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Comment by snovv_crash | Hacker News Reader

The majority of the miles were highway miles, so for a big boxy vehicle this is expected IMO.

Typically, the fuel source, be it a gas tank or battery, would be sized appropriately based on the car/truck it’s in to get fairly consistent range with typical vehicles in the same class.

If the Cybertruck is big and boxy, I would expect the battery to be large enough to compensate for that, so range is compatible to other vehicles (300+ miles per charge).

It also weighs 3 tons which is probably the main factor. A Model 3 towing 1 ton will barely get 100 miles range.

That said, despite the boxy look, the Cybertruck has a respectable 0.34 aerodynamic coefficient, not far from 90s sedans.

That 0.34 is applied to a huge frontal area though. Ends up having lot more drag then a sedan because the truck needs to move a lot more air molecules out of the way.

(FTR, I jumped the gun on my answer and I was wrong - the actual relevant performance figure is the product of the coefficient times the frontal area, so the parent is correct, it might perform much worse in practice than a smaller car with the same CD)

That's not how it works. A car's drag coefficient is calculated in a wind tunnel, and takes into account the entire body shape.

The frontal area can also be very deceiving, a new VW ID Buzz for example has a CD of 0.285 despite a massive front.

Weight has very little impact on range

Afaik most car manufacturers determine their advertised mileage based on highway drives at an average speed, because stop and go driving consumes more fuel. I would think this would literally be the ideal case for their car, even if it is boxy.

Can't speak for everyone, but my expectation was bigger car = bigger battery = longer range. If aerodynamics are that much of a factor, then electric pickup trucks are doomed to be rich people toys until we get better batteries.

If you do the math for power to maintain a given speed, you'll see an exponential curve. Air drag starts to dominate the energy budget very quickly. Anything you can do to minimize drag (don't carry aftermarket accessories, follow cars) will help tremendously.

Highway miles are generally the most efficient miles for a vehicle because there's less energy wasted in slowing and speed changes, at least for gasoline cars though I imagine the same factors are present in electric vehicles minus maybe the braking losses since they can use regenerative braking. Is that alone enough to make city more efficient for electric vehicles?

edit: Just judging from my own observations (and the EPA estimated differences) I get way better mpg when I take long drives on the highway cruising at 65-70 than I do on periods with mostly city driving. I keep track when I fill up as a check against the car's slightly wonky mpg calculation and it's a difference of 5ish mpg more for highway like the EPA estimates suggest.

For EV cars(1), air drag is the highest range killer. There's a huge difference in range depending if you go 65, 70 or 80. And if you follow cars or push the air by yourself.

Stop and go doesn't really impact range that much, and the low overall speed is a better regime. Although these cars accelerate like crazy so it's hard to resist the pedal when doing stop-and-go.

(1) in fact for all cars, but ICE cars are so inefficient in other regimes that air drag is not a prominent problem until much higher speeds.

Not the case for electric. Batteries are heavy, and it takes more current to maintain a faster speed than a slower speed. Plus as you point out you don't get as much regenerative breaking.

You can see this in regular gas hybrids that get better city mileage than highway mileage. The effect is even more pronounced in full electric vehicles.

The weight of the battery won’t affect the energy needed to keep a car at a steady highway speed. The energy needed is just whatever losses come from friction, air resistance, etc

At 70mph most energy is lost to wind resistance.

EVs are also heavier, which increases rolling resistance on the tires. This lead to the formulation of stiffer tires for EVs to counteract that effect.

The weight of the battery is related to the amount of friction.

> Plus as you point out you don't get as much regenerative breaking

Regenerative breaking is not a benefit compared to steady driving, it's a waste of energy due to the second law of thermodynamics.

It's only a benefit when you compare it to non-regenerative breaking.

Yes. When I had a Nissan Leaf for a couple of months, I couldn't make it to the office and back without a partial recharge on the way home. But I discovered if I got off at an exit fifteen miles earlier than normal and took surface streets, I could make it home with a bit of capacity to spare. That's not something that would have been good for the battery if I did it every day but at the time I was going into the office about once a week so it worked out fine. Plus I was using the 110V charger at home, which would take more than the next morning to charge the battery fully.

The biggest loss at highway speeds is actually wind. I think wind resistance goes up with the cube of speed.

As a result, electric cars are more efficient in typical city driving. You can see it in the MPG stickers , which are higher in city than highway for EVs

For gas cars, their most efficient speed is typically a steady 35-40 mph. For an electric, it’s 15-20. If there were no wind resistance both these numbers would be substantially higher.

No, the best MPG is at 30-40 mph with ICE vehicles due to auxiliary loads and losses at lower speeds and wind at higher.

I would guess BEVs have their breaking point at even lower due to lower idle power losses.

If you can maintain constant speeds it would be but the only places I drive in that range is in cities where I'm stopping and starting a lot so the wasted energy there dominates. I keep rough track of my mpg each time I fill up (as a sanity check to the calculated MPG my car gives me) and when I take long trips home I easily hit 33-34 mpg while weeks where its mostly short trips in the city I usually get more around 28 or lower. And those long trips sit at 60-70 for an hour or more at a time in good traffic.

Ye that is correct.

My commute is about 10 miles of which 8 is 40 mph two lane country road. So I think I got about the lowest mpg my car can have.

Once you hit 65mph and above your gas mileage and electric wh/mi drop like a rock due to air resistance scaling non-linearly.

I get way better mpg when I take long drives on the highway cruising at 65-70 than I do on periods with mostly city driving. I keep track when I fill up as a check against the car's slightly wonky mpg calculation and it's a difference of 5ish mpg more for highway like the EPA estimates suggest.

(mi/wh drops. wh/mi increases.)

Rocks slow down due to air resistance :-)

Drops like a meteor?

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