Why does fuel economy get better on the highway, but EV range gets worse?
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Many answers focus on RPMs of engines, that’s not really important. Lemme explain
Wind resistance is the number one thing slowing down a car. If you took away that, they would continue roll on a flat road for a very long time. It’s actually such a big factor that you could just say the wind resistance experienced = the power or effort needed from the engine to maintain the speed.
Importantly, wind resistance goes up dramatically with higher speed. At 50mph your wind resistance isn’t twice what it is at 25mph, it’s actually about 4 times as much. (Velocity is squared in the wind resistance equation)
Knowing this, you would figure that the faster you go, the worse fuel economy. This is true with electric cars! Because they are so simple.
More speed
More wind resistance
More power input to the electric motor to overcome the wind resistance
Non EV cars is where it gets complicated…
Now many of these answers focus a lot on the fact that engines like to run at a certain RPM.
That’s not too important to this question…
Whether puttering along at 25mph or cruising at 75mph, modern cars are going to use gears to find a nice happy efficient RPM.
Both gas and electric cars are going to have similar drops in efficiency speeding up from 65mph to 75mph.
The big difference is in city driving. Gas cars are TERRIBLE at city driving. Electric cars are fantastic.
Electric cars aren’t bad on the highway, gas cars are just really bad in the city. So bad that many cars use similar amounts of gas (say like 18mpg versus 20mpg, not a big difference usually) to putter around a city with hardly any wind resistance, versus to scream down the highway with a ton of it.
There are 4 things a car can be doing:
Not moving
Coasting
Slowing down
Speeding up
In a gas car:
Not moving: slow burn of gas
Coasting: slow burn of gas
Slowing down: slow burn of gas
Speeding up: big burn of gas
In an electric car:
Not moving: near zero energy usage
Coasting: near zero energy usage
Slowing down: regenerating energy
Speeding up: using energy
You’ll find when you look at city driving, probably only about 10-20% maximum of your drive are you doing the only thing that uses energy in an EV: speeding up.
And as a bonus, you can recapture some of that energy (with substantial losses) during the portion of time when you’re slowing down.
The gas car burns gas from the moment it turns on to the moment it turns off. And wastes any forward momentum as heat in its brakes.
So while the engine is on, you better hope you’re covering miles at high speeds, because it’s not that different than sitting around in traffic.
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