Personal MPG experiment

Thanks, jamgolf. It's always satisfying when experience confirms what you think. Speed is the enemy of fuel efficiency.

 

Thank you very much!

I've added your data to this graph:

For reason's I've never understood, I've not found anyone else who plots actual, measured, MPH vs MPG yet the data is so terribly useful. <sigh>

Bob Wilson

 

Seems to match my experiences as well!

Thanks for the plots, Bob!

 

Thank you as well. I agree 100%, speed cost money.

 

Power to overcome aerodynamic drag increases by the speed cubed. In other words, it takes eight times as much power to go twice as fast, just looking at aerodynamics and the faster speed (power = speed * drag, drag ~ speed^2).

Tom

 

Thats a nice experiment with some great numbers you got! Out here in the bay area either the traffic barely moves (bumper to bumper) else the it moves way too fast (in excess of 75 mph). I wish i could add some more terrain into these numbers. Cheers!

 

OK, I did my own experiment this weekend, although not nearly the detail.
2008 Prius, has ~2000 mi.
Drove from Houston to Waterwood (Lake Livingston) and back - 96 mi each way. Myself and two passengers (wife and 10 year old).
From Houston:
93 F outside, A/C set to 77 inside.
On the way up, drove between 60-65 mph. Accelerated down hills and approaching up hills in order to build momentum. Coasted up hills to avoid uphill acceleration.
Result: 53.3 mpg

To Houston:
On the way back, had sister-in-law along (so had myself and 3 passengers). So to avoid inquisitive remarks by her about my driving, I figured I'd drive the way I "used to".
91 F outside, A/C set to 76.
Drove 65-70 mph, avoided using any hypermiling techniques.
Result: 45 mpg.

Calculated from the MFD. My experience so far is that my actual mileage is about 2 mpg below the MFD.

So yes, slowing down did have an effect! Although I was hoping for slightly better numbers than this. I get well over 50 going to/from work (half highway, half 35/40 mph roads with stoplights about every 1/2 mile or so. Try to pulse/glide and coast to stoplights whenever traffic allows, which is not often in Houston!).

 

At 65 mph, I expect ~52 MPG and at 70 mph I would expect ~49 MPG on cruise control on I-20 at 70F. Your numbers are well within the expected range under the higher temperatures and AC load.

There have been some investigations of hill climbing speeds and so far 55-60 mph seems to be best at avoiding inefficient engine power settings and drawing on the battery. Above 65-70 mph the engine has to work at inefficient power ranges when climbing a hill and the vehicle will draw energy from the battery. One of the best ways to drive hills is to follow a heavily loaded truck at a safe distance. Just match their speed profile.

Bob Wilson