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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

@Tesla-David

Yes, this is almost certainly because you use a lot of energy to heat up the Battery to a proper level. I always find that the first 2-3 miles - however much I try - have a huge consumption that only my owning a smart-phone could prevent...

As I said, my 240-mile roundtrip (that is, if I get that far) on Thursday will give me all the answers I need.

Best - Robert

I am an addicted coaster and have saved literally tons of gas over the years, but am not so enthusiastic about continuing the practice with the MS.

10% saving is an overestimation in my view compared to regular driving with a gentle right foot and standard regen.

Percentage saved is obviously much less compared to a similar ICE vehicle and the absolute amount of energy saved is at best slight.

Sorry a little off topic here.

@Brian H, I've always enjoyed your postings. Meanwhile, there's story I will not forget - my high-school best friend wrote me her first letter in English professing our friendship. I took out a red pen, made corrections, and sent it back. She wasn't the same friend that I had ever since. And my intention was totally good thinking she would benefit from my feedback. I suppose human beings have feelings, and I missed it in the name of progress.

I think going down a slope at 80 or 90 kmh with cruise control is more efficient than letting the car roll and gain speed to above 100.

More energy is wasted by increased drag than in regen which I have discovered is surprisingly efficient.

Cindy -

I don't know how that could have been taken any other way! If I were to write somebody a letter in Spanish and profess my feelings about our friendship and they sent it back with red markings all over it with corrections I would never write back again.

@Thomas N. - I'm sure Cindy is his wife's name. Then again, I've been told that I'm wrong quite often. Just ask my boss...

P85+

I regularly travel at 325 Wh/mi but I only drive a maximum of 100 miles per day. Every other weekend I will drive out to a sporting event ~125-165 miles. If it is in the 125-130 mile range I find I'm bumping up against the limit of the round trip (250-260) range without any recharging. Accordingly, I try to drive in a very efficient manner, usually using cruise control the vast majority of the way. I've always considered the current cruise control inefficient, as it will regen to keep the speed constant, and then immediately power up the next hill to keep the speed constant.

I tried using the neutral setting when going downhill, and then into drive up hill at the point my speed started to just go down. My initial impression is that this technique is VERY efficient compared to just cruise control. I would regularly have a hard time keeping <300 Wh/mi, but with just one day of using neutral on downhills, I am easily below 285 Wh/mi, which bodes well for range.

FEATURE REQUEST: A button on the steering wheel (not a new one, just a repurposed one), that allows you to toggle regen fully off or on. I find using the yolk drive/neutral select to be kind of a hack, but it works. And on the touch screen you can only select standard or low regen.

280-285 Wh/mi in the rolling hills of Western NC is great! Intermittent neutral coasting seems to be useful. This certainly will increase my range. That being said, by the end of the year, I should have 4-5 superchargers in range, so we'll see how that effects my efficiency...

Bumping this for AmpedRealtor

Thanks Robert, I'm late to this party...

I have been experimenting more with coasting as well, and have been able to lower my energy usage to about 250 Wh/mi. I have a P85 w/ 19" wheels. I have now switched my display to show ideal range, as I have been getting at least ideal range - usually better - when incorporating a lot of coasting into my driving.

I've had my S85 for more than a year now, and since I am an engineer interested in efficiency I have tried lots of tricks to improve the Model S efficiency. Clearly, coasting to stop or to adjust down your speed is more efficient than using regen, by that factor of 10-20% that is the "round trip" power loss when using regen.

Since selecting Neutral doesn't really disconnect the gears (there is no transmission); all it does is turn off regen. You accomplish the same thing by "feathering" the accelerator to make the power meter zero.

I think there is a relatively easy software improvement that would address 90% of the need to use Neutral to coast.

Right now, feathering the accelerator is rather difficult. It requires quite a bit of concentration to keep the pedal position at the point where the energy in/out is zero. This is because the sensitivity of the pedal is the same (or, at least "feels" the same) no matter whether you are near zero or heavily accelerating/decelerating. What we need is to flatten the response curve near zero power in/out. That would provide a large "plateau" that would be easier to find with your foot, and on that plateau the responsiveness of the pedal would be decreased. The plateau would be located on the power consumption curve, not speed, and so would adjust for going up and down hills, wind, etc.. And making this position easier to find would reduce the cognitive load of driving efficiently, making it more pleasant and more safe.

Would that plateau dampen the response when you try to accelerate. Sure, a little. So accel or decel would be a bit "mushy" near zero. But who cares about small changes near zero? And you could potentially overcome that effect by using the rate of change of your foot position. The mouse on my PC or Mac does this: it's called, coincidentally, "acceleration", and gives your hand a way to "throw" the cursor while still keeping fine control while moving slowly (i.e., by flattening/steepening the response curve as a function of rate of change of position). Similarly, if you "stomp on the pedal", the rate of change would be high, and the software would respond more quickly.

In summary, I'd like to see Tesla provide a driving setting that would allow for a broader "zero power" range for the "speed request pedal".

Good ideers.

It's the "goose pedal", btw.
;p

I like to coast in neutral too, however you need to press brake before you can shift back to drive right? Is there any way around that? It is somewhat inefficient to need to do that if i want to speed up.

@wufucius

No, you don't, absolutely not. That would make coasting impossible. Just use the middle finger of your right hand to go back and forth between drive and neutral, matching the speed with your foot when going to drive. Only if you stop the car do you have to press the brake.

That sounds exactly like how I drive, except I don't have to use my middle finger :-) Just the accelerator.

Bumped

Robert, thanks for the bump. I'd missed this thread earlier. Not just an interesting collection of exchanges but entertaining as well.

One question I had about halfway through this thread… how are you able to compare driving styles and eliminate all other factors? I’ve tried this but the efficiency differences with varying temperatures and wind conditions seems to be much greater than my change in driving style. We’ve had anything from -12°C down to -28°C. Even the starting temperature of the battery seems to have an impact. At anything less than -10°C and I seem to regain some of the dercrease in potential from lower temperatures as the battery warms, this makes the first leg of my commute apparently more efficient than the latter. I’ve read that the battery has as little as 70% of its rated potential below -15°C.

@Tanchico

The answer: I cannot, at least not scientifically. However, since my commute is basically the same (home-school-work and vice versa) and is about 35 miles and undertaken at the same time every day, and since the car starts at the same temperature every morning (heated garage) I can spot tendencies after a while, and that I do.

The car's menu should be expanded to allow something like going into coasting, if you let off the pedal quickly, while using regen if you let of slowly.

Or a button for coasting. Smartly using coasting will increase efficiency.

Pedal should have coasting region between accelerate and regen wide enough to easily keep foot in. Width of it could be user adjustable.

Agreed and also mentioned as a possible enhancement in v6.0: alter cruise control such that highway speeds eliminates regen in favor of coasting.

Maybe Tesla can upgrade to "smart pulse mode" which will allow you to maintain a range of speed (say 5-7 mph) and do so efficiently, by using GPS and maps to anticipate elevation changes.

bump