What's the optimal interstate cruising speed to achieve the best MPG?

 

From what I've gathered 65 or under (which is hard in this car).
Your mileage may vary

 

Technically driving 55 mph will offer the better MPG but I doubt most drive that speed.

There are a lot of variables to consider but the way I achieved my best MPG of 38.4 MPG on the highway was by periodically watching the average MPG on the OBC once I saw that figure and it wouldn't go any higher I maintained that speed approx. 70 mph by setting the cruise control.Keep in mind that was in an automatic with luggage while I was traveling from South Florida to Minnesota and back.

 

Someone with a scangaugeII could chime in, but I'd guess the best MPG for a MC is probably around 45-50 mph. Probably 45 actually. That seems to be the best speed for most cars I've seen in hypermiler forums. I can confirm after our car is delivered.

 

I recently drove my car to Maine and back. On my first tank of gas which took me 576 miles from NC to NJ, I cruised at a maximum of 73 indicated (70 by GPS). There were also stretches where I cruised slower when the speed limits were lower. I averaged a hand calculated 40.1 MPG (41.6 on the trip).

 

I did a 200 mile interstate run and had my OBC say 49.7 mpg. (My OBC is 2-3 mpg optimistic) I cruised at 65 (w/cruise on), no ac, and window about half way down, tires +1 psi over recommended.

Air resistance goes up by the square of the speed, and as such speed increases will have a more pronounced effect as the speed goes up.

 

+1. I believe the "knee in the curve" of aerodynamic drag versus fuel efficiency is in the mid-40s mph. Of course, this assumes a certain engine /transmission efficiency and road friction, level ground, no acceleration, etc. If you're climbing steep hills in high gear into a stiff wind with under-inflated tires at 45 mph you're obviously not going to win any mpg contests...

 

My impression is that 45 is about optimum, but I haven't analyzed it carefully. Turning the AC off is important for mpg.

I have a ScanGaugeII, but you can see instant mpg figures on any MINI by setting it on your tach readout. See your manual for changing the readout.

 

right, but the scangauge does a better job of keeping trip mpg ave, day mpg ave, yesterday mpg ave. It also can do MPH averages. Makes it easier to try a trip at 45 average and another trip at 60 MPH average... that's where I'll need to experiment, if someone else hasn't already done it.