For what it's worth, my car's fuel gauge appears to do exactly this—no change from full for the first 60-100 miles, and about 2.5 gallons left on "empty." The first quarter tank lasts a good deal longer than the third, at least according to the gauge.
You'd think you wouldn't want to do this with a range estimation because the error's more obvious, but I'm also sure they don't want to sandbag its estimate from a full charge because people will be wondering why they're not seeing the advertised range. I'm sure they do want the car to be able to keep going a little past empty, though, and those spare miles have to come from somewhere.
I was surprised how much of a buffer modern Mazdas keep. The "range" is based on 2 gallons hidden. At 3 gallons remaining, it appears as if you have 1 gallon remaining (i.e. 25-35 miles depending on your average gas mileage since the last reset.) So "0 miles remaining" happens when you really could go another 50-70 miles.
This is based on the total gas tank size compared to how much it takes to fill, but also because I'm stubborn and have pushed it several miles past "0" out of curiosity (but not regularly, as I have no wish to overheat my fuel pump or run out of gas!)
> It's also possible that it keeps a buffer of ~1 gallon of gas that it never tells us about, when quoting the total range, and it eats into this buffer without telling us.
This is quite likely. My car supposedly has an 11-gallon gas tank, and if I refuel right when I hit 0 miles remaining then it only takes 10 gallons of fuel to fill the tank.
or, you could estimate it fairly accurately using the following formula:
(fuel tank capacity - gallons needed to fill tank when gas light turns on) * (average miles per gallon)
I have about 4 gallons left when the light turns on. 2 gallons left when the needle dips below the "empty" line. The emptiest my tank has ever been is 0.5 gallons left.
“It's also possible that it keeps a buffer of ~1 gallon of gas that it never tells us about, when quoting the total range, and it eats into this buffer without telling us.”
I am fairly confident that something similar is happening with my Honda. I thought I was going to run it dry, but then it just sat at 10 miles remaining for at least another 15-20 miles before I reached a station.
Only because they don't need it. Most people are comfortable with a ~300 mile range, knowing they can refill in 5 minutes. So most cars are built with 10-to-15 gallon tanks.
Build a car with a 30 gallon tank and you could easily be in the neighborhood of 1000 miles range.
> In a Mercedes [...] the tank is really empty as soon as the needle hits 0
Not in mine (in Germany, recent C class). It depends a bit on whether you define "reserve level" as 0 or not. On the one hand, the needle does go below reserve level all the way to physical zero, but from a UI point of view, reserve level itself is clearly what they want you to see as "running on empty". And that's what they mean in this article, too.
In my car, it actually shows you in the dashboard how much range you got left based on your current driving style, too. I have a medium-power Diesel engine, so that works out to about 40 miles remaining once the warning light goes on, and that's pretty accurate. After half of that is used up, the dashboard stops showing the estimate and instead begins to flash a "fill up immediately!" message.
Most cars keep a little gas under 0 miles left in order to preserve the fuel pump. If you run a car out of gas completely in a modern car, you can cause a lot of damage to the fuel system.
I have a 2014 Nissan Altima. It gets better gas mileage than any vehicle I've ever driven, other than motorcycles. On long highway/interstate trips, I get 550-600 miles on a tank of gas (the tank holds about 12 or 13 gallons, if memory serves).
My girlfriend has been driving it for the last year or so and the only times I drive it anymore is to take it in for an oil change or maintenance, but I often check the statistics and it averages 34 mpg overall (most of her driving is highway). The "low fuel" indicator in it also comes on with somewhere around 100 miles remaining.
I did drive it far enough once without stopping for gas that the "miles left" indicator read "---". I was about 10 minutes from home and figured I'd chance it (there's a gas station at the intersection where I turn off the highway to come home). My thought was that if I had designed the "countdown indicator", I would be in a bit of a buffer so that the car doesn't actually die going down the road when it hits zero, so I was certain I still had enough gas left to make it.
My truck (large 2013 Dodge Ram) averages right about half of that. Its "low fuel" indicator comes on with about 50 miles remaining. The Harley gets around 50 mpg (and offers to find the nearest gas stations when there is ~35 miles remaining).
A typical person knows how many gallons their gas tank can hold, and thus how far they can go without needing to refuel. For day to day driving, it doesn't really matter. For long road trips, it can be essential if you're on an extended barren interstate highway.
The specific amount of fuel in the tank is a number that I would think most people wouldn't really care about.
Some cars will give you calculated "miles/km till empty" based on average mpg calculations, which is arguably at least a semi-useful metric. My car gives me a vague gauge until I get close to zero, and then it gives me a marginally more accurate countdown from 1.0 gal to zero.
I think the reason that most fuel gauges are so vague is that fuel levels rise and fall pretty erratically, which would make a very specific gauge give you bad information at least as often as it would give you good. Fuel levels are usually measured with some type of float, and depending on if you were travelling or parked on an incline the float could register a fairly large swing.
In an old Honda I drive once in a while I could see the fuel gauge swing more than 1/8 of a tank depending on what direction I parked it on my sloping driveway (nose down or nose up).
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