[davidwhodge]

I make an app (called Nikola, not the truck company) for Tesla owners that has seen over 5 MM miles driven on it. I did some quick queries to validate actual range vs. EPA range for those curious.

My general takeaway is to see the EPA range as a useful, albeit unrealistic, indicator. Essentially nobody gets the EPA range, either because they choose not to go the speed limit, they accelerate harder than the EPA test factored in, or the vehicles drain some juice while parked.

The data: For the hundreds of Nikola trips with an average speed of 60 mph, the actual MPGe was about 102. Once you get up to a 75 MPH average trip speed, the MPGe drops to 94. And by 80 MPH the MPGe drops to 77. (avg over all Tesla types)

As a bit of "anecdata", I've driven trips where I hit my range on the nose, just to show I could, but the driving is less fun and I was going slower than traffic. I don't drive that way anymore.

What's most striking to me as someone who has heard over and over again about how air resistance is a X^2 property, is the extent to which short (and presumably slow) trips punch above their weight in terms of range consumed per mile. From what I can tell, the actual cost here is the fixed cost of booting up some systems and electronics, and the variable costs of running them over fewer miles can make the MPGe drop. Starting and continuing to run the AC adds up!

edit: have had some people ask. The app can be found at https://download.nikolaapp.com

I can also post data / graphs or make a blog post about that if people have more requests. Let me know what you'd like to see!

[chongli]

For the hundreds of Nikola trips with an average speed of 60 mph, the actual MPGe was about 102. Once you get up to an 75 MPH average trip speed, the MPGe drops to 94. And by 80 MPH the MPGe drops to 77. (avg over all Tesla types)

That makes total sense. What I think most people don’t realize is that power is force times velocity and the force you need to apply to maintain a given velocity is equal to the friction plus the drag. Unfortunately, drag increases with the square of the velocity and so when you go faster you need way more power. This translates directly into increased battery drain for an EV.

The problem may be further exacerbated by the greatly increased mass of an electric vehicle and the potential for the batteries to overheat.

[edraferi]

This is why some governments raise speed limits. Faster traffic -> more energy required per mile -> more gas consumed -> more gas tax revenue

[selectodude]

Or it’s because it’s politically popular to raise speed limits since they usually raise them to the speed that is almost, but still below, the speed that everybody is already driving at currently.

[WorldMaker]

Also in the US the AAA heavily invests in lobbying for higher speed limits every year. The AAA isn't quite the villains in American politics that the NRA are (ETA: or at least, have become), but they are historically close. It's easy to forget that AAA was founded to fight speed limits in the first place.

[sizzle]

"AAA was founded to fight speed limits in the first place"

Wow never knew this is true, any sources where I can read more about this?

[WorldMaker]

I'll admit it is something of an uncharitable view. The given reason AAA was founded was to improve the "quality" of roads in the country. One of the qualities that was seen as lacking at the time was the inability to use anything close to the top speed of cars due to road hazards and pedestrians. It's related to why AAA was the first car racing body in the country, overseeing for instance early versions of the Indianapolis 500 (though it divested racing later on).

(ETA: The search term I was forgetting was "jaywalking", because AAA was instrumental in the creation of jaywalking as a crime, related to the goals of allowing faster car travel versus speed limits. https://www.salon.com/2015/08/20/the_secret_history_of_jaywa...)

[btilly]

What's most striking to me as someone who has heard over and over again about how air resistance is a X^2 property, is the extent to which short (and presumably slow) trips punch above their weight in terms of range consumed per mile. From what I can tell, the actual cost here is the fixed cost of booting up some systems and electronics, and the variable costs of running them over fewer miles can make the MPGe drop. Starting and continuing to run the AC adds up!

Two factors.

First, if you go 10% faster, air resistance may be 21% higher, but you only take 10/11 for spending 10% more energy per mile. So higher speeds cost less than you'd naively think.

Second, at low speeds we start and stop a lot. Coming to a full stop requires actually putting physical brakes on and losing energy. The heavier your car, the more that this costs you. For slower traffic, if you look at distance traveled, number of full stops and energy, I bet that you can fit a linear model in 2 variables that fits the data better and gives you a sense of how much coming to a stop costs you.

[tlb]

That's incorrect. Power consumption is proportional to drag * speed, and drag is speed^2, so power is speed^3, and energy per mile is speed^2.

