Maximum miles per tank

Math. That’s another way to figure out the maximum miles from a tank, ahem, bladder of gas in a Prius.

Each fill-up of gas directly yields two numbers: miles driven and number of gallons to fill the tank. Divide the first by the second gives the actual mileage (mpg). Subtracting the number of gallons to fill the tank from the ideal maximum capacity of the tank—11.9 gallons—yields the number of gallons of gas in reserve. Multiply that result by the actual mileage, add the product to the number of miles already driven, and the total is the maximum number of miles one could have driven with that tank of gas.

But wait. There’s a difference between the actual mileage and the mileage displayed by the Prius. (See displayed versus actual mileage.) Do the same calculations again, except multiply the number of gallons in reserve by the displayed mileage.

These two sets of calculations give a range for the maximum number of miles one could have driven on a full tank of gas. This range is the upper and lower limits for maximum travel distance from a tank of gas based on actual (calculated) and displayed (computed) mileage (not respectively).

The results aren’t pretty. Granted, the results are not all over the map, but neither are they a smooth curve. Funky data (a.k.a. outliers) stick out. The varying band of results, narrow to broad and back, showing the upper and lower limits of “maximum” might be too erratic to be useful. However, the chart definitely shows that travel distance from a tank of gas is cyclical, varying by season. The maximum number of miles from a tank of gas increases during the warmer months (despite in my case the use of air conditioning) and decreases during the colder months.

The maximum number of miles from a tank of gas seems to be about 540 to 580 miles during the summer, and between 480 and 520 miles during the winter. It’s safer in terms of not-getting-stuck-in-the-middle-of-nowhere to stick with the minimum number, and then some, when determining how many miles to drive on a tank of gas. In my case, 450 miles from a tank of gas seems about right.

7/2/11 I have no idea why that thick band at 45° is appearing in the chart that follows. All these charts about my Prius come straight out of a Microsoft Excel spreadsheet. None of the other charts have this problem.