More thoughts on all that Gallons Per Mile stuff, with pretty charts
click to enlarge
AutoblogGreen reader Jay S. read our recent post on gallons per mile (click the link to get caught up if you missed the discussion). He realized it's an idea he's been kicking around for a decade, and he sent in the following email, along with the charts in the gallery below:
Your Dec 16th 2008 article about a web site that lets you calculate how many gallons you use to go a certain number of miles reminded me of a chart I first made about 10 years ago. It is a plot of Gallons versus MPG for a few different total number of miles. If you look at the line for the number of miles that you drive in a year, you can see how many gallons that you will use for any particular MPG. This helps you determine what kind of car to buy.
When I first plotted this data, I was shocked that it wasn't a straight line. How could Gallons used for a given number of miles be a curve? Now, I look at it as a percentage thing. If I double my MPG, then I halve the total number of Gallons used.
Any engineer will tell you to get off the steep part of the curve, which means that you need to get at least 30 MPG, and really 40 to 80 MPG would really be doing good.
I think that this sort of study is why GM said it is more important to get better MPG in the big vehicles first, then work on the smaller ones. Making hybrid city buses was a great idea. Too bad the big SUV buyers don't really care.
Again, we don't want anyone to get the message that low MPG SUVs somehow burn less fuel than a 45 MPG Prius. It's just that when it comes to actually reducing fuel use in vehicles, there is a lot of possibility to be had at the lower end of the spectrum. Discuss. Thanks to Jay S.!
Reader Comments (Page 1 of 1)
paulwesterberg 6:37PM (12/22/2008)
More propaganda from GM. Using a 5 ton SUV to move one person around will never be an efficient use of energy.
No matter how you fiddle with the numbers you can't justify driving an SUVs to commute between home work and the mall.
Change is hard for GM and they want to keep selling the same crappy trucks that have been so profitable for them in the past.
People want affordable, efficient, clean transportation which will be coming in the form of plug in electric vehicles whether GM likes it or not.
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Derek 7:02PM (12/22/2008)
Using a 5000# (not 5 ton) vehicle to commute to work isn't GM's fault or the fault of any corporation, that is solely the drivers fault. The article even stated that this isn't trying to justify that behavior. The fact is, however, that this is the lifestyle Americans prefer and until gas prices stay permanently over $4.50 or so per gallon, that isn't going to change. The point is that since people will continue to drive this way as long as they are able, we will save more oil by improving SUV's than by improving the cars that are already efficient.
Besides, if you want to make up a conspiracy this would be Ford propoganda. Except for this past March, the F150 has been the best selling vehicle in the US for over two decades.
Mike!!ekiM 1:53PM (12/23/2008)
Derek, where've you been the last 3 years.
People has been asking for smaller engines, more gears in their transmissions and hybrids and electric cars for years.
What GM sells is a function of what GM Has For Sale. GM has lost about 20% market share over the last ten years, and GM's been Happy to drop cars and Only Sell SUV's. To slow or stop development on cars. So those sales have moved to Toyota, Subaru, Honda and the Mini.
So, why the bail out? GM has restructured the company to just sell SUV's and Trucks. Shouldn't they be allowed to die? They picked the wrong horse.
steve 7:04PM (12/22/2008)
In Europe, fuel consumption is measured in liters per 100 kilometers, which is just like gallons per mile. Is it a coincidence that their cars are much more efficient?
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Derek 7:12PM (12/22/2008)
I'm actually already a g/100m convert. I track the fuel consumption in my vehicles and looking at it this way makes far more sense because it relates directly to the efficiency of the vehicle.
Maybe if more people used this, the general public would get a better handle on consumption. Many people will look at the difference between 12 and 15mpg and say "oh, it's only 3mpg!", whereas the graph above illustrates that those 3mpg are a big change for your wallet (and oil usage too, but people care more about their wallet). OTOH, others are disappointed when going from a 28mpg to a 35mpg car just doesn't net the savings they expected.
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mark 11:23PM (12/22/2008)
In both cases it's an improvement of 25%. However, if your regular gas bill is $100/week in the SUV and $50/week in the compact, you will save $25/week with the SUV and $12.50 with the compact. But you still are paying $37.50/week more to drive the better SUV vs the better compact.
I agree showing total usage and cost per annualized mileage is much better for people who do not understand algebra very well. For someone like my parents who only drive 8000 miles/year, a 20 mpg car is fine. For me at 15K/year, a 30 mpg car is better, though they still spend far less a year than I do. 400 gallons vs 500 gallons.
Personally I don't mind the fact that SUV drivers are wasting fuel, let it run out, that will solve our oil problem. I am much more annoyed by the size and driving ability of the people behind the wheel.
Derek 8:08AM (12/23/2008)
haha, I actually just pulled those numbers out of the air, interesting that they are both a 25% improvement! Of course, taht just illustrates my point better!
