Gallons/100 Miles (now provided by EPA)

The emphasis is different and skewed especially in this day and age. Under the MPG system there is no responsibility for use of fuel....it's a game. 'My car's better than your car in fuel economy it can go farther.' That mistaken emphasis is all over the advertising we hear every day.

The GPC system more accurately assigns responsibility for usage of fuel in that it correctly calculates how much fuel is used for a given fixed distance.

In addition mathematically using MPG to come to an arithmetic mean or total in quantity is erroneous. Adding two or more rates then dividing to get an average is incorrect.

Two vehicles one getting 50 mpg and the other getting 20 mpg each driven the same distance ( 100 miles ) do not actually consume fuel at the 'apparent' average of the two; i.e. 35 mpg or 2.86 GPC.

Actually the first vehicle uses 2.0 gal to go 100 mi while the second uses 5.0 gal to go 100 mi. Now those two numbers can be added and averaged to come to a 3.75 GPC 'true' average.

This is the lie of the US ( and import ) auto industry here in the US. "We have a truck that gets 18.0 mpg on average and an auto that gets 40 mpg on average so our two vehicles together get 29 MPG!" Great HUH?

One is lead to believe that if the two different vehicles were each driven 100 miles that together they'd use 6.9 gal of fuel ( 200 / 29 ).

In actuality the two vehicles use 5.6 gal and 2.5 gal respectively, or 8.1 gal together.

That's a slight error of 18%!!! The US automkers don't want to change from the comfortable and well-known MPG system.

 

Thanks for the explanation. I didn't realize how the 'fleet' average was derived by and that is where the issue is, not how, me, the consumer sees that tag on the car window. To me personally, for that car, both tells me the same thing, consumption either way.

 

I'd rather go 100 miles per gallon than 1 gallon per 100 miles. Isn't 100 better than 1? (Lol!).

 

So the 2010 Prius should get 2 Gallons / 100 Miles.

 

It would be nice if they'd give us gas just for driving it!

The 2010 will USE gasoline at an estimated rate of 2 gallons per 100 miles. (Yes, I know that's what you meant, but it just seemed like a good time to make the little point. No additional offense intended.)

 

Ok, point taken.

I was thinking along the EPA rating. That's why I used "should" instead of "will" because the official numbers are not yet released.

 

Versus his *regular* amount of offense, I guess.

Uh... but even so. It "should" use 2 gallons per 100 miles... intead of GET 2 gallons per 100 miles.

That was the offensive point being made. Not the difference between will and should. The difference between get and use.

Great discussion guys.

 

Our CAFE standards are figured this way, from what I understand. Using this "wrong" math. And that's a travesty.

 

I've never researched these regulations to find out how this determination is made. Certainly, the math is "correct" if you are supposed to determine the "average" MPGs by computing a simple mean. As has been pointed out, however, such "correct" math hides the real use of gasoline. Do you have any references regarding these calculations, conducted per the regulations?

Hey! Remember, Darell: Don't ask; don't tell.

Hmmm. Sarcasm?

 

*regular* or additional, I did not sense any offense from him because he is a very nice guy in person when we met in Detroit.

I think you missed my point too. The discussion prior to my post was on the usage but I was replying to the topic (EPA rating).

I was simply saying what label / rating the 2010 Prius will get from the EPA once it has gone through the official testing procedure.

Well, maybe I am missing something here. If that's the case, I don't mean to add another extra offense on top of the "additional".

 

Is additional offense like a flagrant foul in the NBA? :madgrin:

 

I like gallons / 100 miles and Liters / 100 kilometers as a measurement of fuel consumption. However, I think switching to a measurement based on consumption would be counter-productive if the goal is to get people to buy vehicles that consume less fuel. The reason is in the "wow" factor.

Take these 3 Honda's

2009 Fit ----------------- 31 mpg
2009 Civic Hybrid ------ 42 mpg
2005 Insight 5M -------- 52 mpg

The public says "wow, the civic hybrid gets 11 more mpg! and the Insight gets an amazing 21 more mpg!"

