Plx Kiwi Gives Feedback to Help Save on Gas

Driving habits are a very major influence on how much gas we use. If you want to improve your fuel burn, it is a big help to be able to see the rate of fuel use in real time. Real time feedback is a great way to learn. The Scangauge is one device which can give you this feedback. The Plx Kiwi, featured in the video, is another.

Keeping An Eye on the Gas Price

The US Energy Information Administration publishes data on average retail gasoline prices. This lets us keep an eye on the general condition of the country's gasoline economy. As you can see from the chart, gasoline has been gradually getting expensive over the last while. We are now are a national average just above $2.80. That is still far below the spike of summer 2008. However, it is all too easy to fall into the "boiling frog trap" ... the phenomenon where slow changes are ignored until it is too late. The gradual upward trend in the gas price is a sign that we had better prepare for expensive gasoline in the future, even if right now it is not so bad.

Tests Prove It : Tonneau Covers Help Trucks Save Gas

Pickup trucks can gain a significant aerodynamic improvement if they are fitted with a tonneau cover. That can lead to as much as a 10% reduction in fuel use. They say seeing is believing, and this video shows a road test which reveals the advantages of fitting out your truck with a cover.

Special Tank to Ease Measurement

To know whether you are saving on gas and how your different driving techniques and vehicle mods are working out, you have to accurately measure how much gas you are using. To detect small changes at the percent or so level you have to put in quite a bit of effort to be able to clearly measure it. This video shows an extreme: the installation of a new gas tank that makes measuring more accurate.

What We Measure Is Important

What we measure is important. It shows the things we are preoccupied with as a society and it enables individual action. We don't measure that which we consider unimportant. It is impossible to act consistently if you have no feedback on what you are doing. The fact that our cars all have odometers for measuring distance traveled and speedometers for showing how fast we are going but no instrument to show the instantaneous gas mileage (ie gallons per hundred miles or GPHM) shows how little Americans think about fuel. Gasoline is considered to be something which will always be so cheap and available that it is not worth measuring. The lack of such an instrument makes it hard to adjust your driving habits to improve fuel economy. However, throughout the world attitudes are starting to change. For example, in Britain all homes are going to be fitted with new electricity meters that show the instantaneous consumption, so that homeowners can see the energy cost of turning on an appliance or activating the air conditioning. You can upgrade the instrument panel of your car to show you instant fuel usage by installing something like the scangauge. I believe that all cars should be required to include in their instrumentation a meter showing instantaneous fuel economy. That would both make us think about saving on gas and make it a lot easier to learn how to do it.

Do You Know How Many Miles You Drive?

The Center for Transportation Analysis of the Oak Ridge National Laboratory has a publication called the Transportation Energy Data Book. In it you can find all sorts of interesting data. There is a section called Self-Reported vs.Odometer Average Annual Miles available as a Microsoft Excel spreadsheet. One fundamental principle of saving on gas is that you have to know how much you are using to know if you are saving or not. You have to know how much gas you are putting in your tank how often and how many miles you are driving in between fills. Getting into the habit of watching these things is important. Otherwise it is all too easy to forget everything except for the last fill up. That can convince you of things that are not true.

For example, maybe you tried a new hypermiling technique for a couple of days. Then you went to the pump and were surprised at how much money the bill was. You conclude the technique did't work. But what you might not be aware of is that you actually drove quite a few more miles before that fill. Or maybe traffic was especially bad. You have to keep a long term watch over what is going on.

Anyway, the interesting thing about the self reporting odometer study done by Oak Ridge is that on average people do not know how far they drive in a year. I have reproduced the data from the study here.

Self-Reported vs. Odometer Average Annual Miles, 1995 NPTS and 2001 NHTS

Vehicle age (years)	1995 self-reported	1995 odometer	2001 self-reported	2001 odometer
Under 1	15,900	15,600	15,500	14,500
1	16,800	14,500	14,300	14,200
2	15,500	14,800	14,000	13,700
3	14,400	13,800	13,100	14,100
4	14,100	12,900	12,500	13,400
5	13,500	12,700	12,000	12,900
6	13,200	12,400	11,800	12,400
7	12,800	11,600	11,600	12,100
8	12,200	11,300	10,900	11,300
9	12,200	11,200	10,800	10,500
10 and older	8,900	9,000	7,400	8,100
All household vehicles	12,200	11,800	11,000	11,800

The study was done twice, once in 1995 and again in 2001. Both times Americans said they traveled an annual distance that the odometer disagreed with. One observation is that in the years between the studies, the error switched sides. In 1995 Americans thought they drove more than they actually had. This conservative estimate would help to reduce gas usage and let families build a little safety into their financial planning. But in 2001 Americans thought they had driven less than they really did. This is a worrying trend. Underestimating your driving is likely to discourage efforts to save on gas. It also throws off family budgeting because it will generate unexpected shortfalls. Kind of like the "all risk" style of modern banking.

