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Actual Range vs Predicted Considering Wh/mi

Actual Range vs Predicted Considering Wh/mi

I've heard it said the Tesla battery range prediction is based on the standard Wh/mi constant of 241.9. I think the 241.9 is the number used in the EPA battery miles calculation. If that is correct, when I take a trip with a lower Wh/mi average than 241.9, my actual trip miles should be more than the predicted battery miles. The miles I get between charges is never more than the predicted miles. I average 82% of prediction. The 82% average is the number of actual miles between charges divided by the difference between the initial predicted battery miles and the final predicted battery miles. Of course, there are the phantom losses, but things still don't add up. I have a spreadsheet recording every detail of the trip between charges: miles driven, starting predicted miles, ending predicted miles, kWh consumed (by the trip report) and date/time stamp. I calculate what the phantom losses would have to be for the battery prediction to be 100% of actual between each charge based on the actual trip Wh/mile. That phantom charge calculation averages about 12 miles/day. When the car sat at LAX for a week, the calculated phantom charge was only 2.3 miles/day, which is what I think is the real number. I've also heard the Energy graph is better, but I haven't checked it.

My question is how are the predicted battery miles calculated? It can't be based on a Wh/mile constant. If it were, when I have a trip with a low (200 Wh/mile) energy use, I would get more actual miles than predicted miles. Given the way we drive and our climate, my all time Wh/mile is down to 237 over the 12,000 miles and one year of ownership. My last 10 trips between fill-ups of electrons has averaged 225 Wh/miles, yet my actual range is only 82% of battery prediction.

M3BlueGeorgia | 4 aprile 2019

Wrong way around. When Tesla run the EPA test on the LR+RWD Model 3, the usage works out to 241 - 242. Different cars have different results.

Your usage will almost certainly be different, and probably a little worse.

Bighorn | 4 aprile 2019

There is a Wh/m rate constant that varies between different models. 241.9 is not one of them. Assuming phantom loss is the only unattributed consumer is false. Hundreds of pages have been written about this and I often encourage people to not reinvent the wheel because a lot of subtleties derail 99% of the results regardless of the person’s background.

Carl Thompson | 4 aprile 2019

I've noticed that my Model 3's efficiency numbers don't add up too. This is compounded by the readings from my EVSE which has a display telling how much electricity went into the car. My own calculations and those of the EVSE suggest that the Model 3's displayed numbers understate its energy use. How much? I'm waiting for late spring when we have consistent warm temperatures to test thoroughly but so far it looks pretty significant.

gballant4570 | 4 aprile 2019

Mine add up. The break point is somewhere between 235 and 240 wh/m. I consistently get more miles than estimated out of a charge when my wh/m for that charge are in the lower 230's or less. I have some days where my average for the dat is in the 180's, and that is when it become fairly noticeable. If my daily average is 232, I'll only get 5 or so miles more when I add the miles traveled to the remaining miles estimated and then compare to the estimate before I drove the car that day. If I looked too closely, I would find that they wouldn't add up exactly. I'm sure there is some rounding going on, perhaps in more than one place....

cconklin1 | 4 aprile 2019

I find the emphasis on the Wh/Mile numbers provided in the car itself somewhat puzzling...it might reflect driving style and efficiency on a; macro scale...but isn't the real measure the Wh/Mile on a "wall to wheels" basis, that reflects the entire energy use per mile of the car. Over 5,000 miles on my LR RWD 3, I'm showing about 370 Wh/Mile in that measure. And I can tell you that there is absolutely no way I will get 310 miles of range out of the car, regardless of what the display tells me....

Jiver | 4 aprile 2019

Why all of the worry about estimated range? I find that by looking at percent charge I know much more about my battery state and burn rate than using the estimated miles view. The energy screen provides very detailed information on current usage and arrival estimates. Between percentage and the energy screen I have an excellent idea of if I am going to reach my destination or not. Estimated range seems irrelevant.

If I want to know the guess at "miles" I can use 10% = 31 miles (LR AWD). That's what the display would tell me. It would be wrong, though. The energy screen would be more accurate as to how much range I have left. And yes, I could do that in reverse -- divide miles left by 31 to arrive at percent -- but why go to that trouble?

The estimated miles do not take in to account terrain or wind or weather. Percent remaining always does. My drive to work is downhill. My drive home is uphill. I use a greater percentage going home than I do going to work. The percentage display makes sense to me. Estimated miles remaining makes no sense at all. They tick down slower in one direction than they do in the other, and in neither direction is 1 estimated mile = 1 real mile.

gballant4570 | 4 aprile 2019

Before I got my Model 3 I was convinced I would want to see SOC on the screen displayed by percentage. Instead, I find the miles display to be more useful. Along with the wh/m, I know generally what the energy screen would tell me if i displayed in - unless I want to know the instant energy effects of acceleration, etc.....
In my area there are many hills, do nearly every drive evens out rapidly with regard to elevation. There is one part that doesn't - I live near the top of one of the higher hills for miles around, so my wh/m quickly drops from the initial 1200 or so to about 70 on the first 2 miles, all down hill. But I got to go back up the hill when I get home.
I always remeber the estimated miles showing when I leave, and like to add the traveled miles to the remaining estimate and see that the two numbers add up to more than the original estimate. As the weather warms, that happens more and more often.

