Four Year Progress Report

Your lifetime and average mpg seems to be increasing. Does that mean you're continuing to improve your pulse and glide technique?

 

Hi Tony,

I want to know how you managed to drive on your original equipment tires during four winters in Chicago, without getting into a serious accident...

Seriously, congratulations on your steadily improving mpg record!

 

Congratulations, Tony!!

Thank you for taking so much time to share your experiences and to offer helpful advice. My Prius ownership experience is much the better because of your great contributions through PriusChat.

 

dang tony! i'm impressed at those mpg numbers.

i also can't believe you're still on the oem tires... we just put on our 3rd set. do you use high psi in your tires?

 

Tony, how long have you run 52/50 in your tires?

 

The relationship of MPG vs. Ave. Temp. is impressive. Folks should click on the image to view it full size to really appreciate it. You've illustrated a response of about 0.4 MPG/degree F over the range from 20-70 F. I expect that somewhere above 75 F the mileage would begin to decline again.

 

I'm sure that the correlation is stronger than that if you were to factor in/out the improvement in efficiency with time and air pressure. Rarely do you get process correlations that are so strong and so obvious.

 

Just wondering why you would have this expectation.

I don't have any data to back this up (well, I only have my own mileage numbers), but my experience shows that mileage goes up as temp goes up, even into the 80s and 90s. We've had cooler mornings of late, and I've noticed my morning MPGs are a bit lower than they were in July and early August.

 

There are several reasons to anticipate a mileage drop:
1. Primarily due to AC demands for driver/passenger comfort. (Depends heavily on humidity and comfort level requirements of the occupants.)
2. Traction battery somewhat outside of its comfort zone--if the battery is hot the system is reluctant to charge is my understanding.
3. Rolling resistance should increase as asphalt and tires become "stickier".

I was intentionally non-specific ("somewhere above 75") with the temperature at which efficiency would begin to decline. Quite a few folks have noted falling mileage as it gets hot and by 100 the complaints appear general.

Yes, it has been cooler in the morning in much of the Midwest (59 was the low locally yesterday), well below the "above 75" region I vaguely motioned toward, and I would expect that to require more ICE operation to get the systems to temp. Tony's graph illustrates the temperature relationship well up to about 70+.

There are a lot of variables that would go into determining where the break point was, but a meticulous plot like Tony provided should show one if he ran his same routines at ever higher temps.

There are so many variables that I would expect to influence the result: driver's comfort requirements (AC set at 70 vs. 75, 78, etc.), humid or dry, length of route, speed of route, garaged or outdoor, sunny or shaded parking, asphalt or concrete road, etc. The combinations will likely be controlling: occupant comfort requires less AC work for ambient of 90 F and dry than 90 F and humid. Short low speed drives in town traffic during hot humid weather will use a much higher fraction of the car's energy for AC than long stretches of open highway in the same weather (or so I suppose.)

I sort of expect a large dead band (say 10-30 F, maybe more) where there will be no statistical difference for a large pool of drivers in different regions. However, that doesn't mean that individuals would not notice substantial differences in their normal routines over a tight temp span.

p.s. Does anyone know what temp./range/target/deadband the car is using for the traction battery? I would expect that to factor in prominently in finding the break point--just behind occupant comfort settings. But I'm guessing of course.