National Fuel Gauge Reading Full

The Energy Information Administration keeps track of the total amount of gasoline in storage in the United States. This information is of interest because historically when the amount is low, the price of gasoline rises. This can happen regardless of the price of oil, the bottom of the pyramid in the gasoline production chain. Short term gas prices are set by the relation between demand for gasoline and the supply available. The EIA publishes a report called the Weekly Petroleum Status Report where you can always find the latest updated information.

In the graph, taken from the current Weekly Petroleum Status Report you can see how in September 2008 the amount of gasoline was well below the gray average band. We also had record fuel prices in that time. Right now the national gasoline supply is above average. Good news for drivers! Keeping an eye on this graph is like keeping an eye on the nation's fuel gauge. When it starts dropping below the average range, watch out for high gas prices!

Monitor Your Gas Mileage

Driving habits are among the biggest contributors to saving on gas. But it is difficult to improve your driving without knowing how you are doing. Instantaneous feedback lets you know if a particular tip or trick actually works for example. The scangauge II is a little computer than plugs into the standardized diagnostics port under your dash. It reports the instantaneous and average gas mileage. Unfortunately it reports in MPG, not in GPHM which would be better. The video has an interview with an executive from the company that makes the ScanGauge II. Like he says, with this device saving gas while you drive becomes like a video game.

How Can GPHM (Gallons Per Hundred Miles) Help?

Using MPG (Miles Per Gallon) to measure the fuel economy of a vehicle can lead to some wrong impressions. It is not that there is anything wrong with MPG itself, just that it measures something that we don't normally use. Much better is to think about fuel economy in GPHM (Gallons Per Hundred Miles). Here is an example that shows how easy it is to be confused with MPG.

Assume you have a car that gets 10 MPG in the city and 20 MPG on the highway. Now this car goes on a trip that is 10 miles in the city and 10 miles in the highway. Over this 20 mile trip, what is the average MPG that you got? If you said 15 MPG you are mistaken. It looks like it should be 15 because 15 is the average of 10 and 20. But unfortunately MPG does not work that way. Let us see why not.

Over the first 10 miles in the city your car used 1 gallon of gas because it went 10 miles and gets 10 miles per gallon. Over the next 10 miles on the highway, you car used 0.5 or one half gallon of gas because it went 10 miles and gets 20 miles per gallon. This means your car used 1 gallon plus one half gallon or 1.5 gallons for the whole trip. The total mileage of the trip was 20 miles. This means the MPG for the trip was 20 miles per 1.5 gallons or 13.3 MPG! Not 15 MPG.

What happens if we use Gallons Per Hundred Miles or GPHM instead? To convert MPG to GPHM divide 100 by the MPG rating. The car gets 10.0 GPHM in the city and 5.00 GPHM on the highway. If we average 10 GPHM and 5 GPHM we get 7.50 GPHM. Is that the right answer? If we convert the 13.3 MPG we found before, it comes out to be 7.50 GPHM on the nose.

So you can average out GPHM ratings and you can't average out MPG ratings. This is a perfect example of why we would be better off using Gallons Per Hundred Miles (GPHM) and not MPG when we talk about fuel economy. GPHM works out like we expect, but MPG can be tricky and you can easily fool yourself.

Why does this happen? Well, it is because the two measures are thinking about taking different things as givens or fixed. With miles per gallon (MPG) you are thinking about using a fixed amount of gas and seeing how far you can go. The idea is to talk about the range you can get with a given amount of gallons.

With gallons per hundred miles (GPHM) you are talking about going a fixed distance and seeing how much gas it will use up doing it. Here you are talking about the fuel usage that it will take you to cover a fixed distance.

Now we can see the root of the problem when we try to use MPG for fuel economy. MPG assumes that you are going to use a fixed amount of gas and tells you about the different ranges different cars could get. But assuming you will use a fixed amount of gas is wrong. We want to go a certain distance. We don't say "I will drive until my car uses up 10 gallons." We say "I will drive to work (which is a distance of 10 miles away)." We should use GPHM to talk about fuel economy because the whole point of saving on gas is not to use a fixed amount of gas, but to change the amount and make it lower.

If you want to read more about this, I wrote about it before and the experts explain it really well here. As always, Wikipedia has useful information. And here is a handy calculator you can use to make conversions.

Gallons per Hundred Miles or GPHM

Have a look at this New York Times Year in Ideas article, which talks about a new and better way to measure the fuel economy of our vehicles. They suggest we use gallons of gas used to go a hundred miles instead of the traditional miles per gallon. The old way (MPG) tells us how far we can go on a certain amount of gas. The new way (GPHM) tells us how much gas we use to go a certain distance. So why the change? What is wrong with the old way?

