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Energy-efficient driving

I am currently experimenting with ways how to drive my Tesla as energy-efficiently as possible, and I have found a way where preliminary results show a 10% reduction in consumption.

Story: I currently have a loaner, provided by the fantastic Denmark Tesla team, when my 12-V Battery malfunctioned for the 3rd time in 3 weeks - they actually transported a loaner 400 miles to Stockholm and brought down my car for repair - WOW!!

This loaner, though, consumes about 10% more energy than my proper car with identical trips, identical settings and, as far as I can see, identical driving. Because of an imminent long haul this concerned me very much, so I started to think of ways of bringing down the consumption. I got the advice from a Tesla man: drive it as you would drive an ICE.

OK, fine. I have developed a style of driving with ICE:s that invariably beats their own consumption figures (and we all know that they are the "optimal" ones anyway). It is quite easy - roll the car in Neutral as much as circumstances allow.

I tried this with the loaner, and it immediately yielded really good results - minus 10%, from 310 Wh/mile to 278 Wh/mile in 40 degrees F.

The Tesla is built with such a small wind and rolling resistance so that these 2 factors coupled with the huge mass makes the Tesla roll "for ever", especially in a down-slope. If there's just a small decline it doesn't even lose speed.

The gearbox is so well-made that I learned in less than 2 minutes how to change back and forth between Drive and Neutral without anyone noticing anything.

So, if you free-roll and want to lose speed, put it in Drive and engage re-gen. If you want to keep the speed or increase it, just put it in Drive and - well, drive.

The Cruise Control doesn't do this well - it constantly gives small "puffs" of energy and then brakes, for instance when you reach a small hill, and the re-gen cannot be 100% efficient, so you lose more than you gain, whereas, if the hill is small enough, you just roll over it in Neutral or you see it coming and accellerate slightly BEFORE the hill and roll down after it (never accellerate uphill, if it can be avoided).

This car has such eminent rolling features that this can be done without at all disrupting the traffic flow, if applied intelligently (mostly meaning rolling downhill, but also anticipating a traffic jam or light).

I called Tesla and asked them if this could in any way, shape or form damage the car (I am driving a loaner, and I am much more careful with other people's properties than with my own), and the answer from the Danish SC was an unequivocal NO.

My lifetime average consumption (incl. the multiple showing-off accellerations in the beginning - I am only human...) with my proper car is 289 Wh/mile, with the temp has varied between 29 F and 50 F. Applying the free-roll system, I think I will get it down to 260 or thereabouts. Will keep you posted.

Would be interesting to hear, if anyone else has tried this and their experiences.

Robert

At low speeds drag is not the real issue, so if we are talking about the speed increasing from 20 to 30 MPH - not an issue. I first contemplated this issue after talking to other MS owners at the Folsom SC where someone mentioned that he had hit 110 MPH coasting down from Tahoe. Drag is clearly an issue at this speed. In fact I think that if you look at the MS' range vs. speed data you will see that drag is the dominate factor in determining range at speeds, say above 50 or 60 MPH, as the range goes down with the square of the speed.

Interesting academic discussion but seriously guys. I am all for saving energy. That's why I got the Tesla and trying to get solar for my roof. Frankly I usually have more than enough charge on my battery for my daily needs and on the occasion that I am running tight I am not sure how many real world miles you are gonna save. Rather than traumatize myself worrying about when to switch from neutral to park I would rather stop off at a Blink station and grab a cup of coffee to get me back those 10 extra miles.

Sccrendo,

Actually I agree with you. My wife and I used to carpool in our 2006 Honda Insight and I used every trick in the book to keep our trip mileage above 70 MPG. Believe me there is no one more smug or self-righteous than two vegetarian Sunday School teachers carpooling in a car that gets more than 70 MPG. Unless of course, you are driving a Tesla powered (largely) be solar panels. Problem the Tesla is just too much fun to drive to poke along at 45 in the right hand lane or take it easy coming out of a corner. You won’t catch me doing that unless I am very low on range. Go for it.

@robert@bis.se - thanks for sharing this. i tried this first thing in the morning for my local non-highway driving and I can see a big difference. i will keep trying this as and when it can be safely done without distracting my driving.

