode her hard, too!!

When I do a longer trip, I drive with A/C and around the speed limit, plus or minus 10 (15!) MPH. The important thing is the pre-planning. I don't test the limits. I drive for fun and pleasure and make it work by planning and not testing the limits.

I didn't buy this beast to worry about ideal watt hour per mile calculations and GLIDING to the nth quadrant degree of percentile expectation of the rated range on the EPA rated amperage thingy on the data scatter of a normal rated battery blah blah blah.

Head winds? F**k the head winds! Just drive the car as it's begging to be driven and the only important measurement will be how wide that smile is on your face!

Bob W | 28 June, 2013

Anyone with a P85 (Performance 85) or a 60, please try this:

Open the energy app., and tap Average
Using only numbers displayed by the app., multiply the Avg. Wh/mi (on the left) by the projected range (on the right). This gives you your current state of charge (in Wh), not counting the ~4% reserve. You should get about the same number no matter what distance you select (5, 15, or 30 miles).
Divide the calculated state of charge by the EPA rated range displayed on the instrument panel to get the fixed Wh/mile number used by your car. Please post your car type, and the final number.

For my standard 85, it seems to use 300 Wh/mile. I speculate that for a P85, you'll see about 312 Wh/mile. I have no idea what a 60 (or 40) will display, but I'm very curious to know.

As for the other comments, the beauty of the Model S is that you can drive it for range and comfort, or you can drive it for "sport" (speed).

You can tell a lot about a person's driving habits just by looking at their average Wh/mi in the trip meter. If the auto insurance companies were smart, they would use that number as a factor when calculating your premium. :-)

Bob W | 28 June, 2013

Oh, and please include your software version too, unless it is 4.5 (1.33.48) which is what most of us have at this point I think.

Rod and Barbara | 29 June, 2013

@ Bob W – Thanks for the info on your car configuration. The data difference between our cars is all the more perplexing since we have the same configuration – standard 85, 19” wheels, software v4.5.

On June 27 you wrote:
“60147 wH / 300 wH/mi = 200 mi rated range
60147 wH / 308 wH/mi = 195 mi rated range
So I am surprised that you see 193 displayed instead of either of these two numbers.”

The reason the data don’t result in an exact match is that I find a lot of scatter in the data collected as I described. After collecting 60 data points on many different days and in many different situations I found the calculated Wh/M for a rated mile varied from 301 to 317. To make the situation more confusing, an alternate method for calculating the Wh/M from charging data varied from 299 to 310.

The best way to handle such significant data scatter is to take lots of data points and assume the data errors will form a normal distribution. Then you can calculate the mean, select a confidence level and calculate the confidence interval for the data. For example, my data show that with a 99% confidence level the actual value of the Wh/M for a rated mile is 307.3 plus or minus 1.0 (i.e. between 306.3 and 308.3).

The data that you get from your June 28 request may also show significant scatter. I’ll collect a few data points using your technique over the next week and post the results.

On a side note, since the title of this thread is about Ideal Miles, I wonder if you might get more responses to your request for data if you posted in the Calculation of Rated Range thread.