In many ways the US is a very backward place. Certainly our population on average shows poor math and language skills.

Fair point, although I still think that it is prone to abuse.

For those who prioritize fuel economy, the formula is straightforward — drive the most fuel efficient vehicle possible. If the goal is to save money, rather than fuel per se, then do a cost-benefit analysis to see whether paying for a more efficient vehicle is worth whatever increase in expense may come from the change over.

To the extent that a larger vehicle is needed, use the larger vehicle as little and as efficiently as possible, and to defer to using the more efficient vehicle or another alternative as much as you can.

(In the previous post, I meant to refer to the Cobalt, not the Corolla, so sorry for any misunderstanding.)

The auto manufacturers went ballistic. They had a vested in an obscure fuel consumption convention; one that muddied information, maximized confusion and inspired disinterest. They successfully lobbied for the convention to be changed to liters per 100 kilometers.

It exceeded their expectations! So few understand metric people stopped thinking and talking about mileage. I doubt one in 100,000 knows his car’s fuel consumption.

Do you trade the old Accord for a Prius, or do you trade in the Tahoe for a CUV? Answer: just eyeballing the MPG figures can be misleading, and you’re better off doing the math — calculating the gallons used per 10,000 miles driven in each choice, to see if trading in the sedan or people mover would save the most gas.

You’re close, thanks for going through that.

The subtext to all this is that I see a study like this as being fodder for gross misinterpretation and abuse, particularly by the supporters of gas guzzlers who will surely post this story all over the internet as “proof” that getting 20 mpg is better than getting 40 mpg.

Based upon other news accounts, the point of their study was that gas guzzlers from the road are the low hanging fruit in any program to lowering gas consumption. Their work, at least as far as I can tell, was not intended to encourage crossover sales.

Absolutes still count for more than marginals, because they get to the bottom line and force a view of the big picture. It’s that same abuse of marginal analysis that makes a Civic a better car than a Corolla. Honda benchmarked the absolute (reviewed the entire market, took the best of the market, and benchmarked them in order to beat them), while GM benchmarked itself (looked at its own last effort, then added a few percentage points of improvement.) When the focus is on the marginal, the tendency is to not do much.

It’s a clear way to compare any set of vehicles at a given moment. This CPM would vary from week to week as fuel prices change, of course, but this would affect all cars equally.

It’s much more difficult to predict payoff points for fuel-saving improvements. As fuel prices rise, so does the value of every gallon saved.

If you assume that Tahoe drivers will just continue to drive Tahoe-sized vehicles, and Corolla drivers will just continue to drive Corolla-sized vehicles, then yes, starting a hybridization program with the biggest gas hogs is the most efficient way to go — also assuming that the per-car cost of hybridization does not vary much based on the size of the vehicle. So yes, under those circumstances, GM made the logical choice.

But there are two assumptions there, and it seems as if both turn out to be untrue in the real world. As for the first, plenty of Tahoe drivers don’t seem to value their Tahoes all that much, as people are shifting in droves to smaller cars due to additional fuel costs of around ~$2000 per year (or less) compared to two years ago. So the question becomes, why bother hybridizing Tahoes, when an even easier solution is to scare three quarters of your Tahoe drivers into buying smaller cars? This is what Pch101 seems to be getting at in his posts, and what Europe has been doing for years with high gas taxes.

The second assumption, that the hybrid premium for large vehicles is not much different than the hybrid premium for small vehicles, also seems to be untrue. This is just based on a casual comparison of MSRP differences between cars like hybrid/regular Civics, Prius vs. optioned-out Corollas and Camrys, regular vs. hybrid Tahoes, etc., accounting for various option packages.

Given all that, it’s not hard to understand what’s been going on. The gas-hog drivers who felt they had a choice are now fleeing the gas-hogs, mostly for ordinary, non-hybrid compact or midsize cars. The seriously green crowd has been piling onto the super-efficiency bandwagon, as a fashion statement as much as anything else. The “sensible shoes” crowd that actually cares to live modestly or frugally still buys used Corollas and drives them into the dust, 150,000 more miles down the line, and has barely missed a beat. Political candidates who need to drive green and drive domestic at the same time will buy Escape hybrids. Eventually, the few Tahoe-drivers who actually still value the utility of such a vehicle will inquire into hybrid options, and buy that option only if it saves more than it costs.

So yeah if you’re trying to figure which of your cars to sell to get higher efficiency, keep gpm in mind, but I bet which one is older or needs repairs, life style changes or equity in the vehicle all take priority.