beaver | 4 aprile 2019

TeslaFi says my M3 LR RWD efficiency target is 217 Wh/mile on 8.3

gballant4570 | 4 aprile 2019

beaver, that sounds a little low. My AWD LR has only ever shown a max of 308 estimated miles on a full charge, but I can increase that to 320 by averaging 230 wh/m. Using 73.6 kwh as available battery size, a 217 wh/m avg should yield a bit over 339. I thought the RWD LR was rated at 325, which at a capacity of 73.6 would require a wh/m avg of 226.46. Now 339 is really close to 325 x 1.05, but my 5% increase does not appear to apply to range.....

gmr6415 | 4 aprile 2019

You can get better than expected range. I go from Central FL to Mayo Clinic in Jacksonville frequently. It's a little over a 360 mile round trip, mostly highway, but there is some stop and go for about a half hour through a few small towns. Before 2019.5.15 I was doing the whole trip with a Wh/mi of between 202 and 220. I do charge when leaving Jacksonville because on my route there aren't any other chargers until I get home. I've attached an image of a trip card where I did the whole trip using 208 Wh/mi. Since 2019.5.15 my car seems to be doing even better (LR RWD).

https://ibb.co/fJcZXU

eandmjep | 4 aprile 2019

On a trip I use the 242 as the target. If I average 218 which is 90% of 242 my range drops 90% of the miles I traveled. It's pretty consistent. Winter changed that but those numbers are back with warmer temps. Lots of driving over days in short bursts charging In between, factoring In vampire drain etc and it won't compute but on a single charge driving for hours the math for me is pretty consistent around that 242.

FremontDave | 4 aprile 2019

I have a SR+, which is supposed to have a range of 240 mi with a 55KWh battery. So this works out to 229Wh/mi. On the Energy Consumption graph, there is a solid "Rated" line of just about that.

My Wh/mi is generally above that (based on the provided trip info). So I usually derate the "miles left" accordingly.

OutOfTheStars | 4 aprile 2019

It has been only 4 days since I got my M3 AWD. My work trip is 30 miles one-way and I am getting around 250 wh/mile range 50% highway and 50% local. I noticed engaging auto pilot improves the range and also AC has big influence. This morning it was a bit chilly in Central Florida and I turned off AC. I was able to manage under 200 wh/mile.

gmr6415 | 4 aprile 2019

@FremontDave, @kanike, Your cars are too new. Give them 2000 to 2500 miles. That's about when I noticed improvement in mine.

Bighorn | 4 aprile 2019

@Fremont Dave
Good for approximations, but 55 kWh is likely not the actual number and the "Rated" line has never quite matched the true ratio.

coleAK | 4 aprile 2019

So the range number on the battery meter never changes, it’s set to a default. That is why I keep it set to % instead of miles. I’ve found the energy app in the car set to the longest 30 mile window is a pretty good predictor of range. It’s much like the trip mpg in ourICE cars.

FremontDave | 4 aprile 2019

@Bighorn How should I derate the "miles left" then given a specific Wh/mil (e.g. mine is usually 270)?

coleAK | 4 aprile 2019

@dave. Is it always 270 miles left in the energy app graph? Or on the useless battery meter? The battery meter never changes it’s based on the EPA rating ~240 Wh/mi.

Bighorn | 4 aprile 2019

What I’ve done when on long, uninterrupted trips, I derive the battery capacity by extrapolating from kWh used over a delta SOC. I also look at delta Rated miles vs kWh used. You can also derive capacity in kWh by multiplying your derived Wh/RM by rated miles at 100% SOC.
My P3D has a rate constant of 234 Wh/RM. The LR RWD is closer to 219. I suspect the SR+ is better still.
Unlike the Model S, kWh data is not granular to the tenths place, so precision is not as good without access to better data from programs such as TeslaFi.

WardT | 19 settembre 2019

FWIW, I’ve done some more testing on short and long trips to understand why my predicted battery miles is off. I have found on short trips, say 20 miles, the calculated battery miles before and after is based on a constant 219 Wh/mi. On a longer trip, say 200 miles, the calculated battery miles before and after is based on a constant 222 Wh/mi. I suspect these two estimates are really just the variance in my testing and the battery miles is based on the same Wh/mi in both cases. When taking a trip, I get more battery miles than predicted if I drove slow and used less than 220 Wh/mi. If I drive such my Wh/mi is higher than 220 Wh/mi, my battery miles is less than actual. I’m averaging about 234 Wh/mi and usually get about 85% of the battery miles. Seems like Tesla would adjust the Wh/mi like the energy screen shows.

Bighorn | 19 settembre 2019

@ward
218 give or take is the rate constant for the RW drive and 234 is for AWD.

Bighorn | 19 settembre 2019

Also
You shouldn’t be seeing that big an efficiency hit consuming 234 Wh/m. About half that. Maybe you’re not doing a continuous run?