Model 3

My Wh/mile is high, what's going on?

So this is intended to be more of a basic explanation to beginners to help them understand the Wh/mile metric specifically in regards to winter usage. It hopefully will show them that their usage is either normal, or give a reasonable explanation for their higher usage.

So your Wh/mile rating is high and you either want to know why, or you want to know if it is "normal". There are many reasons this can happen, and many ways to deal with it.

TL:DR(too long, didn't read). If you really want a TL:DR, here is my attempt but you really should read the rest, it's not that bad. Short trip and by extension multiple short trips are worse than long trips. This is because the energy use that goes into the Wh/mile(efficiency) value is better averaged over long trips. That's pretty much it, you'll have to read the rest to get more detail.

First things first. Where does the Wh/mile number come from. This accounts for all the energy used while in a driving mode(everything but PARK). In the winter when you have the heat on, and you are stopped at a light, all that heating energy will be added into your Wh/mile average and will decrease your efficiency(higher Wh/mile value).

So quick list of things that will cause lower efficiency(higher Wh/mile value):

Speed - The faster you go the more aerodynamic drag there is and even more power is required to overcome that drag force. In short, if you are going over 75-80 mph please don't complain about low efficiency.

Wind - This adds to, or subtracts from, your drag due to air resistance as discussed under Speed. For example if you are going 70mph and have a 10mph headwind, your car is going 80mph in terms of air resistance.

Rain/Snow - Rain and Snow increase rolling resistance. In these conditions you will have a measurable decrease in efficiency.

Outside temperature - I am only mentioning this to discount it technically. Outside temperature in and of itself doesn't really do anything. You can make some generalizations about temp vs air density but that is getting into the weeds for this discussion.

HVAC settings - So here is probably the biggest reason for increased power usage and decreased efficiency, especially in the winter time. The A/C during summer will have an effect as well but not near as much as your heat usage in the winter. When you get into a cold car, lets say 30F(cabin, outside temp...) and turn on your heat to whatever you decide, the heating element(or heat pump in newer cars) turns on to the max. Now the Heat pump(newer vehicles 2021) is drawing far less power than the heating element in the older cars(2017/18/19/20) and I don't have any numbers on the heat pump but this will still be a big draw at the beginning. So where you can help out is if you are able to have your car plugged in at home then before you leave for work or wherever, take out the App and turn on your climate. This will preheat the cabin and prevent that energy from being accounted for in your efficiency number.

The amount of energy required to maintain your desired cabin temperature is dependent on your desired temp, the Outside Temperature, as well as the heat loss caused by the outside conditions and how you are driving. Sitting still with no wind will have less effect than going 70mph down the road.

The other thing that can increase your cabin heat usage is not being on Auto and having the fan setting too low for the conditions. If for example you get into the car and turn on the heat but set the fan setting to a 1, then you will draw more power for a longer amount of time. This is because you may not be providing enough heating air flow to overcome the heat loses, and it will just take longer because of low air flow.

NOTE: I have a 2018 LR RWD which does NOT have a heat pump. If you have a Tesla with a heat pump, things work a bit differently and the efficiency hit for using the heat isn't as bad but it is still there and doesn't negate the concepts I am talking about.

So, those are some of the big reasons for decreased efficiency, but how can that relate to your specific driving patterns? Well there are two main driving conditions in my mind. Short trips and Long trips. The definitions of those are pretty wide and don't really matter too much but we can show some things with examples. I hit my character limit so please continue reading the first post below about Short Trips vs Long trips to finish this tutorial up.
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Comments

  • SHORT TRIPS:
    The definitions of those are pretty wide and don't really matter too much but we can show some things with examples. If for example you are spending the day doing multiple stops running errands and you stop for more than a few minutes in 30F temperatures, then your cabin cools down very quickly. This will require the car to heat everything in the cabin back up when you get back into the car and start driving off which will decrease your efficiency. Now there are ways to fix that but it is at the expense of your battery capacity as the power has to come from somewhere if you are not plugged in. You can leave the HVAC on in the settings when you get out and the car will maintain cabin temp. You can also, a few minutes before you get back into the car, get on the app and turn on climate. If you are plugged in and charging then both these options just costs you $, but if not plugged in then it costs your range. So as you can hopefully see, a bunch of short trips will cost you more power and it is a game as to whether you want to save total power and time at the expense of your Wh/mile number, or if you want so save your Wh/mile number at the expense of total power and time usage.

    LONG TRIPS:
    Hopefully you can guess that long trips will be better. This is because you are only maintaining your cabin temperature instead of heating up your cabin multiple times throughout the day. This also allows the energy usage to get averaged over the longer distance traveled.

    Remember also that I am only concentrating on your Wh/mile number and NOT your cars RANGE. This is because a high Wh/mile value will decrease your expected range, but a decreased range does NOT always equal a high Wh/mile value. This again is because the Wh/mile value is only accounting for power used while in a driving mode.

