How far should you go in search of cheap gasoline?

I took a long drive on the weekend and refueled for the first time in a long time. I joined Esso, Mobil and General’s “Speedpass” at the end of the year, and it’s very convenient.

There is an Esso on the main road in my neighborhood that I pass relatively often, and I use it frequently, so it will continue to be useful.

Is it rational to walk from one gas station to another in search of even one yen cheaper gasoline?

However, after all, I am a lazy person, and when I run out of gasoline, I just go into any gas station that catches my eye without thinking about the price, but there are people in the world who are looking for a cheap gas station for even one yen.

I often see crowds of cars standing in line in front of cheap gas stations. Whenever I see this, it really annoys me and I often wonder if this is really rational.

I mean, it’s only a difference of about a can of coffee, don’t you think?

But can you really say they are not rational? Isn’t it actually they who are not rational?

I’ve decided to take a serious look at it tonight when I’m relatively free.

Analysis 1: How many liters do you gain per yen?

For starters, let’s look at how many liters you gain per yen.

The premise is.

• クルマの燃料タンクは満タン時50リットルとする
• 基準となるレギュラーガソリン価格を143円とする

By the way, I referred to this site for the regular gasoline price as a standard.

Based on the above assumptions, the following results were calculated for each gasoline unit price: “price when filling 50 liters,” “difference from the standard (143 yen per liter),” and “conversion (of the difference) into liters.

A. Unit price (yen/L)	143 yen	142 yen	141 yen	140 yen	139 yen	138 yen
B. When you put 50l	7,150 yen	7,100 yen	7,050 yen	7,000 yen	6,950 yen	6,900 yen
C. Difference from standard	0 yen	50 yen	100 yen	150 yen	200 yen	250 yen
D. Converted to liters (C/A)	0.00L	0.35L	0.71L	1.07L	1.44L	1.81L

The following is a rough explanation of the table and the calculation results.

5円安い →　「250円お得」「（ガソリンに換算して）1.81リットルお得」

That’s what I’m talking about.

It’s not as good as a Starbucks latte, but it’s about as good a deal as a Doutor latte.

Verification 2: How many kilometers should we aim for a stand that is as cheap as one yen?

Now, it’s time to get down to business. Yes, it’s important to know how hard you have to work to find it.

Although it is a good idea to drive your car in search of the cheapest gas station, you use fuel to get there, so it is meaningless unless you properly consider the reduction in fuel consumption.

In our earlier example.

「5円安いスタンドを目指したが、そこへたどり着くまでに1.81リットル以上使ってしまった」

If it is, then it makes no sense at all.

Therefore, the distance that it would be reasonable to travel in search of a cheap gas station is

「5円安いスタンドであれば、そこへたどり着くまでに使用するガソリンが1.81リットル以内であればよい」

That’s what I’m talking about.

Now the point here is the fuel economy of the car.

Yes, by using this fuel economy, you can convert “liters gained (by spending a penny less)” into “miles driven gained”.

「得した走行距離（km）」＝「得したリッター（L)」×「燃費（km/L）」

In other words.

1円でも安いスタンドを求めて移動した距離がこのように算出される「得した走行距離（km）」以内であれば、その消費行動は「妥当である」

So we can say.

Since you are actually going to that gas station and coming back, the “Marginal Value Driving Distance (km)” that you should go out of your way to get the cheapest price is half of the “Gained Driving Distance (km)” that you calculated above.

「限界お得走行距離（km）」＝「得した走行距離（km）」÷ 2

Here is the calculation of the “Marginal Value Driving Range (km)” defined in this way, by cheapness and fuel consumption.

fuel consumption	small enough to be relieved of one yen	2 yen cheaper	3 yen cheaper	4 yen cheaper	5 yen cheaper
10km/L	1.8km	3.5km	5.4km	7.2km	9.1km
15km/L	2.6km	5.3km	8.0km	10.8km	13.6km
20km/L	3.5km	7.1km	10.7km	14.4km	18.1km
25km/L	4.4km	8.9km	13.4km	18.0km	22.6km
30km/L	5.3km	10.6km	16.1km	21.6km	27.2km

A quick explanation of how to read the table again.

例えば「燃費が20km/Lのクルマ（表のちょうど真ん中の行）」の場合には、

• 1円安いスタンド　→　3.5kmまでならお得
• 3円安いスタンド　→　10.7kmまでならお得

The result is the following.

Verification 3: Checking with actual maps: normal cars

It’s hard to understand with numbers, so let’s look at the actual map.

Well, for example, the fuel consumption of my car is about 10km/L to 12km/L.

If it becomes it, and it is a table of what area it should look for all the way if it is a cheap gas station for 2 yen, and it is earlier, the “limit economical running distance (km)” becomes about 4 km.

If I show this on a map with Musashi Kosugi Station, the nearest station to my apartment, as the center, it will look like this.

It seems to be a rather realistic range.

この程度であればすぐ発見したスタンドにはいっても大差ない気がします。ということで、私が普段取っている「見つけたらすぐ入る」って方針は結構妥当的であったといえるのではないでしょうか。

Verification 4: Confirmation with actual map Hybrid vehicle version

But it turns out that this is pretty amazing when it comes to the level of “hybrid cars” that are becoming mainstream these days!

With a fuel economy close to 30km/L.

• 2円安いスタンド　→　10.6kmまでならお得
• 5円安いスタンド　→　27.2kmまでならお得

and the range of action becomes much wider.

I’ll try to display the same map, but since it goes all the way to the ocean in Kawasaki City, here’s what I’ve done with Machida City in the center, based on my own judgment and prejudice.

The central blue area has a radius of 10 km and the large red area has a radius of 25 km.

単純な試算だし同心円が直線距離で書かれているとはいえ、町田市在住のハイブリッド車オーナーな方は、5円くらい安いのであれば世田谷とか藤沢とかまで行って入れても「お得」ということになります！すげえ…。

I don’t think anyone would go to this much trouble, though (laughs).

summary

It’s been a long post. I guess this is how I sum it up.

• 燃費が10km/L前後のフツーのクルマ　→　見つけたらすぐ入ったほうが妥当
• 燃費が20km/Lを超える最新のクルマ　→　ちょっとでも頑張って安いスタンドを探す価値アリ

It was kind of very informative, even if it was a simple estimate. In any case, I’m relieved to know that as long as I’m driving my current car, my grubby decision is valid (laughs).

In my case, even if I were driving the latest high fuel efficiency car, I would probably buy a canned coffee or something at the gas station, so I feel like this kind of saving would end up being useless.