MPG in long and short term memory display

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Active member
Aug 8, 2017
The long-term and short-term memory stats that are displayed were always a bit confusing to me. All electric is always 300 mpg. The long-term mpg was more interesting but seemed too low to me. It seemed in both cases that the calculations were imputing some “gallons” into the electric consumption.

Here’s what I finally worked out in my case. During the time I have had the car I have had the following:

14740 miles total
4550 miles on long gas-only trips
10200 other miles (around the metro area, mostly stop and go)

I have found that the KWh/100 miles is quite efficient on the car. My long-term memory display
shows 24.8. I see a similar number in short-term memory driving around town on all electric. Using the EPA’s assumption of 33.7 KWh/gallon of gasoline and thus dividing 33.7 by 24.8 yields an mpge of 136. I attribute this better-than-advertised number to all the regeneration from the mainly stop and go driving.

My long-term memory shows 65.5 mpg. How did they get to that? I believe they add “gallons” for electric usage at the real mpge of the car. Let me explain why I believe that.

I will use 36 mpg for my real gasoline driving mileage. That’s about what I’ve seen on the long trips pounding the interstate at 75 mph and also when I’m driving around a town short-term at a trip destination without charging opportunities.

Looking at the last 1000 miles display regularly over the various times between long trips, my electric vs gas usage is around 90% for me depending on the season. It turns out that assuming 88.5% gives the exact number that the long-term memory display is showing me. Here are the calculations:

4550/36 mpg = 126.39 gallons on long trips
10200*.885/136 mpge = 66.59 electric “gallons” non trip
10200*(1-.885)/36 mpg = 32.69 gas gallons non trip

126.39 + 66.59 + 32.69 = 225.67 total “gallons”

14740 total miles / 225.67 “gallons” = 65.51 “mpg” which is right on par with the long-term memory display of 65.5.

Anyway, I feel better having done this. I finally feel like I understand the displays.

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