Now look at these same 3 Honda's:

2009 Fit ----------------- 3.2 g/100 miles
2009 Civic Hybrid ------ 2.4 g/100 miles
2005 Insight 5M -------- 1.9 g/100 miles

Now the public says "That Insight ONLY uses a half gallon less fuel in 100 miles?"

I just don't see the public getting excited about differences that will be measured in 1/10ths of a gallon.

50 MPG = 2.0 g/100 miles
60 MPG = 1.7 g/100 miles
70 MPG = 1.4 g/100 miles
80 MPG = 1.2 g/100 miles
90 MPG = 1.1 g/100 miles
100 MPG = 1.0 g/100 miles
110 MPG = 0.9 g/100 miles
120 MPG = 0.8 g/100 miles
130 MPG = 0.8 g/100 miles
140 MPG = 0.7 g/100 miles
150 MPG = 0.7 g/100 miles

As you can see a consistent increase of 10 MPG becomes a smaller and smaller reduction in a consumption based system like gallons per 100 miles.

 

I find the whole quantity per distance verses distance per quantity issue silly. This debate is just more proof that our educational system does a poor job teaching basic math concepts. Even a high school math student should be able to instantly recognize that the two methods are functionally equivalent. One is simply the inverse of the other, like ohms and mhos in electronics.

Before anyone feels the need to enlighten me on why one or the other is better for emphasizing one view or the other, let me save you the effort by saying I completely understand. I simply think it's silly that people can't see the underlying data either way.

Tom

 

The legal US measuring system is SI, the modern "metric" system. We have metric money, cars, movies, computers, skis, guns, medicine, soft drinks, wine, liquor, paper and a whole host of other items in daily life. SI was established as the preferred system of measurement by the Acts of 1866, 1975 (Ford), the Omnibus Trade and Competitiveness Act of 1988 (Bush) and subsequent presidential orders. Costco sells milk in three Liter containers. All exports to Europe must be exclusively in SI units effective 2010. Now, we just need the EPA and other agencies to conform to federal law. Glad we are finally making a transition to fuel per 100 kilometers. Now if the Prius could just toggle between °F and °C, we will all remember that "a gram of prevention is worth three kilograms of cure."

 

While talking about metric units, don't forget the millihelen. That's a unit of facial beauty sufficient to launch one ship.

Tom

 

True enough, but when measuring the change or even rate of change, what have you determined is the appropriate metric unit in time? Is epoch metric? How about æon (seems more appropriate for the "time" frame)?

I think we'd probably just default to the good old American unit of Blue Moon.

 

I think that for the sake of a future conversion to the Metric system, the US should use a temporary hybrid measurement such as "miles per Litre" or "gallons per 100 kilometers". That would allow the Americans to gradually get used to the Metric system.

Just like the tires....
P195/55R16.... 195 is the width in millimeters, 16 is the rim diameter in inches.

/sarcasm

 

What this country needs is more miles per gallon from every vehicle that is sold, not another measurement system. It's great that the 2010 Prius will break the 50 MPG mark for fuel economy. Sorry, but the sub 2 gallon per 100 miles does not excite me.

 

in reply to both.. it's the D3 advertising that implies and thus misleads the unknowing public. Actually for CAFE the NHTSA does the math correctly and converts all vehicles to a usage basis. They even have a good explanation on their website as to why and how they do it.

The NHTSA as part of DOT monitors CAFE. The EPA has no say in it. But......the NHTSA still uses tests that are nearly 30 years out of date. When they say that the vehicles have to average 35 mpg by 2020 that is NOT the new EPA numbers on the window stickers.

In fact to meet the 2020 standards the vehicles only have to have an equivalent EPA rating of about 28.5 mpg on average. An awful lot of vehicles already meet that criterium.