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> Don't get me started on cars that display usage in kWh/h per 100km. Yes, you read that right. ICEs use litres per 100km which I think is where this comes fro

> Don't get me started on cars that display usage in kWh/h per 100km. Yes, you read that right. ICEs use litres per 100km which I think is where this comes from. And I hate it. miles-per-gallon is much easier to understand I think. I wish we could have split the difference in the EU and just had km-per-litre. I'd rather know how far a tank will get me than how much fuel I'll use to travel exactly 100km

Cyykratahk 3y ago
The biggest problem with MPG is its inverse nature makes it a bad unit to use to compare cars. A 20 MPG car is not twice as efficient as a 10 MPG car. http://www.mpgillusion.com/p/what-is-mpg-illusion.html http://www.mpgillusion.com/p/what-is-mpg-illusion.html L/100km has the length and volume units reversed, which allows comparisons.
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- Goz3rr 3y ago
  A 20MPG (11.76 l/100km) car is twice as efficient as a 10MPG (23.52 l/100km) car though? The issue is going from 30 to 20MPG is not the same change as going from 20 to 10MPG, where as the difference between 15 and 10, and 10 and 5 l/100km is the same absolute change.
- vegardx 3y ago
  I might be hung up on the word "illusion". The only difference between miles per gallon and gallons per mile is that the former increases and the latter decreases with efficiency. They are still saying the exact same thing.
  - shanebellone 3y ago
    "They are still saying the exact same thing." They are but now I prefer .05 GPM to 20 MPG.
    - vegardx 3y ago
      I do as well. Everyone in the US it seems to like bigger numbers. Just look at the argument some people use to why some people prefer Fahrenheit over Celsius. ... is what I would say, but Tesla seems to be the only one using the sensible Wh/m or Wh/km. All the German ones use the nonsensical kWh/h per 100km.
      - shanebellone 3y ago
        In fairness, 0 being cold and 100 being hot is pretty intuitive. I would be curious to know how people raised on Celsius feel about Fahrenheit after having lived with it long-term.
- pflanze 3y ago
  > A 20 MPG car is not twice as efficient as a 10 MPG car. Why not? The page you linked doesn't talk about "twice as efficient", it talks about an absolute number of gallons saved per distance travelled. Also, assuming there was no typo, vegardx's point was that "kWh/h per 100km" is invalid. "kWh/h" is the same as "kW", and "kW per 100km" (power per distance) is not describing vehicle efficiency, it's non-sensible. "kWh per 100km" (energy per distance) is.
justeleblanc 3y ago
> And I hate it. miles-per-gallon is much easier to understand I think. It's just something you're used to. > I'd rather know how far a tank will get me than how much fuel I'll use to travel exactly 100km Well, there you go, you're comparing apples to oranges. Unless your tank is exactly one gallon, you've made a conversion when you compute how far a tank will get you. Well, we do the same thing here. I want to travel 500 km? I'll multiply my L/100km by 5 and get how much gas I need. This tells me how many times I'll have to refuel, etc.
- bartislartfast 3y ago
  true I guess. maybe its just something I'm used to. distance-per-fuel-amount just seems intuitively more useful to me than fuel-amount-per-distance, even if they're two sides to the same coin
rektide 3y ago
I think it'd be incredibly valuable if all vehicles could pick one common unit. Personally I think that need dominates all others. And it suggests to me MPGe is the way to go in the states, to the extend that it makes me want EV "fuel" gauges to be "gallon-equivalents" (33.7kWh). Yes your car only has 2~3 gallons of gas capacity, that's because it's badass & efficient. This is of course (imo: alas) never going to happen. I think the actual units used in EU are, for example, 19kWh/100km (from the BMW iX which does very well for it's size-class). You seem to have an extra /h in your figure. It has the advantage of being a understandable number, relatively well sized in scope. People can think of 100km as a reasonable length in their head that connects distant points. We tend to think in terms of kWh, which is what electricity is typically metered in world wide. It feels like a poor use of a metric system that shouldn't have a bunch of weird prefixes (there's a k above & below the divisor? are you kidding me? 100km? c'mon!!) but the units are people-sized, are things we can work with in our head. And the final number, 19, as in 19 kWh/100km, is reasonably scoped, going up if you're more efficient, going down if you're less efficient. It's inverse from MPG, putting the range-unit is on the bottom & the energy-unit is on the top. Some people love it: they claim that the difference between like 12 & 24 MPG is hard to appreciate the savings off of, whereas the difference between 24 & 48 MPG looks big but is actually only half as much fuel saved. Personally, I don't really chalk this up as a win, but some people think it's important & I can recognize that potentially it might be helpful. I still think we should just use 33.7kWh / 1 gallon-of-gas equivalent as the common unit of energy & give everyone a common frame of reference.
- vegardx 3y ago
  Some German cars display current usage as kWh/h, which is just a stupid way of saying kW. If you're using 3kW for one hour, that means you're using 3kWh ... per hour. It just doesn't make any sense to write it like that. They correctly display the average usage over a given distance as kWh/100km. There's a lot of fuzz in the EV space since everyone is advertising WLTP (previously NADC) numbers as an indicator for range. It uses a standardized test, so this means the numbers should be comparable. But they're not. Some BEVs are much more efficient in cold weather than others, due to things like heat pumps or just better engineering, like aerodynamics. This isn't well reflected in WLTP, and people get disappointed. You can easily argue for both kWh or Wh. I've always been a proponent of using the smallest units possible, since then everything is just addition, regardless of what you want. With everything being in units of 10, it's fairly easy to do, either way. You could argue that the logical conclusion would be to use Ws/m, which is just ... Joules/m, another SI unit. But then we're using units that most people have no fundamental understanding of.
ilyt 3y ago
It would be worthy sacrifice to get rid of miles. Now let's talk about wheel size. mm/percentage/inches all in one unit...