Well, there is nothing wrong with it, but it can be very misleading. Basically the old system (MPG) is set up for calculating the range of a vehicle given the amount of gas available. You multiply the amount of gas you have by the MPG number to get the miles you can go. But in the world of fuel economy, we want to ask the opposite question. We want to know how much gas a vehicle will use to go a known distance. Using MPG as a fuel economy rating can give surprising results.

For example, consider a family (call them the Jones') that has a Ford F150 pickup truck that gets 10 miles per gallon. Their neighbors (the Smiths) have a Prius that gets 40 miles per gallon. We pretend that the two families drive these vehicles exactly 10 000 miles in the year 2008. How much gas did each family use up? The Jones' burned through 1000 gallons of gas while the Smiths used 250 gallons.

Okay, now imagine that each family tries to improve the gas mileage of their vehicle. They maintain the tire pressure at the correct value, replace the air filters and have a four-wheel alignment done. As a result, they each enjoy a 3 MPG increase in mileage. Now the Jones' get 13 MPG with their F150, and the Smiths get 43 MPG. In 2009 they again each put 10 000 more miles on their vehicles. How much gas did they burn up in 2009? The Jones family used 769 gallons while the Smith family used 233 gallons. Year over year, the Jones family saved 231 gallons but the Smith family only saved 17 gallons!

This is the problem with using miles per gallon (MPG) to measure fuel economy: the same increase in MPG (in our example 3 MPG more) does not mean the same amount of gas saved. The amount of gas saved depends on both the MPG number and the change in the MPG. Having to think about both the number and the change is unnecessarily complex. Using gallons per hundred miles lets us use just one number again. Let's see the example again, but this time using GPHM.

In 2008, the Jones' Ford F150 used 10 GPHM, and the Smith's Prius used 2.5 GPHM. After the mechanical tuneups, in 2009 the numbers were 7.7 GPHM for the Jones' and 2.33 GPHM for the Smiths. Now you can see the big drop (2.3 GPHM) for the Jones' compared to the tiny (0.17 GPHM) gain made by the Smiths.

So think about fuel economy in gallons per hundred miles (GPHM) instead of miles per gallon (MPG) and you will have a better idea of what is really going on!

Best In Class Gas Sippers of 2007

If you are thinking of getting a new car and want to save on gas at the same time, you might want to think about buying a used car. After a couple of years, the sticker shock price on cars comes down, so buying a 2007 model can save quite a bit of money. At the same time, you have a car that is almost new. When looking over what is available for the 2007 model year, you might like to know what is the most fuel efficient vehicle in each class. Here is the official EPA list.

For each major class of vehicle, this table gives the make and model (for the 2007 model year) that gets the best gas mileage. It also includes the city and highway mileage estimates for that model.

2007 Model Year Best-In-Class Fuel Mileage

Class	Make/Model	City/Highway
Two-Seater	Mazda MX-5 (manual)	25/30
Minicompact Car	New Beetle Convertible	22/30
Subcompact Car	Toyota Yaris (manual)	34/40
Compact Car	Honda Civic Hybrid	49/51
Midsize Car	Toyota Prius (hybrid)	60/51
Large Car	Hyundai Sonata (manual)	24/34
Small Station Wagon	Honda Fit	33/38
Midsize Station Wagon	Ford Focus Wagon (manual)	27/37
Sport Utility Vehicle	Ford Escape Hybrid FWD	36/31
Minivan	Dodge Caravan 2WD	20/26
Pickup Truck	Ford Ranger Pickup 2WD (manual)	24/29
	Mazda B2300 2WD (manual)	24/29
Van (Cargo&Passenger)	Chevrolet G1500/2500 Chevy Van 2WD	15/20
	GMC G1500/2500 Savana 2WD Cargo	15/20

EPA Fuel Economy Labels

Cars sold in the US are required to display a fuel economy window sticker. This allows consumers to see the estimated mileage per gallon the vehicle gets in both city and highway driving. Consumers can use the information to compare different vehicles. Starting with model year 2008 the format of this information as well as the tests used to derive it have changed. The changes are in response to consumer demand for better information. In particular, the newer tests account for faster driving speeds and greater acceleration. They also take into account usage of the air conditioner and colder outside temperatures.

Looking at the label itself, you can see the two estimates for city and highway driving on the two sides. In the center is the cost of gassing up the vehicle for a year, based on an estimated price of gas and driving distance. Your numbers will be different, especially the cost number. It is hard to get mileage much better or worse than the estimates, but it is easy to drive much more or less than the estimated distance. Also in the middle, below the annual cost of gas estimate, is a bar with a triangle pointing to an overall mileage combining city and highway values. It shows on the left and right ends the range of MPG values for vehicles in the same class, for example SUVs or light trucks. This lets the consumer see how the vehicle stacks up against similar choices.

The choice of vehicle has a big potential to allow you to save on gas. Don't ignore potentially helpful information on the fuel economy labels!