Are MPG ratings much less accurate then they used to be?

I thought the ratings were done on a flat road on the moon where there is
1/7th the gravity in order to get those MPG results.

I never thought they were very accurate, I only use them to compare one
vehicle with another to get a relative ranking when I do a vehicle purchase.


"wraithyjeep" > wrote in message
...
> Actually MPG is determined by unused energy that is left in the emissions
> it is a chemical analysis with factors of weight and other physics that
> overall determines the MPG all this is done on a dyno. in a very
> controlled lab.
> I used to know the formula (sorry be awhile since I worked in the lab)
> the only way to truly achieve the listed MPG is with a lot of down hill
> driving.
>
>
> "General Schvantzkoph" > wrote in message
> news
>> When I bought my old Concorde in 94 the MPG ratings were pretty much spot
>> on, the car got 22 in daily driving and 29 on long highway trips which is
>> what the window sticker claimed. the MPG ratings for the new 300C is 17
>> city/25 highway which isn't even close to the real values, I'm getting
>> 15-16 in daily driving, just did a 220 mile round trip yesterday and it
>> peaked at 20 MPG. the article on hybrids (quoted in another thread) also
>> mentions that the real mileage is nowhere near the sticker values. So my
>> questions are these, has the method for determining the MPG ratings for
>> cars changed in the last 10 years? Have manufacturer's gotten better at
>> gaming the system? How do they determine the MPG ratings? It's hard to
>> see
>> how Chrysler managed to come up with a 25 MPG highway rating on the 300C
>> unless they did the test on a road that was down hill all the way.
>>
>
>

I remember way back when I used to do my own tune up, timing and all. Now I
don't even recognize what is under the hood.


"Percival P. Cassidy" > wrote in message
news
> On 07/19/05 10:25 am Richard tossed the following ingredients into the
> ever-growing pot of cybersoup:
>
>>>BTW, does the grade (or brand) of gasoline affect mpg? I sometimes use
>>>89, but mostly 87.
>
>> No, except if the motor is into serious knocking. Too much octane is a
>> waste of money and resources.
>
> the Owner's Manual for our '02 300M says 87 is acceptable, but 89 is
> preferable -- but doesn't say why.
>
> Perce

gary wrote:

> I thought the ratings were done on a flat road on the moon where there is
> 1/7th the gravity in order to get those MPG results.
>
> I never thought they were very accurate, I only use them to compare one
> vehicle with another to get a relative ranking when I do a vehicle purchase.

It depends on your driving conditions. Every vehicle I've owned in the
last 20 years has obtained within 10% of the EPA ratings. I drive a mix
of highway and city, but mostly highway (80%). I tend to get very close
to the EPA highway ratings and almost never get anywhere near the lower
city ratings.


Matt

On Sun, 24 Jul 2005, gary wrote:

> I thought the ratings were done on a flat road on the moon where there
> is 1/7th the gravity in order to get those MPG results.

The difficulty is in the stackup of assumptions and calculation margins.
The MPG protocol, believe it or don't, amounts more or less to "Let's see,
we measured *about* such-and-such percent HC and CO in the exhaust, and
the catalytic converter efficiency is *about* such-and-such percent, so we
can assume that *about* such-and-such amount of CO and HC is coming off
the manifold, which would mean that *about* such-and-such an amount of
fuel was burned".

Never mind that simply measuring the liquid volume of fuel before and
after the vehicle is run is considerably easier, more direct, more precise
and more accurate, that's not how it's done.

they are not far off problem is people do not go the 55 mph the calulations
were done at
they still use the old standard of 55mph being the national speed limit and one
i feel we need to go bac to so gas starts to stack up at the refineries and
watch how fast the price comes down

gary wrote:

> I thought the ratings were done on a flat road on the moon where there is
> 1/7th the gravity in order to get those MPG results.
>
> I never thought they were very accurate, I only use them to compare one
> vehicle with another to get a relative ranking when I do a vehicle purchase.
>
> "wraithyjeep" > wrote in message
> ...
> > Actually MPG is determined by unused energy that is left in the emissions
> > it is a chemical analysis with factors of weight and other physics that
> > overall determines the MPG all this is done on a dyno. in a very
> > controlled lab.
> > I used to know the formula (sorry be awhile since I worked in the lab)
> > the only way to truly achieve the listed MPG is with a lot of down hill
> > driving.
> >
> >
> > "General Schvantzkoph" > wrote in message
> > news
> >> When I bought my old Concorde in 94 the MPG ratings were pretty much spot
> >> on, the car got 22 in daily driving and 29 on long highway trips which is
> >> what the window sticker claimed. the MPG ratings for the new 300C is 17
> >> city/25 highway which isn't even close to the real values, I'm getting
> >> 15-16 in daily driving, just did a 220 mile round trip yesterday and it
> >> peaked at 20 MPG. the article on hybrids (quoted in another thread) also
> >> mentions that the real mileage is nowhere near the sticker values. So my
> >> questions are these, has the method for determining the MPG ratings for
> >> cars changed in the last 10 years? Have manufacturer's gotten better at
> >> gaming the system? How do they determine the MPG ratings? It's hard to
> >> see
> >> how Chrysler managed to come up with a 25 MPG highway rating on the 300C
> >> unless they did the test on a road that was down hill all the way.
> >>
> >
> >

"I can't drive ... 55"



Gary


"tim bur" > wrote in message
...
> they are not far off problem is people do not go the 55 mph the
> calulations
> were done at
> they still use the old standard of 55mph being the national speed limit
> and one
> i feel we need to go bac to so gas starts to stack up at the refineries
> and
> watch how fast the price comes down
>
> gary wrote:
>
>> I thought the ratings were done on a flat road on the moon where there is
>> 1/7th the gravity in order to get those MPG results.
>>
>> I never thought they were very accurate, I only use them to compare one
>> vehicle with another to get a relative ranking when I do a vehicle
>> purchase.
>>
>> "wraithyjeep" > wrote in message
>> ...
>> > Actually MPG is determined by unused energy that is left in the
>> > emissions
>> > it is a chemical analysis with factors of weight and other physics that
>> > overall determines the MPG all this is done on a dyno. in a very
>> > controlled lab.
>> > I used to know the formula (sorry be awhile since I worked in the lab)
>> > the only way to truly achieve the listed MPG is with a lot of down hill
>> > driving.
>> >
>> >
>> > "General Schvantzkoph" > wrote in message
>> > news >> >> When I bought my old Concorde in 94 the MPG ratings were pretty much
>> >> spot
>> >> on, the car got 22 in daily driving and 29 on long highway trips which
>> >> is
>> >> what the window sticker claimed. the MPG ratings for the new 300C is
>> >> 17
>> >> city/25 highway which isn't even close to the real values, I'm getting
>> >> 15-16 in daily driving, just did a 220 mile round trip yesterday and
>> >> it
>> >> peaked at 20 MPG. the article on hybrids (quoted in another thread)
>> >> also
>> >> mentions that the real mileage is nowhere near the sticker values. So
>> >> my
>> >> questions are these, has the method for determining the MPG ratings
>> >> for
>> >> cars changed in the last 10 years? Have manufacturer's gotten better
>> >> at
>> >> gaming the system? How do they determine the MPG ratings? It's hard to
>> >> see
>> >> how Chrysler managed to come up with a 25 MPG highway rating on the
>> >> 300C
>> >> unless they did the test on a road that was down hill all the way.
>> >>
>> >
>> >
>