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Old 09-25-2019, 11:41 AM   #351 (permalink)
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Quote:
Originally Posted by JSH View Post
That was more a comment on your comment the economic factors have a great impact than CAFE standards. The fact is that the average fuel economy of cars sold in the USA almost perfectly track the CAFE requirements.

The NHTSA aggressively increased mpg standards from 1978 - 1987, held them steady from 1998 to 2004, and then increased them aggressively from 2005 to 2027. Look at the graph.

We're talking past each other a bit here. I'm in total agreement that CAFE regulations have had a direct impact on improving vehicle fuel economy. My point is that overall fuel consumption, which is the top level problem being addressed, has more to do with economics than anything else. When the economy is good, a lot of fuel is consumed. When it's bad, less is consumed.

My proposal is that if reducing fossil fuels is the goal, then artificially manipulating the economics of it (taxation) is the most effective way. We might end up with vehicles as efficient as ones that exist under CAFE requirements without the overhead (waste) of running such a program, and without the incentive for officials to exchange favors for political/financial gain. Perhaps we wouldn't end up with more efficient vehicles, but instead people would just drive less. The point is, dictating the minute details of a solution to an undefined problem is not efficient.

Does CAFE even outline a target maximum fuel consumption for the state? If not, they aren't even interested in solving the problem they ostensibly exist to address. You cannot achieve a goal that is not defined.

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Old 09-25-2019, 01:22 PM   #352 (permalink)
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Originally Posted by Hersbird View Post


Its 23 now but this shows 30 mpg by 2025. And that being average not what the best are doing.
Yes, the graph shows 30 mpg but 30 = 23. Let me explain.

Your chart is from the NHTSA which administers CAFE. My chart is from EPA which is responsible for the MPG ratings on a new car window sticker. They do not use the same numbers.

NHTSA (and therefore CAFE) uses the unadjusted number from lab results. This in no way matches the fuel economy that people see when they drive their car on the street. When the EPA starting printing window stickers they use the numbers from CAFE. People complained that cars didn't get anywhere near the rated fuel economy. So EPA tweaked their numbers buy running the CAFE numbers through an equation to get a more realistic number. It was still high and people still complained. This cycle has repeated over the past 4 decades so that today the combined fuel economy on the window sticker is about 25% lower than CAFE. So a full size truck rated at 30 mpg CAFE = 22.5 mpg EPA combined.

This is crazy confusing for the average person and it isn't helped that most journalists that cover the topic don't know the difference either. It really isn't helped when people that are opposed to CAFE purposely conflate the two numbers to mislead the public buy using EPA numbers to represent current fuel economy and then the CAFE number to represent what will be required in 2025.

When I talk about fuel economy I use EPA numbers.

While I'm here I'll also touch on your topic about the EPA cracking down on diesel. This will have little effect on CAFE. The reason is that diesels don't actually help CAFE that much. While the public talks about miles per gallon the standards are in grams of CO2 per mile (or KM, or HP-Hour, etc) It isn't the volume of fuel going into the tank that matters it is the weight of the carbon coming out of the exhaust. Burning a gallon of gasoline creates 8.8 kg of CO2. Burning a gallon of diesel creates 10.1 kg of CO2. A gallon of diesel produces 15% more CO2 than a gallon of gasoline because diesel is more energy dense than gasoline. When regulatory bodies around the world started regulating g/km of CO2 they took away the advantage that diesel cars have by burning more energy dense fuel.

I hope that helps clear up the confusion.

Last edited by JSH; 09-25-2019 at 01:27 PM..
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Old 09-25-2019, 01:41 PM   #353 (permalink)
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Awesome post JSH, thanks for taking the time to articulate it so well.

This further underlies my point about the absurdity of targeting particular MPGs though. If the goal is reduced CO2, this is a roundabout way to do so. The goal isn't to burn less fuel per mile precisely, but to reduce overall fuel consumption. An aspect of this is to burn less per mile, but also traveling less miles, or chosing alternative transportation methods are other possible solutions (among many).

MPGs as a measure of efficiency is absurd in the first place, because it doesn't intuitively represent the relative fuel savings. Going from 10 MPG to 20 saves way more fuel than going from 20 MPG to 30 even though both represent an improvement of 10 MPG.
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Old 09-25-2019, 02:42 PM   #354 (permalink)
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Quote:
Originally Posted by redpoint5 View Post
MPGs as a measure of efficiency is absurd in the first place, because it doesn't intuitively represent the relative fuel savings. Going from 10 MPG to 20 saves way more fuel than going from 20 MPG to 30 even though both represent an improvement of 10 MPG.
Litres/100km is the most logic way, at least in my opinion.
Where does this miles per gallon come originally? How far you can drive with a can of petrol?
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Old 09-25-2019, 04:11 PM   #355 (permalink)
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Quote:
Litres/100km is the most logic way, at least in my opinion.
Where does this miles per gallon come originally?
It's more helpful than hogsheads per furlong?
Quote:
People complained that cars didn't get anywhere near the rated fuel economy. So EPA tweaked their numbers buy running the CAFE numbers through an equation to get a more realistic number. It was still high and people still complained. This cycle has repeated over the past 4 decades so that today the combined fuel economy on the window sticker is about 25% lower than CAFE.
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Old 09-25-2019, 04:32 PM   #356 (permalink)
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Quote:
Originally Posted by iikhod View Post
Litres/100km is the most logic way, at least in my opinion.
Where does this miles per gallon come originally? How far you can drive with a can of petrol?
Yes that is the reason. It is a very consumer friendly unit of measure for some to know how many gallons of fuel they need to buy to go on a trip. I need to go 100 miles to grandma’s house and my car gets 25 mpg so I need to buy 4 gallons. I know people that fuel their cars like this a few gallons at a time because they can’t afford to just fill the tank when it is empty.

However MPG is a really poor unit of measure to compare one car to another when you are car shopping because it is not a linear scale. For that purpose liters / 100 km or gallons / 100 miles is much more useful. Why don’t we change? The same reason we don’t use the metric system: inertia and the inability to admit the rest of the world does something better than in the USA.

FYI you can go to fueleconomy.gov and find the EPA rating fuel economy for every car sold in the USA back to the 80’s. They gave ratings for Miles per gallon and Gallons / 100 miles along with other useful things like interior volume, cost to fill a tank, estimated yearly fuel costs, etc

That is also why I use EPA numbers when talking about fuel economy standards. Anyone can go online and find the EPA rating for any vehicle sold in the USA. CAFE numbers are buried 100s of pages deep in NHTSA reports.
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Old 09-25-2019, 05:06 PM   #357 (permalink)
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My Prius has a 10 gallon fuel tank (measured at 10.2 gallons to full when completely out). It's very convenient to look at the average MPG on the display, and mentally add a zero to the end of it to get total range. If I'm getting 50 MPG, I can go 500 miles on that tank of gas. It's a very precise way to estimate range.

Regarding EPA MPG, I find that number to be quite accurate as an average people can expect. It does well to give a relative comparison between vehicles, except for those times when manufacturers cheat (EPA only tests 10% of models).
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Old 09-25-2019, 07:24 PM   #358 (permalink)
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Could one set their Scangauge to hogsheads per furling?
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Old 09-25-2019, 09:42 PM   #359 (permalink)
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An 'ogshead is ~63 gallons, a fulong 660ft or <1/10th mile. So it would be hogsheads per 100 furlong, hopefully.
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Old 09-26-2019, 01:13 AM   #360 (permalink)
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660 feet would be 1/8th of a mile.

660 x 8 = 5,280.

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