    If this helps even one person understand their car a little better then I have succeeded in my mission. I hope it wasn't too hard to read or follow for anyone but if anyone has questions, please ask.
  • One last comment... There are a lot of people that rename one of the Trip meters to something like "Lifetime, Do not Reset" to keep their running average for their total miles driven.

    I accidentally erased mine after 20k miles, I was not happy.
  • If your Wh per mile is high (and your miles per kWh down) means your driving style and environment are using more energy than the EPA rating to get EPA rated miles.

    Best to get TeslaFI.com as you can track your rides and see exactly where the energy is going on every trip.

    If you go to the Energy/Consumption graph, you can see the line for Rated Wh/mile and see your current and average Wh/mil as you drive. It also provides Projected Range along with the Rated Range line for reference.
  • That was a good post. I'm in the middle of our first long trip on the new 2021 M3 LR. Some figures would have been nice, so I'm throwing some for others to compare. Wh/mile before the trip was about 240, with a lot of short trips, and pre-heating the cabin (and battery, since app doesn't allow to do that independently. Tesla: PLEASE fix that), most of the time car not hooked up. We charge to 80%, unplug, and recharge around 60%.
    The first leg of our long trip was 600+ miles, at 80+ mph most of the time, in 30-60F weather, and we got about 340 Wh/mile. We got a heavy head wind, just like I suspected, so we were charging for a minimum of 30% range, to arrive with at least 20%, for a bit of cushion, in case of a wrong turn or something. Due to those unexpected higher demands, we got to 2 superchargers in the 20s, but never below that, so the figures from ABRP were basically spot on.

    Finally, the car's nav doesn't allow to program it that way, so it stops at the longest supercharger possible, even with 5% remaining (and limiting speed to 70 mph), so I always used what ABRP suggested (for a min of 30%), and the 2 legs that didn't have any unexpected conditions, it was dead on, arriving with exactly 30%. By the way, I used the 240 figure on ABRP, but with the extra 200-lb weight, 32F cold temperature, and 15% over speed limit. And the algorithm probably came out with 340, but will play with it with just 340, and not messing with the rest of the variables, and see if it throws the same figures. Without that program, I'd have had no idea how much to charge to safely arrive at the next supercharger, so I highly suggest it, especially with a new car. Right now on TX highways in cold weather my car gave me 2.5 miles per % of range, so now I have a pretty good idea what I need to charge depending on the range to the next supercharger. I don't like charging more than 90%, and don't like getting with less than 30% (for a good cushion), so that means I have a range of 60%x2.5=150 miles. And the 4 superchargers on the way had from 98 to 147, so that worked out great. Yes, it was slower than with ICE cars, because we stopped very little, but it was fun. Hope this helps too.
  • > @elptxjc_98581461 said: Without that program, I'd have had no idea how much to charge to safely arrive at the next supercharger."

    If you looked at the Projected Range in Energy/Consumption you would know without having to use ABRP. Car will give you the differential between Rated Range and Projected Range.

    StatsApp for Tesla does a nice job of summarizing that on one screen but it's right from the car's info of Projected Range and Rated Range.

    https://imgur.com/ymkHFJZ

    If you watch Energy/Consumption's Projected Range as you drive and charge it will show you actual range so you know to charge 20%(?) more to get to next charger.

    https://imgur.com/pQtrPlL
  • This is a very helpful post for new owners. The only thing I would add is that wind resistance goes up with the square of the speed so there is much more of a range hit going from 70 to 80 MPH than 60 to 70 MPH. In addition, the energy from pebble or other debris strikes goes up with the square of the speed as well. So, you are much more likely to get a cracked windshield from a pebble strike at 85 MPH than 70 MPH. Speed kills range, windshields and paint.
  • @elptxjc_98581461 yea, I didn't want to get into a numbers debate with people cause there are so many variables. I guess I could say that in the winter time, getting 300Wh/mile or over is not out of the ordinary. Over 400Wh/mile and I would say you there is and out of the ordinary reason(probably driver caused)

    @billtphotoman I covered it under "Speed". I didn't want to get in to the nitty gritty math on it because "wind resistance goes up with the square of the speed" doesn't mean anything to a lot of people. This was meant to be as simplistic as possible.

    ABRP is a great program and I have used it mainly for overall planning purposes but it is not required generally to ensure you charge enough to get to your destination. If I am ever worried based on conditions or mountains I'll just make sure the in car navigation says I'll have 30% at the next charger. I would say for >90% of situations this would work just fine. There are obviously some exceptions.
  • One tab over is the appropriate tool. The trip tab tells you soc for where you are going. Consumption tells you for where you have been.
  • You forgot to mention how changes in elevation (even if gradual) affect things. Big difference. It is the one that threw me off for awhile.
  • on my 2019 SR+ with 18" aeros, my wh/mile used to be average 219 with keeping speeds at or below 70mph. I recently changed to 19" turbine aftermarket wheels which weigh 6 lbs more than my 18". Now since the change, my wh/mile is 234 with same driving speeds. Is this a reasonable number expected w the 19" wheels???

