4 ms·

Your Prius is in another galaxy regarding safety and infotainment, that’s why. Also likely cruise speed in 1939 was much slower, and drag is a function of velo

Your Prius is in another galaxy regarding safety and infotainment, that’s why. Also likely cruise speed in 1939 was much slower, and drag is a function of velocity^2

jjtheblunt 5y ago
> drag is a function of velocity^2 i have to explain that to (fellow but new) EV drivers, that blasting down a highway at high speed for a fixed distance seems to drain the battery, because of drag, far more than travelling the exact same distance at slow speed. I still feel like i've not sorted out the equations involved.
- deelowe 5y ago
  I did an experiment on the interstate and drove at highway speeds to see if the mpg was comparable. It wasn't, so there's definitely another factor there. Here they cut groves in the concrete pavement on the interstate where as the highways are smooth asphalt. I've wondered if maybe rolling resistance is also a factor here. It was a pretty huge difference. Like more than 10% IIRC.
  - Tade0 5y ago
    I don't have reliable numbers on this, but rolling resistance appears to be the main factor up to about 60-80km/h, above which drag takes its place. Looking at the fuel consumption in my hybrid it's around 50-60% higher at an average speed of 100km/h than at 70km/h. The difference would have been 2x if was just due to drag.
  - toast0 5y ago
    For EVs it's pretty simple, the faster you go, the more power you use, and the more air resistance, and the less miles / kWh. The more power you use, the more power is lost in wiring, the hotter the batteries get and less efficient they are, etc. There's probably some minimum efficient speed, but as you go faster, everything works against you to make things less efficient. For gas engines it's quite a bit trickier, because a hotter engine gets more complete combustion and more power out the driveshaft per gallon (also more NOx, see VW) and there's a small range of RPMs where power output is best, combined with a transmission gear where efficiency is best, combined that gets you a target speed for best fuel to power at the wheels. But air resistance does get worse as you go faster. So you've got some things pushing you to go faster (sometimes much faster), and other things pushing you to go slower.
    - mnw21cam 5y ago
      You can get the same effect with a "gas" engine by having a smaller engine and going at a slower speed.
    - jacquesm 5y ago
      > there's a small range of RPMs where power output is best The so called 'power band'.
    - deelowe 5y ago
      My point was that at the same speed, the freeway uses more energy than the highway. There's more to it than just wind resistance in my area at least.
- mhh__ 5y ago
  Does the car have a power usage estimator? Or would that perhaps be dangerous if one misses traffic changes due to following the dial
  - jjtheblunt 5y ago
    7+ years old BMW i3 so yes it does.
- kingkongjaffa 5y ago
  The equations of motion and power usage due to drag and rolling resistance for vehicles are well understood: see: http://thecartech.com/subjects/auto_eng/car_performance_formulas.htm http://thecartech.com/subjects/auto_eng/car_performance_form...
  - jjtheblunt 5y ago
    thanks as i had not known proper terminology to search for that
aliswe 5y ago
this one topped 139km/h ... my prius is capped 180 :')

Your Prius is in another galaxy regarding safety and infotainment, that’s why. Also likely cruise speed in 1939 was much slower, and drag is a function of velocity^2

jjtheblunt 5y ago

> drag is a function of velocity^2 i have to explain that to (fellow but new) EV drivers, that blasting down a highway at high speed for a fixed distance seems to drain the battery, because of drag, far more than travelling the exact same distance at slow speed. I still feel like i've not sorted out the equations involved.

deelowe 5y ago
I did an experiment on the interstate and drove at highway speeds to see if the mpg was comparable. It wasn't, so there's definitely another factor there. Here they cut groves in the concrete pavement on the interstate where as the highways are smooth asphalt. I've wondered if maybe rolling resistance is also a factor here. It was a pretty huge difference. Like more than 10% IIRC.
- Tade0 5y ago
  I don't have reliable numbers on this, but rolling resistance appears to be the main factor up to about 60-80km/h, above which drag takes its place. Looking at the fuel consumption in my hybrid it's around 50-60% higher at an average speed of 100km/h than at 70km/h. The difference would have been 2x if was just due to drag.
- toast0 5y ago
  For EVs it's pretty simple, the faster you go, the more power you use, and the more air resistance, and the less miles / kWh. The more power you use, the more power is lost in wiring, the hotter the batteries get and less efficient they are, etc. There's probably some minimum efficient speed, but as you go faster, everything works against you to make things less efficient. For gas engines it's quite a bit trickier, because a hotter engine gets more complete combustion and more power out the driveshaft per gallon (also more NOx, see VW) and there's a small range of RPMs where power output is best, combined with a transmission gear where efficiency is best, combined that gets you a target speed for best fuel to power at the wheels. But air resistance does get worse as you go faster. So you've got some things pushing you to go faster (sometimes much faster), and other things pushing you to go slower.
  - mnw21cam 5y ago
    You can get the same effect with a "gas" engine by having a smaller engine and going at a slower speed.
  - jacquesm 5y ago
    > there's a small range of RPMs where power output is best The so called 'power band'.
  - deelowe 5y ago
    My point was that at the same speed, the freeway uses more energy than the highway. There's more to it than just wind resistance in my area at least.
mhh__ 5y ago
Does the car have a power usage estimator? Or would that perhaps be dangerous if one misses traffic changes due to following the dial
- jjtheblunt 5y ago
  7+ years old BMW i3 so yes it does.
kingkongjaffa 5y ago
The equations of motion and power usage due to drag and rolling resistance for vehicles are well understood: see: http://thecartech.com/subjects/auto_eng/car_performance_formulas.htm http://thecartech.com/subjects/auto_eng/car_performance_form...
- jjtheblunt 5y ago
  thanks as i had not known proper terminology to search for that

aliswe 5y ago

this one topped 139km/h ... my prius is capped 180 :')