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

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.

AC is off during tests. That is why hybrids results are ridiculous. As for
the Hemi, perhaps it was optimized to turn off extra cylinders during the
test and your driving habits do not mirror those test circumstances.


"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.
>

On Mon, 18 Jul 2005 14:02:45 +0000, Art wrote:

> AC is off during tests. That is why hybrids results are ridiculous. As for
> the Hemi, perhaps it was optimized to turn off extra cylinders during the
> test and your driving habits do not mirror those test circumstances.

Hard to believe that AC makes a 25% difference in a 4000lb car. The flat
surface for the government tests could be the reason for the huge
difference. 300Cs are very heavy and New England (where I live) is very
hilly even on highways. Lugging a 300C up a hill probably puts enough
strain on the system that all 8 cylinders are engaged which means that you
are going to use much more energy going up a hill then you get back going
down the other side because the engine is operating in it's less efficient
mode on the upside of the hill. I wonder how hybrids behave on hills. On
the one hand a true hybrid like the Toyotas will have to engage it's
gas engine more on the other hand they recover more energy on the down
side of hills because of the regenerative breaking.

In the hybrid, as soon as AC goes on, gas engine goes on. That is why EPA
test results are a joke.


"General Schvantzkoph" > wrote in message
news
> On Mon, 18 Jul 2005 14:02:45 +0000, Art wrote:
>
>> AC is off during tests. That is why hybrids results are ridiculous. As
>> for
>> the Hemi, perhaps it was optimized to turn off extra cylinders during the
>> test and your driving habits do not mirror those test circumstances.
>
> Hard to believe that AC makes a 25% difference in a 4000lb car. The flat
> surface for the government tests could be the reason for the huge
> difference. 300Cs are very heavy and New England (where I live) is very
> hilly even on highways. Lugging a 300C up a hill probably puts enough
> strain on the system that all 8 cylinders are engaged which means that you
> are going to use much more energy going up a hill then you get back going
> down the other side because the engine is operating in it's less efficient
> mode on the upside of the hill. I wonder how hybrids behave on hills. On
> the one hand a true hybrid like the Toyotas will have to engage it's
> gas engine more on the other hand they recover more energy on the down
> side of hills because of the regenerative breaking.

"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.

The government determines the fuel consumption ratings not the Manufacturer.
The tests are conducted on a flat surface without using air conditioning,
and using average temperatures 70 - 80 degrees. And does not factor in,
stop and go driving ,or different road grades.

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 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.
>>
>
>

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.
> >>
> >
> >