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What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multipleWhat is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.
clare@snyder.on.ca wrote:
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.
Vehicle position or the auto shut off point won't make any difference.
You read the amount of fuel you pumped off the pump itself.
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
clare@snyder.on.ca wrote:
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.
Vehicle position or the auto shut off point won't make any difference.
You read the amount of fuel you pumped off the pump itself. The only
real issue is odometer accuracy. That can vary with tire size variations
and factory calibration.
In article <okqbo5$c17$1@dont-email.me>, csr684@NOTyahoo.com says...
clare@snyder.on.ca wrote:
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.
Vehicle position or the auto shut off point won't make any difference.
You read the amount of fuel you pumped off the pump itself. The only
real issue is odometer accuracy. That can vary with tire size variations
and factory calibration.
If you just do it one time, you can not be sure you put in the same
ammount of fuel that was taken out.
If you keep a running total of the ammount of miles and fuel over
several tank fulls , the ammount of fuel will sort of average out.
Say you park so the back of the car is up hill and you fill the tank.
Go a number of miles and fill up again. This time the back of the car
is down hill. You may burn out 15 gallons, but only put back in 14
gallons. Ot it could be the other way around and you burn 14 gallons,
but only put back in 13 gallons. From tank to tank full there could be
a large variation. Over many tanks, the variation will average out to a
lessor error.
After say 10 tanks used you only have to contend with one or two errors
caused by the exact ammount of fuel put in the tank. Probably just the
last tank full would be where the error would come in. So instead of 1
gallon of error like the example above, you would have about .1 gallon
of error if the pumps are correct, which they should be.
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
No, steve. You are wrong. The amount of fuel you put in is the amountclare@snyder.on.ca wrote:
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.
Vehicle position or the auto shut off point won't make any difference.
You read the amount of fuel you pumped off the pump itself. The only
real issue is odometer accuracy. That can vary with tire size variations
and factory calibration.
If the first and last are identical, none of the others matter. TheIn article <okqbo5$c17$1@dont-email.me>, csr684@NOTyahoo.com says...
clare@snyder.on.ca wrote:
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.
Vehicle position or the auto shut off point won't make any difference.
You read the amount of fuel you pumped off the pump itself. The only
real issue is odometer accuracy. That can vary with tire size variations
and factory calibration.
If you just do it one time, you can not be sure you put in the same
ammount of fuel that was taken out.
If you keep a running total of the ammount of miles and fuel over
several tank fulls , the ammount of fuel will sort of average out.
Say you park so the back of the car is up hill and you fill the tank.
Go a number of miles and fill up again. This time the back of the car
is down hill. You may burn out 15 gallons, but only put back in 14
gallons. Ot it could be the other way around and you burn 14 gallons,
but only put back in 13 gallons. From tank to tank full there could be
a large variation. Over many tanks, the variation will average out to a
lessor error.
After say 10 tanks used you only have to contend with one or two errors
caused by the exact ammount of fuel put in the tank. Probably just the
last tank full would be where the error would come in. So instead of 1
gallon of error like the example above, you would have about .1 gallon
of error if the pumps are correct, which they should be.
On Thu, 20 Jul 2017 09:42:10 -0400, "Steve W." <csr684@NOTyahoo.com
wrote:
clare@snyder.on.ca wrote:
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.
Vehicle position or the auto shut off point won't make any difference.
You read the amount of fuel you pumped off the pump itself. The only
real issue is odometer accuracy. That can vary with tire size variations
and factory calibration.
No, steve. You are wrong. The amount of fuel you put in is the amount
you can squeeze into the empty portion of the tank. The amount you
used is the amount that used to be in the tank. You need to fill it to
the exact same point each time to get an accurate reading. You may
have filled your 72 liter tank to only 71 liters the last time you put
in 50 liters to fill the tank. Now, at a different station, with
different levels, you may squeeze in 73, or only 68. COSISTANCY is the
key - and where most will fall down, because, like you, they just
don't REALLY understand.
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Trip meter miles depends on circumference of driving wheels. I know my
speedo closely matches readings of roadside radar displays or my GPS, so
I guess trip meter miles will be accurate too.
Most people have a tripmeter reading and a gas pumpmeter reading.
Where they fill the tank and reset the tripmeter before driving away.
I can't find any reliable source that says what the accuracy or
repeatability of that mom-and-pop tripmeter/pumpmeter calculation, but
basic logic dictates that the errors compound such that there is likely
(IMHO) no way to get anywhere near decimal-point accuracy, and worse,
probably plus or minus 1 mpg is the closest anyone can get in terms of
repeatability and precision.
....
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger <rogermadd@yahoo.com> wrote:
What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Close to 100% accuracy if done right. I've done it on long trips. But MPG will vary
depending on terrain, weather, wind direction, stop-and-go traffic, etc.
So if you want "true" MPG for your car, you have to do it for the life of the car.
Once you do it initially, it's kind of pointless to do again except to satisfy your
curiosity.
Even the EPA's $360,000 machine only claims plus or minus 2% of the
indicared reading. I can't find where I got the notion that a mom and pop
can't possibly get closer than about 4% with a tripmeter/pumpmeter mpg
calculation - but I'm still seeking those numbers as we speak.
And, it depends on what you mean in terms of accuracy -- in terms of
absolute one needs to know the calibration error of the odometer; most
folks are satisfied to just assume it's close enough for the purpose.
If you look at simply a single fillup, it's not unreasonable to expect a
few tenths of a gallon difference between the first fillup level and the
subsequent; if you try it on shorter distances than a full tank then the
fractional error goes up.
OTOH, if one keeps track over longer periods of multiple fillups and
take some care to use the same filling pattern and only fills up after
using near the full tank capacity, then over time plus/minus targets
_will_ tend to cancel out and I have no qualms in believing a relative
performance number in the 0.1 mpg can be determined.
As noted, I've done this on long trips a number of times (generally on
first trip or so with a new vehicle, either actually new (rare) or (most
often) new to me) just to see how it compared with previous and have had
quite good comparisons on recent ones with the computer-computed
results. These would be over total distances of 1500 to 2000 miles, not
just 20 miles test runs.