    tia,

    Ian B
  • > @ibladuell_98727009 said:
    > on my 2019 SR+ with 18" aeros, my wh/mile used to be average 219 with keeping speeds at or below 70mph. I recently changed to 19" turbine aftermarket wheels which weigh 6 lbs more than my 18". Now since the change, my wh/mile is 234 with same driving speeds. Is this a reasonable number expected w the 19" wheels???
    >
    > tia,
    >
    > Ian B

    Yes
  • > @Bighorn said:
    > > @ibladuell_98727009 said:
    > > on my 2019 SR+ with 18" aeros, my wh/mile used to be average 219 with keeping speeds at or below 70mph. I recently changed to 19" turbine aftermarket wheels which weigh 6 lbs more than my 18". Now since the change, my wh/mile is 234 with same driving speeds. Is this a reasonable number expected w the 19" wheels???
    > >
    > > tia,
    > >
    > > Ian B
    >
    > Yes
    >
    >

    Thanks Bighorn.

    Ian B
  • > You forgot to mention how changes in elevation (even if gradual) affect things. Big difference. It is the one that threw me off for awhile.

    I thought elevation was a known factor in the car’s calculation - from a long ago post, perhaps by Bighorn?
  • @Pappi it should be but it is something to keep in mind just in case.
  • As you correctly say, many variables play. With regard to interior climate control, I have one additional question:
    Assuming that all other variables are equal except this scenario with interior temperature to target, let's say 71F and outside temperature of 45F:
    1. MANUAL instead of Auto and A/C OFF, fan speed at 3
    2. AUTO instead of Manual and A/C ON
    In which of the two scenarios will I consume less wh/mile ?

    Based upon recent short trips, I have a gut feeling in favor of scenario 1. but it would need a much longer trip of at least 100 miles with the many other factors being equal like same outside temperature, same itinerary, same SoC and battery starting temperature, etc. and thus difficult to repeat.
    Has anybody already tried this out or inside knowledge ? Even better, if scenario 1. proves to be more efficient, to what percentage roughly ?
    Thx.
  • Are you trying to heat or cool the cabin?
  • > @T_Scheen said:
    > As you correctly say, many variables play. With regard to interior climate control, I have one additional question:
    > Assuming that all other variables are equal except this scenario with interior temperature to target, let's say 71F and outside temperature of 45F:
    > 1. MANUAL instead of Auto and A/C OFF, fan speed at 3
    > 2. AUTO instead of Manual and A/C ON
    > In which of the two scenarios will I consume less wh/mile ?
    >
    > Based upon recent short trips, I have a gut feeling in favor of scenario 1. but it would need a much longer trip of at least 100 miles with the many other factors being equal like same outside temperature, same itinerary, same SoC and battery starting temperature, etc. and thus difficult to repeat.
    > Has anybody already tried this out or inside knowledge ? Even better, if scenario 1. proves to be more efficient, to what percentage roughly ?
    > Thx.

    ...what's the airspeed velocity of an.... No you are overthinking this one for general use. You will never be able to test between those two cases unless you are on a dyno, and in a temperature and humidity controlled wind tunnel. It's probably a toss up between 1 and 2 but is going to HEAVILY depend on humidity. You are ignoring what A/C is doing and it's importance.

    Not think about this... drop that outside temperature to say 0F, now what happens? Well being on Manual and fan speed of 3 might not give enough warm air volume to overcome your cabin heat losses, which would in turn cause the heater to try and push more heat through that small(fan setting 3) "pipe", you may not ever with in that scenario.

    You can try and game the system by messing with all your HVAC controls but in the end the difference is probably negligable and AUTO is a just fine option. Auto turns into a negative when the car decides to pump a massive amount of heat towards your feet which gets very uncomfortable over time.
  • Ok, thx derotam.
    One last question, when you say:
    "You are ignoring what A/C is doing and it's importance"
    Could you eventually elaborate on that one ? In other words, A/C to OFF in winter timer is not such a good idea ?
  • > @T_Scheen said:
    > Ok, thx derotam.
    > One last question, when you say:
    > "You are ignoring what A/C is doing and it's importance"
    > Could you eventually elaborate on that one ? In other words, A/C to OFF in winter timer is not such a good idea ?

    Its all about humidity. If you get too much humidity in the cabin in the winter time your windows will fog up. The other thing you didn't mention is re-circulation. A lot of people want to turn re-circulation on so that they aren't expending more energy to heat up the cold outside air but unfortunately this tends to allow the humidity level in the cabin to go up faster and then the A/C is running more to deal with the increase in humidity so they are probably using more energy.

    In the end, for general operation I think it is best to say just leave everything on AUTO. There are a lots of different situations where someone might want to change something for a specific reason but I think AUTO is a good general guide.
  • Still winter time folks!
  • Snow storm coming for me!
  • @ceeg please read the OP for this thread.
  • ...another happy customer 😀
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