Yeah, most of the time when someone talks to me about gas mileage, they're interested in better mileage in order to save money or conserve gas, not to go further between fill-ups. So phrasing it as a 33% vs 18% savings hides that you actually save more gas, and so more money, going from 14 to 17 than 33 to 50.

That's one question ,but another one is:

How far can I drive per $100?

When looking at the car in part for discretionary uses, that's a valid question.....

> That's one question ,but another one is:

That is a question I've never seen anybody ask in my whole life. There are precious few people who drive for the sake of driving, for the vast majority driving is utility to go from point A to point B.

Therefore, why optimize for the significantly less common (almost irrelevant, even) case of "I've got money burning my pocket, how far can I drive?"

"how far can I drive for this amount of $" is a question I've only heard a few times. But I do often hear "how far can I drive on a tank" or "how far can I drive on my remaining amount of fuel".

Perhaps the disconnect we see in this comment thread is between people who do almost entirely city driving and people who drive long distances. If you only ever drive a few miles at a time, you don't really care what sort of distance you can manage on a tank, you just care how much it's going to cost you to go to work every day (you'll probably convert the fuel/distance ratio into a money/time ratio.) If you spend a lot of time driving across central Kansas, how often you have to stop for gas becomes a more significant consideration (you'll probably convert distance/fuel into stops/time.)

How often you stop for gas is surely better covered by a "range" measurement for the car? Maybe it's different in the states, but all the cars I've ever been in show your remaining fuel as a fraction of a tank. In that case, volume of fuel is completely irrelevant, so MPG vs liters/100km has not place. e.g. My tank takes me 400 miles => I have half a tank left => I can go another 200 miles ...is exactly equivalent to... My tank takes me 600 km => I have half a tank left => I can go another 300 km

(For the purposes of this post, 1 mile = 1500m. If the size of a gallon changes with locale, why not a mile? :-p )

> Perhaps the disconnect we see in this comment thread is between people who do almost entirely city driving and people who drive long distances.

That's an interesting thought, and it probably has more than a grain of truth.

Maybe. I tend to live in rural areas so maybe that's a factor.

But I was more thinking of this:

"We have a vacation budget of X for a weekend trip. We don't want to spend more than Y for gas. What options do we have?"

The difficulty with this is the widely varied price of gasoline. If we assume $4/gal, $100 would buy us 25 gallons of fuel, so we can just multiply those 25 gallons by the MPG:

  MPG = Miles per $100 (MPG*25/$_per_gallon)
  14 = 350
  17 = 425
  33 = 825
  50 = 1250