Announcement: please post your average speed and temperature when posting about fuel consumption

Since I got the new Prius, I don't actually know where the average speed and temperature is located.

On the old Prius it was on the tripmeter. Please let me know and I will post it. I always keep track of my tank miles on Trip A.

 

Wayne Gerdes at cleanmpg.com did a speed vs mpg plot for the Gen 4 ECO 2:
2016 Toyota Prius First Drive Review - First Drive Results | CleanMPG
It's no surprise that mpg is very sensitive to speed. After all, loss of energy to form air drag goes as the square of the speed (according to the basic model), and other losses increase with speed as well.

Wayne does not say, but I imagine this plot was done with the gas engine running. If so, especially at speeds in the 50-60mph range where the EV provides nearly enough oomph to maintain speed, one might do much better the more one can persuade it to run in EV.

Incidentally, from Wayne's plot one would expect steady state 60mph to yield roughly 64mpg, and steady state 40mph to yield something over 80mpg.

As for temperature, by now most people here are well aware that higher temps mean better fuel economy, at least up to the point where AC is needed and that loss factors in. Incidentally, I think that the temp shown on the upper right of the screen is the current temperature rather than some average. But I am not sure what an "average" temperature would mean anyway.

As for average speed, it seems unlikely that 60mph average reached by driving some at 80mph and some at 40mph would give the same mpg result as driving 60mph the whole time.

If someone gets a high mpg reading that is useful to me because it expands the performance envelope of the Prius. It's already clear to me that the speed must have been reasonable and the temperature favorable.

 

ouch! calling out the hyper milers!

 

Cruising or maximum speed would be more useful than an average.

Another piece of data needed for claims to be meaningful would be altitude change for one-way trips. That is, if you scored 110 mpg on a short downhill jaunt, I'm not impressed.

 

FYI:

Actually the model is:

• drag_hp = (mph * (Target_Coef_A + (mph * Target_Coef_B) + (mph * mph * Target_Coef_C) ) + overhead
  • Target_Coef_A, Target_Coef_B, Target_Coef_C - comes from EPA "Test Car List Data Files"
  • overhead - has to be measured and is the HP equivalent of the vehicle electrical overhead
• Brake Specific Fuel Consumption - is the fuel consumed per unit of power.

But any model needs validation or test points to make sure no one has made a mistake.

I incorporated Wayne's and other open source metrics to validate my 2016 engineering model:


This engineering model is based upon the EPA roll-down coefficients and thanks to the extensive testing, we have the same data for the EPA tested, 2016 Prius family:

The reason for having a model is we can project performance of multiple Prius variants with the changes that the EPA used in their testing. This separates vehicle performance from ordinary, individual variability.

Now one of the best things about having a model backed up by benchmark data is to diagnose problems with a car. I've done this since 1971 when I bought my first car, a used 1966 VW MicroBus. It is also how I also tell if someone wants to diagnose a MPG problem or just came here to b*tch.

GOOD LUCK!
Bob Wilson

 

Then press the trip button (the left one) to toggle between A, B, since start, and lifetime summaries.