Prius Speed vs MPG: Inconclusive

I had a roadtrip looming, so I figured I’d do some experimentation:

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I wanted to find which highway speed would give me the best MPG.  I had some hilly areas (Louisville->Cinci) and some flat areas (Cinci->Columbus) to experiment with.      I figure after 10 miles, I’ll get an okay reading for average mpg, and I could move on, right?

Wrong.  

Turns out, the relative altitude of the car makes a HUGE difference.  If I reset my trip-meter at, say, 700 ft above sea level (as measured by my cellphone GPS), then at 600ft, I might have a MPG of 62, and at 800 ft it might be 57.  Even after 15 miles.  

I could have worked with this, except that every time I seemed to reset the trip meter, I never got back to that same altitude.  The road went down.  Or it went up.

Now given some fancy math I’m sure I could have calculated some numbers.  But not worth it. 

Thanks to some really slow traffic, though, I did figure out that in general, the Prius wants to get about 70MPG for anything over 45 mph, with the AC on, except that wind resistance knocks that number down to about 45MPG at about 70MPH.  

It seems that driving with the cruise set at 55 nets me in the low 60MPG’s. 

It does not appear there is a local maximum somewhere between 50 and 60.   50 is more efficient than 60.  And that is NOT a speed I’d set my cruise control to, sorry.  I don’t want to be one of THOSE Prius drivers.

Maybe some day when I’m bored I’ll drive a loop (I264, I71, I265, I64) at 50,55,60,65 MPH and record those numbers.   I can use the straight stretch near the ford motor plant as the transition from one speed to the other.

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