Re. the parking brake - remember that at speed (not sure what the cut off is) the 'P' control switches from a parking brake (toggle on) to an Emergency Brake (push/hold on, release off)

Just drive 25mph. You'll see a dramatic increase both in range and "saving the planet" - well beyond shifting to neutral.

Wow, I just drive my car and drive it like a moron. I don't ever think it has been over 75mph but it has so many 0-60 runs that it's not even funny. After 6 weeks we're still under 1000 miles because we don't drive on freeways or long distances.

Our average energy is 375 Wh/mile! I guess if we really want to sell it four years from now I'll have to work on driving it at 30mph for about a year to average it down.

On the plus side it's stored in a garage at all times, is plugged in every minute that it is not driving, lives in the nice climate of Southern California and will never see snow or salt.

I seriously don't put any thought into how I drive it. I just have a lot of fun with it.

@Thomas N

How dare you simply enjoy your car. This forum clearly dictates that one must (kind of afraid of using the word "obsess") sweat the details in order to get the true Tesla experience.

Keep it up and someone's going to put a crease in your frunk. :-)

+1 jtodtman

I'm totally with Tom however have over 14000 miles in 6 months. Average wH/mile = 346 since I got the car and I do mostly freeway driving in the HOV Lane. Not sure I am gonna put it into R, N or P anytime soon.

Just a word of warning. Power is control is what you learn driving ships. Never ever risk not to have no power available. In "normal" driving situations that might not be any issue. But you should not plan for those only. If, to avoid an accident, trying to get the gear back in is the difference between a little throttle to make a turn wider to get past an obstacle or whatever and hitting something, you might (if you still can) regret this.

People tend to be overconfident of what they can do in normal situations, not applicable to the rare but not to be excluded non-normal events. I would rather try to keep the car with a sensitive foot in coasting or ask TM to make the bandwidth wider in which the car will by itself not accelerate or regen, as an option (low/high coast range) than to risk not having power available if needed. That's on of the reasons why it is forbidden to have cars in neutral on public roads, not if the transmission can take it or if the power steering or braking works (in most cases today it does in neutral bbut not all!).

I would not want that by the way with the higher coast bandwidth, I want immediate engine response in both ways. Control is life...

RZ;
+1
Yes, that's what I meant and robert didn't get.

Instead of shifting to Neutral, can't you get almost the same improvement by changing the regen to low? I believe this is what BMW has on the i3, they automagically change the regen to low/off? when the vehicle is moving at highway speeds...

I've just hit 303 Wh/m lifetime average and yesterday I averaged 280 Wh/m going to the store. On Wednesday I averaged 250 Wh/m driving home from Scottsdale - about 40 miles. I typically drive about 5 MPH over the limit and rarely exceed 70 MPH on the freeway unless I'm passing. I've had to change my display to Ideal Range because that more closely matches the actual range I get during daily driving.

I set my display to Ideal Range as well and then mentally divide it in half because that's what I'm going to get. They should have a new setting: "Jacka\$\$ Range" and I would be happy.

As hillcountryfull pointed out, one can decrease regen and coast more easily with the Low Regen setting, but the labels clearly imply this will decrease the range.

Tried low regen today. Soft and pleasant, but had to use the brakes frequently. Also tried coasting, but did not save measurably.

Notre: Could you tell a difference in the Wh/mile between coasting and low regen? Thanks -

No, I can't say, but braking wastes energy, so I guess low regen is less efficient. I enjoyed the smoothness though.

Let off the accelerator gently until you zero the power consumption meter. I assume that this is almost the same thing as coasting.

Being able to judge the distance remaining until a stop and how much regen to use is an essential skill. Developing a sensitive right foot also makes for smoother driving. Just enough of a challenge to keep driving interesting.

The zen of one foot driving. . . . . . .

If one is coasting over a block or more in preparation for stopping, the average speed is likely less than going at "full" speed for a bit longer and then using regen to stop. Slower will always use less energy. Using the brakes will always waste energy.

First post here, and haven't received my car yet, but I thought I could add a few points.

