new EPA numbers vs. Old EPA numbers

I've been going back and forth on another forum about how even though the percentage reduction in the mileage estimates is greater than that of other vehicles, the amount of fuel that this change represents is actually LESS than that of other vehicles.

I'm not getting through, and could use your help!


This is the arguement I have presented so far:

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Okay, I did a little number crunching and here is a sampling. I looked at the old and new EPA numbers (combined city & highway) for a few vehicles and then calculated how much the difference translated into fuel consumption over a 1000 mile interval.

2006 Toyota Prius

Old MPG - 55 Fuel consumed in 1000 miles = 18.18 gal.
New MPG - 46 Fuel consumed in 1000 miles = 21.74 gal.
Difference = 3.56 gal.

2006 Chevrolet Malibu 6 cyl.

Old MPG - 26 Fuel consumed in 1000 miles = 38.46 gal.
New MPG - 23 Fuel consumed in 1000 miles = 43.48 gal.
Difference = 5.02 gal.

2006 Ford F-150 4WD 4.6L V8.

Old MPG - 16 Fuel consumed in 1000 miles = 62.50 gal.
New MPG - 15 Fuel consumed in 1000 miles = 66.67 gal.
Difference = 4.17 gal.

So you will see that the reduction in the EPA numbers affects all cars, and in this sample affects the Prius the least.

So the numbers weren't *fudged* on hybrids. This applies to all vehicles, and it appears to affect the larger vehicles more.

Choose a different vehicle and I will do the same analysis. I picked the Malibu as a typical mid size car and the F-150 as a typical truck.

Not to state the obvious, but the fact that the EPA numbers are changing means nothing in the real world. You will still get the same MPG you always got before. YMMV

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I followed up by using an extreme example


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I knew this would come up. Let me try to explain it better.

Let's use an extreme example. Say you had a car that got 200 mpg under the old numbers. Let's also say that the new numbers reveal that the car should only be rated for 150 mpg, or 33% worse using your math (I would call it only 25% worse myself, but that's a different argument and I won't go into that now).Now let's use the analysis on this car.

Super Efficient Car

Old MPG - 200 Fuel consumed in 1000 miles = 5 gal.
New MPG - 150 Fuel consumed in 1000 miles = 6.67 gal.
Difference = 1.67 gal.

If I had this car should I really care that the percentage difference is so great? The difference in this case is only 1.67 gallons.

This is the number that really matters where it counts...in your pocketbook.

Let's look at the difference between the old numbers and new numbers for these three vehicles and our hypothetical car in terms of dollars. I'll use an assumption of $2.50 per gallon.

Hypothetical Super Efficient Car - 1.67 gal. x $2.50/gal. = $4.18

Prius - 3.56 gal. x $3/gal = $8.90

Malibu - 5.02 gal. x $3/gal = $12.55

F-150 - 4.17 gal. x $3/gal = $10.43

This is per 1,000 miles traveled. Multiply that out over the average 12,000 miles year that is cited so much and you have the following:
Hypothetical Super Efficient Car = $50.16

Prius = $106.80

Malibu = $150.60

F-150 = $125.16

Remember that this is the difference between the old numbers and the new numbers. Which one of these decreases would cost you the most money?So why is it that you can have such a drastic percentage decrease that affects the amount of gasoline usage less than a vehicle that had a smaller percent decrease?

It's all in the fuel economy curve.


If all these numbers are giving you a headache just look at the curve. Here is a link to a rudimentary graph I created showing this curve. and my 1,000 mile example. I forgot to label it, but the Y axis is the amount of fuel used in traveling 1,000 miles. I hope it helps explain things. It's very easy to see that going from 10 mpg to 20 mpg makes a huge difference in the amount of fuel consumed, going from 20 mpg to 30 mpg is a smaller difference, and so on.

So you can see by the graph that going from 200 mpg to 150 mpg or even 100 mpg doesn't really result in that much of a difference, but any change, even small ones, along the steep part of the curve between 10 and 20 mpg can make a significant difference.

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What else can I say to get the poing across, or am I the one who is way off base here?

 

I already do feel I'm talking to a wall.

It just irks me that people say that the numbers were "fudged" on the hybrids, when in reality if affects all cars and really affects the Prius less than others, but because of the way the mpg function works it doesn't appear that way.

If we used the L/100 Km method if would be very obvious.