Speed vs. Fuel Economy

[Arragonis]

Comparison in the Prius - Mrs A and I had to travel down south recently and the start and end points were both at pretty much sea level - we used the same route on both occasions. On the way down I kept a high-ish average speed as we were in a hurry to do the trip in a day before some forecast gales struck the UK. Average (on the on-board computer) was only 42 MPG.

On the way back Mrs A took it easier, the average being 10 MPH lower (we filled up at both ends and reset the trip) - average was 49.

Actual speeds withheld to preserve licence point status

[Old Tele man]

...driver to officer: "...But, Officer, I wasn't speeding ALL the time..."

[ShadeTreeMech]

I know my maxima, when it was running good, got excellent fuel economy running nonstop at about 80. While it seems perverse, I think it hits a fuel economy sweet spot about 2500 rpms, so coupled with it being in the highest gear ratio, plus some cautious drafting, I managed to get 30 mpg on a tank.

Sadly though, I rarely can go that fast regularly, nor that nonstop.

[Ladogaboy]

I've improved the aero on my car a little (not enough, obviously), but the sweet spot for me should be 55-57 mph at this point. I rarely have a chance to cruise at that those speeds on level ground, since the freeway speeds here are typically 65-70 mph. What I have found is that the difference between 65 and 75 mph is ~ 4-5 mpg (17% difference).