Cruise control is absolutely the most efficient way of driving if you are on a flat surface.

However, the cruise control is a "dumb" system - it simply checks what your desired speed is, and either adds throttle if you're under it, or removes throttle if you're over it. It doesn't know anything about upcoming hills, traffics, or turns.

The only way you can gain efficiency over the cruise control via coasting is when you, the driver, can predict when you will be served by purposely losing speed.

So, suppose I'm going 70 mph on a flat road, and approaching a hill.

By "manually" driving the car, I might purposefully allow myself to slow to 60 mph on the way up the hill instead of exerting the energy to both keep the car at 70 mph and increase my elevation. On the way down the hill again, I might let the car coast back up to speed, possibly exceeding my original speed, knowing that it is "free" energy gained from the elevation change.

If you simply leave cruise control set at 70mph, it will "stubbornly" try to keep the car going 70 mph up the hill, which wastes a lot of energy. Then, on the way down the hill, as the car's speed increases over 70mph, the car might automatically apply regen, again to keep you at 70mph.

I have to agree with others that fiddling with the gear selector while going at highway speeds is not really a safe solution, especially since the P button turns into an E-brake. If you successfully use this method to coast smoothly on 99 trips, the one time you do accidentally use the E-brake, assuming you don't get into an accident or break anything, you are still going to waste all of the energy you saved on the other 99 trips by burning it up in the tires and brakes.

I propose a better solution, which is to just use cruise control, and lower your target speed as you approach a hill. This applies to ICEs as well. You will get better efficiency, have an easier time focusing on the road, and still be "ready to react" in the event that you do need a quick response (since cruise keeps it in gear and disengages with the brake pedal applied).

Also, a note about efficiency - wind resistance is an incredibly powerful force. Drag increases by the square of the velocity, but power required to overcome drag increases by a cube of the velocity, because not only is the work being done squared, but it is being done over a higher speed.

A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power.

Furthermore, some types of batteries actually have lower capacity when current is drawn at a higher rate (Peukert's law). Not sure if this applies to Model S batteries, but either way, going fast takes considerably more energy!

@tim. Very nice first post. I am no engineer so I'll be watching to see if and how those who are take your figures apart.

Either way, welcome and thanks for participating.

Twice as much energy, for half as long cancels. Except for the fun. Fun || accel.

Brian H, driving twice as fast gets you there in half the time, but uses more than twice the power. So I don't know what you're trying to say.

J/k.

@RZippel

Tut Leid, aber ich bin wirklich nicht Ihrer Meinung.

I don't agree. Any system used is dependent upon how and where it is being used. If used unintelligently, any system will fail and possibly be dangerous.
First of all, the gearbox is so incredibly fast and smoothe that, if a situation occurs, the time it takes to engage or disengage the Drive is shorter than the delay in answering the pedal in any normal ICE car.

Secondly, in a difficult situation, I would opine that in 99,xxx percent of the cases it is a matter of bringing the speed down, not up. For that the regular brakes are fantastic and certainly good enough, re-generation or not. I don't even think that applying the regeneration shortens the ABS braking distance at all.

Thirdly, when free-rolling, I put my foot at the brake pedal, of course without depressing it at all. That fact alone gives me a MUCH faster reaction time for braking than anything else. Only when I break the free-roll to increase/hold speed, do I move the foot. For reducing speed, I just engage drive; since the foot isn't on the gas pedal, the re-generation starts immediately and smoothly - if necessary (almost never) I press brake.

Fourthly I have during 52 years of driving all over the world (and certainly at least 40 times Stockholm-Basel or more South and return) never encountered a situation, where ADDITION of speed would have helped me in the least, but, even so, I would never overtake anyone or be in the left lane at all without having the Drive in. That would be basically very unintelligent and ultimately dangerous, especially, as often in Germany, someone approaches from behing, left blinker on, in 150 mph (250 kmh)(I know, to my eternal shame I was once one of them, in my MB 450 SEL). Therefore, we can happily change the 99,xxx% to 100%.

Therefore, the whole set of assumptions on your part is wrong, and therefore also the conclusions.