MPG just seems like an easier way of comparing the efficiency of vehicles. Even though, either way will work. Using a figure like 100 km always seem just like some arbitrary number to me … oh wait …. gallon is an arbitrary number too …. Fooey,… I still prefer mpg.

Frankly, I would rather just switch to the metric system, get it over with, and avoid the whole discussion.

You could switch your units of gas over from gallons to metric quite easily. A liter is 1.0566 US quarts, so you could call it the metric-quart. And 4 metric-quarts could = 1 metric-gallon.

A metric-gallon (MG) would be 5.6% bigger than your current gallon … MPMG…!!!

Actually, that is the point.

What should happen in this scenario is that Driver B should assess the big picture, develop a holistic goal and figure out how to meet that. That may mean punting on the Tahoe and the Traverse entirely, or finding a way to fundamentally change his manner or level of consumption so that he uses less of either.

When abused, marginal analysis tends to be destructive because it actively encourages small picture, short-term thinking just like this. It’s that very mentality that allows someone to say that 40 is less than 20 with a straight face.

Mathematically, I understand the point being made and the authors are accurate in the details, but in the big picture, the analysis falls flat because it fails to look at the aggregate.

It’s a bit like the allegory of the blind man and the elephant — these guys have stumbled upon the trunk, and they’re now telling you how to extract more water out of the hose that they’ve just found. By missing the big picture, the wrong little picture gets drawn.

By doing this, you can round to two significant digits, similar to that of typical mpg figures. 1000 miles is also close to the average number of miles a car is driven in a month, which makes monthly budgeting a bit easier.

The level of discussion (with some exceptions) on this site is far and away the most rational and enlightened of any commentary site I visit , BY FAR! What a pleasure.

Intersting to think othat my recent careful driving of my corolla results in its burning 2.24 gallons per 100 miles.

Here is another good write up of this concept.
http://www.caranddriver.com/features/columns/c_d_staff/patrick_bedard/mileage_no_it_s_your_gallonage_that_really_counts_column

Hooray!!! Someone got it right!!!

The Law of Diminishing Marginal Returns dictates that you will choose that which improves your utility the most first, then on to the next, the the next until you reach a point where there is either no improvement or an actual worsening.

In this instance it means the Tahoe -> Traverse trade is the most economically rational choice of the given options.

There are two problems we are now facing, and will be dealing with more and more in the future.
(1) Multiple energy source vehicles.
(2) Fair road use taxes.

Multiple energy source vehicles:
Automobiles are going away from a single energy source (gasoline) model. There are now, and will be even more, multiple energy sources.

Using distance/gallon or gallons/distance doesn’t matter anymore because it is only measuring one energy source. If you have a plug-in hybrid, how do you compute the mileage?

A new inclusive system needs to be used. Cars need to be measured as distance traveled for a given unit of energy, lets say a kilowatt. That measure needs to be an average of the energy fed from OUTSIDE the vehicle. Thus, energy recapture systems won’t skew the average.

That kilowatt can be derived from gasoline, diesel, fast food grease, ethanol, natural gas, electricity, compressed air, or other sources of energy.

The mix of fuel sources varies. But for the most part, a car will have at most 2, perhaps 3, sources of energy. The mix ratio can be measured based on averages from city or highway driving.

So the buyer can have the kilowatts by energy source for two driving conditions. But at the end of the day, what people want is a rough guess of how much a vehicle will cost to operate. So how do you covert these numbers to something that is not impacted by the price of an energy source?

You can’t. In the old days it was easy. There was only one variable because there was only one fuel source. However, it doesn’t have to be that bad. With the Internet almost everywhere, and small computers everywhere (cell phones for example), a buyer could enter the base kilowatt numbers into a website or application and ask it to derive a cost based on fuel prices that day.

An online operational expense calculator can be run by a government website. In fact, a good web site can have all the ratios and fuel types on file. Just enter a make/model and let it look up the ugly details and do the math. Then you can compare car A to car B and now how much it will costs you to operate them.

Fair Road Use Tax:
The idea of MPG also directly relates to how road uses taxes are assessed. The current system, collect at the fuel pump, is becoming more and more unfair. What if your car gets 50 percent of it’s operational Kw from your home electrical outlet? That electricity is not taxed with road use taxes.

It is also unfair that one car of equal road wear-n-tear uses half the taxed gasoline of another car.

The bottom line is that cars will need to be taxed annually (or so) based on a sum of actual energy used plus miles driven. The energy consumed by the motor can be tracked, no matter what source of energy the motor draws on. The miles are tracked via odometer, as normal.

By collecting these two variables, a fair tax can be computed. This way, two cars of equal road wear-n-tear will pay the same. Cars that carry more weight, or drive more, will pay their fair share of road use taxes.

