Most efficient speed for best MPG?

We all want to drive faster. We all want more MPG. Why not have both?

My solution:
I find on long highway trips it is good to draft behind a large fast moving vehicle like the following:

Semi Trucks - plenty to choose from, the square trailer trucks are good except they tend to kick up rocks sometimes.

Big Travel Buses - best draft wake, does not kick up rocks.

Large motor homes - good draft wake

Large 5th wheeler trailers - good draft wake but tend to be slower and tend to waggle in the wind.

On my last road trip I was doing 41mpg at 65mph in a headwind. I drafted behind a Travel Bus and was doing 50mpg at 75mph.

You do have to pay close attention but I find the cruise control can do much of the work by just bumping down and up as we traverse hills. I keep my foot over the brake to disengage at any time.

Any thoughts?

 

There have been many discussions and performance graphs on this. I earn optimum fuel economy, dependent on ambient air temperature, at 48 mph in my daily commute (30 mi each way, mostly level). I earn higher with higher temperatures, and don't drop below 48 mpg during winter. I keep detailed track of distance and fuel using a spread sheet.

 

The best speed for MPG is 25-37 MPH

 

depends on the vehicle

2001 Crown vic gets 26 MPG @68 MPH, but only 18 MPG @45 MPH
2007 Prius got 65 MPG@ 65 MPH behind a flatbed semi for 300 miles, best MPG is between 45-50 if you can maintain it on a flat road, but in reality, not so easy.
2009 Camry Hybrid, 41 MPG @65 MPH, 38 MPG@55MPH.

Seems like a lot of people are hung up on old 1970's way of thinking 55 is more efficient than 65. That held very true back in the 70's and early 80's when cars were built like bricks, but an amazing thing happened when computers were used to design cars, they became aerodynamic, and are now more fuel efficient at higher speeds. Add into that the advent of 4-5 and 6 speed transmissions with overdrive, fuel management computers, and better designed tires, and cars are nothing like they were when the 55MPH limit was imposed.

Like I said, it all depends on the car. The Prius would probably get better high speed MPG if the engine were a little bigger, it works too hard at higher speeds. It's perfect for city driving since the electric motor does a lot of the work, but on the highway the electric motor is limited in what it can provide so the gas engine is on its own.

 

I'm starting to settle on 44 or 49 mph for most terrains. Of course time and traffic can dictate other speeds. I try to set the cruise control to these speeds.

 

I know I will get better mpg if I slow down, but I have settled to drive around 60mph. That speed gets me around 48mpg. If I slow down to below 50mph, I can get over 50mpg easily. Time is also important to me so 60mph is good enough. I dont need to chase any efficiency crowns.

 

I don't know if there is any "efficient" speed. After all the normal efficient driving methods and tires etc are taken care of, I think external wind speed and direction is a big factor in what MPG is achievable.

For example I can get between 67 - 94 MPG (US) (80-113 MPG (UK) / 3.5-2.5 l/100 km) at 64 mph (104 kph) and other days I can't get better than around 47 mpg (56.5 MPG (UK) / 5 l/100 km) on the same journey.

Interestingly, on the days I have problems there is wind. Also, going slower does not seem to help much. On calm days, I can go faster without much of a penalty, and even better if there is a large vehicle I can follow behind (at a 2 sec gap or even 3). On a windy day, there is almost no benefit in drafting in this manner.

YMMV.