Why is the efficiency lower on highways?
Comment on Tesla Cybertruck gets less than 80% of advertised range in YouTuber’s test
skysurfer@lemmy.world 10 months ago
What was the EPA rated highway range? The 320 mile range is the EPA combined city/highway which you won’t hit doing entirely highway but you would beat doing entirely city.
ABCDE@lemmy.world 10 months ago
skysurfer@lemmy.world 10 months ago
Due to electric drivetrains having minimal fixed losses at low speed unlike internal combustion engines. Aerodynamic losses start becoming the largest factor for EVs at relatively low speeds (25-35 MPH) since other losses at so low. This shows up on tests as higher city efficiency and lower highway.
For an internal combustion engine you are burning a large amount of energy just to keep the engine running, so the slower the speed, the less distance traveled for the fixed amount of running losses and lower the MPG. It isn’t until higher speeds (55-65 MPH) that aerodynamic losses become the largest factor. This manifests as lower efficiency in the city tests and higher highway.
Nollij@sopuli.xyz 10 months ago
It’s also a factor that acceleration/deceleration in an ICE kills mileage. Highway tests maintain a constant speed. If you ran the same test at 35 mph, they would get much better mileage than at 55 (or 70)
flyingjake@lemmy.one 10 months ago
Idle losses are real but not very substantial in a modern engine compared to the bigger factor you’re missing which is that in city driving tests there is a lot of speeding up and slowing down, ICE vehicles throw away all the energy used to slow down as heat in the brakes which makes city cycles particularly inefficient while an EV captures that energy through regenerative braking, dramatically reducing the net cost of those momentum changes.
snowe@programming.dev 10 months ago
Regenerative braking only can recapture something like 2-5% of lost energy. The bigger factor is exactly what the other person said.
skysurfer@lemmy.world 10 months ago
Ah, good point, the speed changes for ICE ended results in lots of energy wastes due to heat instead of being recaptured. That would certainly be the largest loss for an ICE in the city cycle.
ABCDE@lemmy.world 10 months ago
That makes sense, thanks.
Critical_Insight@feddit.uk 10 months ago
It has the aerodynamics of a brick
TheIllustrativeMan@lemmy.world 10 months ago
So does the EV9, but it exceeded the EPA range in the same test.
Critical_Insight@feddit.uk 10 months ago
This was a highway test though, not how EPA test the ranges
ABCDE@lemmy.world 10 months ago
Aha yes, but what about other EVs?
statue_smudge@lemmy.world 10 months ago
There’s more air resistance at higher speeds.
ABCDE@lemmy.world 10 months ago
That doesn’t explain why ICE vehicles are much better efficiency-wise than EV ones at higher speeds, just why EVs don’t do so well. Another post responding to me addresses it well.
Nollij@sopuli.xyz 10 months ago
Do you mean that ICE is more efficient than EV at higher speeds, or that ICE scales better than EV?
WaterWaiver@aussie.zone 10 months ago
Aerodynamic drag increases with the square of speed. All cars have a different optimum speed for maximum range (which depends on wind speed & temperature too).
eatfudd@lemm.ee 10 months ago
Air drag
TheIllustrativeMan@lemmy.world 10 months ago
Most EVs he’s tested hit or exceed the EPA range on this test. Even bricks like the EV9 exceed their EPA range in similar temps.