By thinking about cars in terms in kilowatts instead of gallons, we can solve a lot of complicated problems that we will be facing in the future.

Bunter

But the supposed point of the article is pretty pointless. When does anyone in the real world need to analyze whether switching from a Tahoe to Traverse will save more gallons than switching from a Corolla to a Prius?

Never, that’s when. You’re either looking to trade in your Tahoe or you’re looking to trade in your Corolla. No surprise people haven’t developed intuition about a tricky arithmetic problem they NEVER face in real life.

If you’re some economist or analyst doing a research study, then you are probably analytical enough to think through the problem. No one else would need to bother.

If you’re looking to improve fuel economy and you live in a MPG regime like we do, you pick the car with the highest MPG. Period. End of story. That’s simple. Nothin’ wrong with that.

Haven’t time to run the numbers but it might just save more fuel then the ‘Hoe vs. Traverse.

Not saying that most ‘Hoe drivers won’t be better served by the Traverse, they will.
Shoot most will do even better with the “horrors” Minivan (improvement_needed, dead on).

Worth a thought.

Chuckles.

Bunter

2) car makers already put an ‘estimated fuel cost / year’ on their window stickers… – this scales the same as g/100miles…

3) if you really want people to consider things, you should calculate your TRUE cost to own… (ala – edmunds)… – imagine if that was put on window stickers???
from edmunds (base models)
tahoe: 78 cents/mile
oddesy: 56 cents/mile
enclave: 75 cents/mile
sienna: 59 cents/mile
caravan: 56 cents/mile

all automatics
civic (EX): 46 cents/mile
civic hybrid: 46 cents/mile
corolla (XLE):52 cents/mile
prius (base): 54 cents/mile

unfortunately, when doing this, i calculated that it costs me ~ 50 cents/mile to drive my current vehicle – thus – when making a trip, the question needs to be asked: do i need to drive 60 miles to go somewhere? – that trip will cost me 60$… (round trip)…
of course, by owning a vehicle, your sunk costs are typically much greater than your variable costs…

edit: who would buy a chevy traverse????
much better off in a minivan – ridiculously cheaper to own / operate

It’s obvious that if Driver A trades a Corolla for a Prius, and Driver B trades a Tahoe for a Traverse, then Driver A is absolutely better off because he has the lowest absolute fuel bill. That’s not the point.

Suppose Driver C owns both a Corolla and a Tahoe, and he only has enough money to trade one vehicle. In which case is he better off? Using the egghead analysis, we can see that he’s better off trading the Tahoe for a Traverse and keeping the Corolla, since that is the path to the absolute lowest fuel consumption. This, I believe, is the point of the study. Most ‘men on the street’ would tend to put their money towards the sexy, uber-mileage Prius thinking they were getting the best answer . . . but would be wrong.

(And please no one pipe up with any ‘trade em both for a Prius’ suggestions, since that simply evades the question . . . some people need Tahoes/Traverses, and some need Corollas/Priuses.)

Extend this logic to the US vehicle fleet in aggregate. If we have limited resources to apply towards improving FE, then this study shows that we can get the most bang for the buck by spending it on improving the worst offenders. Thus, the marginal analysis at the individual level — along with the reality of limited resources — produces the best absolute answer in aggregate.

I believe this concept is also known as the ‘law of diminishing returns’.

Now, combine this with the fact that it is usually easier to find ways to improve the gross offenders than it is to squeeze more performance out of your already best-in-class. Together these make a very compelling case for the GM strategy of focusing FE efforts on the gashogs.

However, this is not the politically correct answer (and not coming from the political darling), so it is easy to slag on it. This reminds me very much of the battle to reduce non-CO2 tailpipe emissions (boy, the good old days) . . . California found it easy to mandate ever lower and lower limits for new cars that were harder and more expensive to meet, all while neglecting the fact that removing a few thousand blue-smoke-spewing hoopties would have a greater overall impact on crud flung into the air. However, blue-smoke-spewers tend to be owned by the poor and underpriviledged, and it’s not politically correct to force them to give up their transportation. Hence, the PC but suboptimal solution.

Another note . . . I think it’s a bit funny to see the back-patting here, saying that the commenters at TTAC have known this all along. I don’t think so. I’ve seen plenty of discussions about CAFE here, and the CAFE calculation deals with basically the same issue (the ‘average’ in the name is a geometric mean, not the normally understood arithmetic mean). The majority of the commentors do not understand a calculation as simple as figuring the ‘CAFE’ of two individual vehicles. I don’t think this was any more obvious to the readers here than the general public . . .