Cyykratahk 3y ago

The biggest problem with MPG is its inverse nature makes it a bad unit to use to compare cars. A 20 MPG car is not twice as efficient as a 10 MPG car. http://www.mpgillusion.com/p/what-is-mpg-illusion.html http://www.mpgillusion.com/p/what-is-mpg-illusion.html L/100km has the length and volume units reversed, which allows comparisons.

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Goz3rr 3y ago
A 20MPG (11.76 l/100km) car is twice as efficient as a 10MPG (23.52 l/100km) car though? The issue is going from 30 to 20MPG is not the same change as going from 20 to 10MPG, where as the difference between 15 and 10, and 10 and 5 l/100km is the same absolute change.
vegardx 3y ago
I might be hung up on the word "illusion". The only difference between miles per gallon and gallons per mile is that the former increases and the latter decreases with efficiency. They are still saying the exact same thing.
- shanebellone 3y ago
  "They are still saying the exact same thing." They are but now I prefer .05 GPM to 20 MPG.
  - vegardx 3y ago
    I do as well. Everyone in the US it seems to like bigger numbers. Just look at the argument some people use to why some people prefer Fahrenheit over Celsius. ... is what I would say, but Tesla seems to be the only one using the sensible Wh/m or Wh/km. All the German ones use the nonsensical kWh/h per 100km.
    - shanebellone 3y ago
      In fairness, 0 being cold and 100 being hot is pretty intuitive. I would be curious to know how people raised on Celsius feel about Fahrenheit after having lived with it long-term.
pflanze 3y ago
> A 20 MPG car is not twice as efficient as a 10 MPG car. Why not? The page you linked doesn't talk about "twice as efficient", it talks about an absolute number of gallons saved per distance travelled. Also, assuming there was no typo, vegardx's point was that "kWh/h per 100km" is invalid. "kWh/h" is the same as "kW", and "kW per 100km" (power per distance) is not describing vehicle efficiency, it's non-sensible. "kWh per 100km" (energy per distance) is.

justeleblanc 3y ago

> And I hate it. miles-per-gallon is much easier to understand I think. It's just something you're used to. > I'd rather know how far a tank will get me than how much fuel I'll use to travel exactly 100km Well, there you go, you're comparing apples to oranges. Unless your tank is exactly one gallon, you've made a conversion when you compute how far a tank will get you. Well, we do the same thing here. I want to travel 500 km? I'll multiply my L/100km by 5 and get how much gas I need. This tells me how many times I'll have to refuel, etc.

bartislartfast 3y ago
true I guess. maybe its just something I'm used to. distance-per-fuel-amount just seems intuitively more useful to me than fuel-amount-per-distance, even if they're two sides to the same coin

rektide 3y ago

I think it'd be incredibly valuable if all vehicles could pick one common unit. Personally I think that need dominates all others. And it suggests to me MPGe is the way to go in the states, to the extend that it makes me want EV "fuel" gauges to be "gallon-equivalents" (33.7kWh). Yes your car only has 2~3 gallons of gas capacity, that's because it's badass & efficient. This is of course (imo: alas) never going to happen. I think the actual units used in EU are, for example, 19kWh/100km (from the BMW iX which does very well for it's size-class). You seem to have an extra /h in your figure. It has the advantage of being a understandable number, relatively well sized in scope. People can think of 100km as a reasonable length in their head that connects distant points. We tend to think in terms of kWh, which is what electricity is typically metered in world wide. It feels like a poor use of a metric system that shouldn't have a bunch of weird prefixes (there's a k above & below the divisor? are you kidding me? 100km? c'mon!!) but the units are people-sized, are things we can work with in our head. And the final number, 19, as in 19 kWh/100km, is reasonably scoped, going up if you're more efficient, going down if you're less efficient. It's inverse from MPG, putting the range-unit is on the bottom & the energy-unit is on the top. Some people love it: they claim that the difference between like 12 & 24 MPG is hard to appreciate the savings off of, whereas the difference between 24 & 48 MPG looks big but is actually only half as much fuel saved. Personally, I don't really chalk this up as a win, but some people think it's important & I can recognize that potentially it might be helpful. I still think we should just use 33.7kWh / 1 gallon-of-gas equivalent as the common unit of energy & give everyone a common frame of reference.

vegardx 3y ago
Some German cars display current usage as kWh/h, which is just a stupid way of saying kW. If you're using 3kW for one hour, that means you're using 3kWh ... per hour. It just doesn't make any sense to write it like that. They correctly display the average usage over a given distance as kWh/100km. There's a lot of fuzz in the EV space since everyone is advertising WLTP (previously NADC) numbers as an indicator for range. It uses a standardized test, so this means the numbers should be comparable. But they're not. Some BEVs are much more efficient in cold weather than others, due to things like heat pumps or just better engineering, like aerodynamics. This isn't well reflected in WLTP, and people get disappointed. You can easily argue for both kWh or Wh. I've always been a proponent of using the smallest units possible, since then everything is just addition, regardless of what you want. With everything being in units of 10, it's fairly easy to do, either way. You could argue that the logical conclusion would be to use Ws/m, which is just ... Joules/m, another SI unit. But then we're using units that most people have no fundamental understanding of.

ilyt 3y ago

It would be worthy sacrifice to get rid of miles. Now let's talk about wheel size. mm/percentage/inches all in one unit...