Viele Grüße gen Süden - Robert

@BrianH

"Yes, that's what I meant and robert didn't get."

Normally I do try to keep my posts in a nice tone and in a way that I hope is conducive to the participants in any of the Fora I visit and participate.
However, I have developed a slight antipathy for some of your posts.

I will stipulate that I no longer am quite as sharp as I was when I founded the Finnish Mensa half a century ago, but, dear BrianH, I will also emphatically state that, barring computers and smart-phones that don't hold much interest for me, I D O G E T I T.
If there is anything I don't get, it is most often, because the reasoning that I am supposed to "get" is fawlty (yes, I am an unashamed John Cleese fan), precisely like the post by Herr Zippel, which you +1:ed (see my post above).

====================

While having it out with you, may I also inform you that a fair proportion of this Forum consists of people that do not have English as their first language - maybe not even second (I know for a fact that English was my 4th) and that I therefore think that your constant floccinaucinihilipilificatious (look it up, lock it up) corrections of others' mistakes are misplaced. Yes, the insulted body doesn't propel in the grave, it turns or even rotates, but it was a fair enough translation from Norwegian, and I don't think that any member of this Forum misunderstood the meaning. If you insist of being a Language Police, why don't you spend some time in correcting your linguistic countrymen in the correct usage of it's (abbreviation) vs its (genitive), something that invariably gets mixed up.

- Daddy, why is Internet so good?
- Well, son, it's its IT:s.

Or start writing posts in any of the 10+ languages I feel comfortable in, and experience the sticky end of the wicket.

Having got that off my chest, let's co-operate to make this into a welcoming and conducive Forum, also for those (incl. many of your countrymen, whencever you come) that do not have a perfect command of the Queen's English, shall we?

Best - Robert

Unscientifically, after two short legs, using free-rolling:

Home - ferry to Finland. 32,6 km [20,4 miles] 20 freeway, 6 congested freeway, 6 bumper-to-bumper city). No beam, no A/C. Temp 11 [52]

5,6 kW 182 Wm/km [291 Wh/m].
Take away the first 4,3 km [2,7] for the heating up of Battery.

Rest of Trip: 28,3 [17,7] for 4,4 kW or 155 Wh/k [246 Wh/m]

Energy App, Average: Last 25 km [15] 155 Wh/k [246]
Last 10 km [6]: 138 Wh/k [221 Wh/m]

=================

Ferryboat - home this morning

Including the first 5 km, the relevant data: 160 Wh/k [256 Wh/m]
Excluding the first 5 km: 149 Wh/k [238 Wh/m].

Energy App readins Average: Last 10: 135 Wh/k [216 Wh/m]
Last 25 147 [235]

Speed limits: freeway between 70 and 90 [45 - 56 mph], city 50 [31] (but impossible to hold in that traffic).

Nowhere did I hold up traffic or act as a disturbance. I followed the rhythm, even when it exceeded the given legal limits.

===============

Before anyone tells me that the sample is too small, I agree.

On Thursday I will make the 240-mile trip. I will have a passenger on half the journey and the car will be really packed.

I will produce an exhaustive chart of what happened.

I still believe that the free-rolling system is a safe and very saving feature, if applied with a bit of thought, but let's see after Thursday.

Robert

@Robert

I am a fan of yours since your very first post. I grow more impressed with your knowledge, experience and demeanor with every new problem (did you get to 84 yet?) and I do believe your character comes through even more when you're pissed off at someone. (By the way it was Amped Realtor who called you OCD, Tam was merely defining it.)

Having said that I am also a big fan of Brian H. He is of the opinion that ESL or ETL or EFL posters appreciate being corrected when they use English incorrectly. I'm not so sure that is true but Brian has said many times that education is his intent.

I am quite sure he has expounded on the usage of its and it's in at least three threads. He has a nice mnemonic for it but I can't remember it right now.

He is quite informed about practically everything, Tesla related or otherwise.

Also, he is damn funny at times, but humor is a high-wire act.

I am rooting for you to get your car back from Copenhagen in top notch condition so you can enjoy it without the constant aggravation you've already endured.