[D_Alex]

Or: Work = Force * Distance, so the energy spent per mile will be proportional to drag force, which is proportional to speed^2.

Either way, its 21% increase in energy consumed per mile in this case.

[btilly]

Ah, shoot. You are right. Energy is force times distance, momentum is force times time. I was thinking about force times time.

wipes egg off of face

[carlob]

True but we're interested in power consumption per distance traveled so it goes back to O(v^2).

[sokoloff]

That’s precisely what the last clause you’re responding to says. You’re agreeing but couching it as a “but”.

[modeless]

Starting and stopping does cost energy, but regen is pretty efficient and the lesser wind resistance of slow speeds mostly makes up for it. No, davidwhodge is right, the problem with short trips has to do with the fixed costs of "warming up" the car. Just looking at the energy graph in the car while driving it's easy to see that it's much more efficient after the car has warmed up.

[kube-system]

Yes, but electric motor regen usually does not work all the way down to zero mph. Usually it stops somewhere around 5-10mph, and the friction brakes take over. Slow rolling traffic that fluctuates between something like 10-30mph is very efficient, but stop and go traffic fluctuating between 0-20mph is pretty inefficient.

[ajuc]

Additionally if you drive 10% faster you spend ~9% less time on the trip which means heating/AC is working 9% less.

[baddox]

And there’s also some “inherent” value in spending less time traveling that is more difficult to quantify.

[londons_explore]

To balance with the inherent disadvantages of more speeding tickets and a higher risk of a collision.

[m463]

I'm surprised tesla doesn't break down energy usage visually.

The nissan leaf has an energy usage display that breaks down energy into driving, climate and other systems.

http://www.nissanusa.com/vlp-assets/media/vehicles/2016/leaf...

[madaxe_again]

Air, rolling and other mechanical resistances are certainly part of the equation here, but the major driver of the decreased range at higher speeds is likely battery chemistry.

When you apply a load to a cell, the voltage sags. Heavier load, bigger sag. When a battery is operated at low voltage, it loses efficiency - the total power available decreases significantly. If you ever buy batteries for, say, building your own EV, you’ll pay a lot of attention to the C values - C1 is the capacity of the cell if it is discharged in 1 hour, C100 is the capacity at 100 hours, etc. - and there is a big difference between these values - it’s non-linear, and while the difference between C100 and C10 might be a 30% loss of available power, between C1 and C10 you’re closer to 50% - a 65% loss overall between C100 and C1.

Obviously in an EV C2-C10 are probably your most relevant numbers - but the difference in available power is significant over that range, and if you’re driving harder, putting more load on the battery, your range will be lower.

[aetherspawn]

The batteries have such large capacities that the C-rates are tiny. Tesla are well beyond the point where inefficiencies in battery contribute to as little as 1% of the total range.

Source: design engineer at EV company.

[hinkley]

Even during acceleration?

[aetherspawn]

The kind of acceleration that would cause it to be non-trivial is not the acceleration that you would use in normal driving unless you were very reckless.

[01100011]

Shower thought: It would be nice if the vehicle 'docked' to the charger at home so you could power everything up and get the climate control working before you disconnected from the grid. It's not going to make a noticable difference in mileage I'm sure, but if there is a surge at power-up I'd rather take the juice from the grid.

[caf]

It kinds of does that, because if you start the climate control while plugged in, it'll start drawing from the charger even if charging has already finished.

This is most often seen if you remotely turn on the climate control to warm the car up in the morning, when the car is still plugged in after overnight charging.

[mohaine]

And with scheduled charging you don't even have to manually do this, it just does it based on your departure time. My Model 3 is always warm and toasty by 8:30 AM M-F all winter. As someone with an unheated detached garage this is very nice. At least it was before I quit driving anywhere.

[fiddlerwoaroof]

I really need to get my wall charger installed, this would be completely infeasible with the Level 1. COVID-19 sort of messed with my plans here

[davidwhodge]

Another fun fact on practical drain vs. EPA drain:

While I love sentry mode and think it's a great feature, it keeps the electronics awake. In some cases this can cause double digit per day mileage drain. Tesla has clearly been working on this though, as the numbers have improved.

[sxp]

> What's most striking to me as someone who has heard over and over again about how air resistance is a X^2 property, is the extent to which short (and presumably slow) trips punch above their weight in terms of range consumed per mile. From what I can tell, the actual cost here is the fixed cost of booting up some systems and electronics, and the variable costs of running them over fewer miles can make the MPGe drop. Starting and continuing to run the AC adds up!

