Onboard MPG Averaging Interval, User Reset, and Behavior
I been enjoying (sometimes) the game of coaxing higher MPG on the fly, looking at the onboard computer. I'm familiar with how the ability to change any mathematical average gets less over time (I run distance, and watch my pace - near the end of a long run, one can effect much less change to the average, up or down). That's basic math. However it seems with the Niro as if it averaging period "maxes out" to something less than the entire tank distance -- seems like maybe the last 100 miles or the last 2 hours or something like that. I get this behavior that if I try to, I can get the avg MPG up to about 48 in a dedicated hour or two, *regardless* of what happened before. My most recent tank was a good example. I had 1000+ lbs of passenger and cargo, a few hours of 75 MPH+, several hours of steep up and down dirt roads, with expected low average MPG numbers displayed. Then in the last hour, I got the MPG display coaxed up to 48. But as suspected, that was way off as my fill-up at the end calc'd 42.5 MPG (485 mi/11.4 gal).
This prompted me to dig into the manual. Turns out the average period has options for resetting: (1) manual (2) auto - when car is off for 4+ hrs (3) auto - when car is driven 1 mile after putting 6+ liters in the tank. I thought AHA! that's it, my average must be set to option (2), in effect resetting for every trip! But NO, it was set to (3), so the behavior I'm seeing can't be easily explained. My first tank matched the computer quite closely (46.9 MPG); but on that tank, fuel economy and what I asked the car to do over the tankful was quite even/steady.
I know the computer isn't gonna have the most accurate answer, but it seems the algorithm might be a bit flawed, or at least different than described. If I really want to dig into it, I presume I could record each individual trip miles and MPG (the data that displays briefly on shutdown), then average those numbers (weighting each for miles in that trip), and then see how things compare to both the onboard computer and actual reconciled (like Fuelly does, which is a simple division). Ah, we'll see if I'm actually that dedicated.
But perhaps more importantly, the car behaved great with 1000+ lbs in it on steep rocky roads and such. More on that in a separate post.