7 ms·

> My 2016 ICE car's "miles left" meter is accurate to +/- 2 miles from the moment I top up the tank (80% highway driving, 20% hilly city and rolling country roa

by mwint 3y ago

> My 2016 ICE car's "miles left" meter is accurate to +/- 2 miles from the moment I top up the tank (80% highway driving, 20% hilly city and rolling country roads). No way. That’d be accurate to under 1% - well within the variation you’ll get just from different air densities (temperature, pressure, humidity). Forget about A/C on or off, tire pressure, etc. It’s gotta be tricking you somehow.

gen220 3y ago
We regularly do road trips of 200+ miles, and we get 350 miles on a full tank of gas. At the beginning of the trip, the GPS will say something like "250 miles to your destination" and the car will say "180 miles left" I regularly pull off the highway to fill up with around "20 miles" left, when there are ~90 miles left in the trip (e.g. it was dead-on accurate for the last 160 miles), according to the GPS. I agree that it's spooky. I think, when making estimates for "miles left", our car must be doing some calculation like (rolling estimate of mpg) * (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. There's certainly a bunch of tricks they could be pulling off. The point is, from a driver's point of view, I have a trustworthy number. If they need to pull off some tricks to achieve that trustworthiness (e.g. low-balling total range), that's OK with me. With EVs, "total range" is a marketing term, so they have a strong incentives to fib about it. Unfortunately, this makes the vehicles worse to operate.
- germinalphrase 3y ago
  “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.
  - vdqtp3 3y ago
    Most Honda models have a ridiculous reserve, something like 3.5 gallons. I still regret informing my mother of this fact...she never ran out of gas until I did.
- unregistereddev 3y ago
  > 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.
hot_gril 3y ago
Maybe it gives the user an underestimate then wastes gas later to meet it? :D
mrguyorama 3y ago
Fun thing about a car: They have computers that measure all those factors! Your engine knows the air density, air temperature, the rough gravity vector (used for things like hill start assist), lots of info on tire performance, speed, fuel flow, etc etc etc, with more modern cars getting things like GPS details. The estimate they use for range is based on the average fuel economy you get, not some fake model made by the EPA that doesn't represent reality. This has been true in Toyotas since at least 2004, so I would hope it could be true for a "Luxury" car from a "tech" company.
- mwint 3y ago
  It doesn’t measure those factors in advance.
  - mrguyorama 3y ago
    It doesn't have to. It measures them in real time, and can integrate over time. Astronomers also don't see into the future but some basic calculations can let them make very accurate predictions about where the planets will be in a month. What the heck is your point?
    - mwint 3y ago
      Okay, so if I give you all the data from my car, and say it has 10.3 gallons of gas, you’re telling me you can predict how many miles it will go to within a percent? No, you can’t. Because I might go uphill or downhill. It might rain. It might be hot or cold. The car is doing something tricky (aka lying) as discussed above.
      - gen220 3y ago
        I think if you gave us a hidden buffer of 1 gallon (i.e. we actually have 11.3 gallons, but I report that you have 10.3 gallons, and selectively burn some of that buffer without reporting it), and you drive in conditions that fit within the footprint of your prior 3000 miles of driving history, yeah we probably could guess within a percent. To the best of my understanding, this is what most modern ICE cars do when they give you the "miles remaining" metric. I don't know how else they could be so outwardly accurate. This falls under the category of "trick", but it's actually a trick that helps me by allowing me to plan my trips better. Giving the "current estimate of actual miles remaining", as a multi-variate function of all the things you mention, is actually less helpful and more stress-inducing – even while it's technically providing more information, it's information that isn't very helpful.

by mwint 3y ago

gen220 3y ago

We regularly do road trips of 200+ miles, and we get 350 miles on a full tank of gas. At the beginning of the trip, the GPS will say something like "250 miles to your destination" and the car will say "180 miles left" I regularly pull off the highway to fill up with around "20 miles" left, when there are ~90 miles left in the trip (e.g. it was dead-on accurate for the last 160 miles), according to the GPS. I agree that it's spooky. I think, when making estimates for "miles left", our car must be doing some calculation like (rolling estimate of mpg) * (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. There's certainly a bunch of tricks they could be pulling off. The point is, from a driver's point of view, I have a trustworthy number. If they need to pull off some tricks to achieve that trustworthiness (e.g. low-balling total range), that's OK with me. With EVs, "total range" is a marketing term, so they have a strong incentives to fib about it. Unfortunately, this makes the vehicles worse to operate.

germinalphrase 3y ago
“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.
- vdqtp3 3y ago
  Most Honda models have a ridiculous reserve, something like 3.5 gallons. I still regret informing my mother of this fact...she never ran out of gas until I did.
unregistereddev 3y ago
> 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.

hot_gril 3y ago

Maybe it gives the user an underestimate then wastes gas later to meet it? :D

mrguyorama 3y ago

Fun thing about a car: They have computers that measure all those factors! Your engine knows the air density, air temperature, the rough gravity vector (used for things like hill start assist), lots of info on tire performance, speed, fuel flow, etc etc etc, with more modern cars getting things like GPS details. The estimate they use for range is based on the average fuel economy you get, not some fake model made by the EPA that doesn't represent reality. This has been true in Toyotas since at least 2004, so I would hope it could be true for a "Luxury" car from a "tech" company.

mwint 3y ago
It doesn’t measure those factors in advance.
- mrguyorama 3y ago
  It doesn't have to. It measures them in real time, and can integrate over time. Astronomers also don't see into the future but some basic calculations can let them make very accurate predictions about where the planets will be in a month. What the heck is your point?
  - mwint 3y ago
    Okay, so if I give you all the data from my car, and say it has 10.3 gallons of gas, you’re telling me you can predict how many miles it will go to within a percent? No, you can’t. Because I might go uphill or downhill. It might rain. It might be hot or cold. The car is doing something tricky (aka lying) as discussed above.
    - gen220 3y ago
      I think if you gave us a hidden buffer of 1 gallon (i.e. we actually have 11.3 gallons, but I report that you have 10.3 gallons, and selectively burn some of that buffer without reporting it), and you drive in conditions that fit within the footprint of your prior 3000 miles of driving history, yeah we probably could guess within a percent. To the best of my understanding, this is what most modern ICE cars do when they give you the "miles remaining" metric. I don't know how else they could be so outwardly accurate. This falls under the category of "trick", but it's actually a trick that helps me by allowing me to plan my trips better. Giving the "current estimate of actual miles remaining", as a multi-variate function of all the things you mention, is actually less helpful and more stress-inducing – even while it's technically providing more information, it's information that isn't very helpful.