Could this be due to the battery not being at the ideal temperature on short trips? I always noticed that the efficiency of my car is lower for the first 10 miles when commuting to and from work. Since it happens in both directions, it can't be due to terrain or road type so I was guessing battery temperature.

[londons_explore]

I think there's a good chance the energy used while parked is greater than the dashboard suggests (measuring power remaining in a lithium battery is hard!). Then when you start driving, the estimate gets more accurate, and the range disappears over the next 15 minutes or so.

[davidwhodge]

This would seem totally reasonable to me. It'll take more time, but I can also dig in and see the extent of the battery heater use.

My guess is it's often cold enough for the battery to need to warm up to be efficient, but not cold enough to make it worth it to turn on the battery heater. (Your point still holds in that case)

A piece of data I happen to remember, far fewer than 10% of supercharges have the battery heater on for any period of time at all.

[r00fus]

> The data: For the hundreds of Nikola trips with an average speed of 60 mph, the actual MPGe was about 102. Once you get up to a 75 MPH average trip speed, the MPGe drops to 94. And by 80 MPH the MPGe drops to 77. (avg over all Tesla types)

My (non-Tesla) EV only gives me trip watt-hour per mile (Wh/mi)

Using an mpge to Wh/mi converter [1], 102 mgpe = about 330 Wh/mi, 94 = 385 Wh/mi and 77 = 437 Wh/mi.

My car (Ford Focus EV) gives about 275 (conservative driving) to 350 Wh/mi. It usually gives me about 80 - 130 miles range, and the stated average is 110. I get the 80 during the colder months in a warmer clime. When I was commuting into the office (pre-COVID) I was usually doing about 70-80mph.

[myself248]

> the vehicles drain some juice while parked

When we had a Tesla in the garage to install some aftermarket equipment on it, this parked power drain astonished me. Several miles PER DAY.

And we have the nerve to bother TV makers about a watt here and a watt there.

[zamfi]

> I made some graphs if anyone's curious, but I can't post them here.

I’d love to see them!

[davidwhodge]

Alrighty here's the first graph. Note that this is average speed, so any trips with an average speed near the right by definition have some parts of the trip faster than the average, so the actual drop at 80 mph isn't quite as severe as it looks.

https://imgur.com/a/c10NXaz

the reason for the cutoff is that because it's pretty hard to have a trip with an AVERAGE speed above 80mpg. It's very rare in my large dataset.

[mft_]

This is really great - thanks so much for posting! I've been hunting for a similar curve for Teslas for a while.

Can I ask:

* Which car models are included?

* You write that your methodology for this chart looks at average speed for the whole trip; if this is true, would it be feasible to apply a different methodology and divide your data up into much smaller chunks (e.g. 30 seconds) and calculate the MPGe for each chunk?

* Is there any way I could calculate a similar graph for my own car? Can I get a graph like this from your app? (I'd personally be super-interested in both being able to access my own car's curve, and also explore a 'dashboard' of the whole dataset with filters by (e.g.) model, wheel size, etc.

[modeless]

Cool! Can you make a graph quantifying the fixed costs of startup somehow? The startup costs do seem really high, to the point where it's pretty much impossible to hit the rated efficiency unless your trip is longer than 10-20 minutes to amortize the startup costs. I'm glad someone else has noticed this.

[zamfi]

Cool! Thanks. Wonder what the jump from 31-40 (ish?) is about

[davidwhodge]

I wonder that too. My guess is there's an outlier datapoint or two there messing with the average. I didn't pull out outliers.

(Since the data is smoothed, an outlier datapoint could influence speeds 2mph in each direction)

[davidwhodge]

okay I'm on it. I'll find some way to post them

[satvikpendem]

Looks like the purported range is analogous to stated phone or laptop battery life: ideal and unrealistic. This makes sense because the car is, in fact, run by a battery.

[davidwhodge]

seems like an apt comparison. Something I forgot to mention here is that the temperature also plays a huge role. I've recently started collecting more temp data, but don't have a big enough sample size to say anything definitive beyond "driving in cold weather does reduce range". This is completely expected.

As a bit of anecdata here: Parking inside vs. outside seems to have a big affect. A slightly chilly garage vs. a cold soak outdoors understandably are quite different.