I think of the question as whether you want to think of distance per unit of fuel or fuel per unit of distance.
I think both measures are sort of lacking. Because what we *really* care about are different questions:
- Do I have enough fuel to get to my destination?
- When will I need to buy fuel?
- What is my fuel cost for this trip? For this week? This month?
- What is my instantaneous fuel burn rate as a means of feedback for my driving style?
If fuel was free, would we care about MPG? Almost surely not. That's why EV buyers focus on range and not equivalent MPG. Buying fuel is a cost that is inconvenient. So if the cost is minor (EV), then we move on to the next inconvenience of how often to fuel and what that fueling event will cost me in time and/or money.
Neither fuel per unit distance nor distance per unit fuel really answer any relevant question-- they always need more information, like cost per gallon, trip distance, total distance driven in a day, week, or month, etc.
What's frustrating to me is that this incompleteness is totally ignored. I've yet to see a car's trip computer that will let you enter fuel cost like a Fuelly app or such. Gas Station apps from Exxon, Shell, etc all suck because they have they only log transactions.
With modern data tools, there's simply no excuse for not having real-time feedback on cents per mile (of the current tank), dollars per week/month, etc. Yet the best you can do is use Fuelly and manually enter all your data even though that data already exists! My Exxon and Shell apps track all the info needed in terms of transactions. Why can't the apps on my car use that info?