Hey, here's a trick question though: If you hybridize an SUV and go from 12 to 20mpg (say you're just running your Tahoe in the city), how much does a 30mpg car have to improve to save the same amount of oil?
I, too, despise the SUV's stature more than anything else. It's like wearing a top hat to a movie theater!
mark 10:29AM (12/23/2008)
12 to 20 is 67% so 30 plus 67% is 50 mpg. You are still wasting 50/20 - 1 = 150% more oil on the SUV for the same distanced traveled though.
Derek 11:38AM (12/23/2008)
Nope, and that's the trick. Going from 12 to 20 mpg saves 3.3 g/100mi. A 30mpg car uses 3.3g/100mi. Thus, a 30mpg car must use no gas at all in order to save as much oil as one does by switching from 12 to 20 mpg. Let's face it, some people will continue to drive larger vehicles no matter what, either due to want or need. Giving these people a hybrid option has a lot of impact on overall consumption.
This is also why things like hybrid buses, delivery trucks, etc save more oil than small hybrid cars probably ever will. This is where we should really be putting our focus. Taking a bus from 4 to 5mpg effectively cancels out the oil use of a 20mpg vehicle!
Mike!!ekiM 1:59PM (12/23/2008)
No matter how you "figure it", 50 mpg beats 30 mpg, and saves you more money as well. Real Money.
Of course of your dumb enough to buy an SV as if it were a diamond ring: "Look at my big V8 engine", "My 2 ton trucks is bigger then your's", Look at my shiny diamond ring, it's got a blue tint and it's 3 carets.
If your buying a useless SUV to impress your friends, you've got other problems.
mark 2:59PM (12/23/2008)
The trick in the question is the amount of oil. I knew I would miss the trick part of it, going into my answer. You could just hook your honda up to the back of the Tahoe hybrid and go along for free.
Derek 9:47PM (12/23/2008)
True though that may be, scolding folks who drive/like trucks isn't going to save any gas. A hybrid SUV saves roughly half the difference between a regular SUV and a Prius. Being as it is unlikely to shame someone into driving a Prius (especially someone who might have very good reasons for driving a truck), I'd say that half is better than nothing.
why not the LS2LS7? 10:38PM (12/22/2008)
Can we stop crapping on the Tahoe/Escalade hybrid now?
Yes, if used wrong (to tote one person around) it's a complete waste. But hell, if I misuse a Prius I waste gas too (perhaps by driving it when I don't need to).
If you need to carry a lot of people and/or stuff, or especially towing, the Tahoe/Escalade have the potential to save a lot of gas.
Just don't buy it and then use it for supermarket runs.
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terrence_bethea 7:41PM (12/23/2008)
I still don't get the point. It's common sense that improving the efficiency of low efficiency vehicle is going to produce greater benefits than improving the efficiency of a high efficiency vehicle.
The problem with the Detroit 3 is they made little effort to improve the efficiency of ANY of their vehicles. While imports are scarcely immune, at least Nippon Inc (and Korea) produced 'some' vehicles that were closer to meeting our NEEDS rather than our WANTS.
Virtually every automaker has spent the past few decades making bigger, more powerful vehicles. GM, Ford, etc would argue that was progress b/c we have bigger, faster vehicles that use the same amount of fuel (no matter how you measure it) as they did 10 or 20 years ago. The problem is that we are using the SAME amount of fuel per distance travelled yet travelling a lot more than we did 10-20 years ago.
In essence, it doesn't matter if you call it mpg or gpm. We've made no progress EXCEPT for the people that have chosen to move from LESS efficient light trucks/big sedans/heavy coupes to smaller 4/6 bangers. Honda still doesn't make a production V8 . . . and they will likely be the sole major automaker that makes a profit for fiscal 2008 (ends March 2009).
But what's the point of talking about hybrid Tahoe/Escalades? The people that buy that vehicle class typically don't care about fuel efficiency at all so what makes anyone think they would bother to buy the hybrid version?
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!!D 8:04AM (12/23/2008)
Congrats on plotting f(x) = k/x for six values of k. Your algebra teacher would be proud.
Now, I will perform another magical transformation: f(x) = k*x^(-1)
BEHOLD! WITCHCRAFT!
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Gary 10:12AM (12/23/2008)
Nerd.
i summon you 3:30PM (12/23/2008)
I loled.
Next on Autoblog Green- EXCEL BREAKTHROUGH! Driver uses spreadsheet to predict gas savings from carpooling!
Throwback 10:47AM (12/23/2008)
steve said...
In Europe, fuel consumption is measured in liters per 100 kilometers, which is just like gallons per mile. Is it a coincidence that their cars are much more efficient?
yes it is a coincidence. The reason why European cars get better mileage is due to the ridiculously high gas prices they pay.
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Gordio 11:48AM (12/23/2008)
But avoiding to stay in the curved part is maeningless...
The curve nature of the graph is the nature of mpg's deceptiveness, and therefore staying in the flat zone is as meaningless/meaningful as staying in the curved part
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