The "1/2 MPG Per 5 MPH Rule" Really Is True

[Aufgeblassen]

I've always heard that you lose 1/2 MPG for every 5 MPH you increase your speed.

The other day with an MT trailer I determined my MPG @ my nominal travel speed of 60 MPH, and found it to be to be 8.9. I then increased my speed to 65 MPH, and sure enough, it dropped to 8.3 MPG.

Unless you actually are in a hurry to get where you are going, you are foolish to drive more than 60. So what if it takes you 10.8 hours to get where you are going instead of 10?

[Steel Horse Cowboy]

I've always heard that you lose 1/2 MPG for every 5 MPH you increase your speed.

The other day with an MT trailer I determined my MPG @ my nominal travel speed of 60 MPH, and found it to be to be 8.9. I then increased my speed to 65 MPH, and sure enough, it dropped to 8.3 MPG.

Unless you actually are in a hurry to get where you are going, you are foolish to drive more than 60. So what if it takes you 10.8 hours to get where you are going instead of 10?

I believe I have already made this point in a different thread. You should save on average $150-$175 a week in fuel based on 2,500 miles and 60mph vs 70mph.

There is plenty better things I can spend $150 each week on than fuel and getting somewhere 30-45min earlier.

Not to mention how much easier it is going 60mph and letting everyone pass you. Driving actually gets easier.

[solo379]

That's probably how Columbus felt, when he discovered an America! To tell you the truth, it's a bit more complicated than that, but talking ABC, you are correct!

[Aufgeblassen]

Not to mention how much easier it is going 60mph and letting everyone pass you. Driving actually gets easier.

My sentiments, exactly. When we 1st got our Class C RV, some 10 years ago, I drove it 60 MPH, because it is such a huge cross sectional area into the wind. It is so incredibly relaxing just driving, and rarely having to worry about passing anybody. 60 MPH is really not that slow. A trip from Orlando to Chicago takes only two days, stopping around Chattanooga for the night.

[allan5oh]

I have found 8/10ths per 5 mph is more accurate for my setup. I have the testing #'s on this site somewhere. I found 5 mph made 3X as much difference as going in and out of the sweet spot.

[Aufgeblassen]

I have found 8/10ths per 5 mph is more accurate for my setup. I have the testing #'s on this site somewhere. I found 5 mph made 3X as much difference as going in and out of the sweet spot.

The "sweet spot" is a fallacy. Within the so-called sweet spot, you will find much higher fuel consumption at the high end of it vs. the low end.

Both my 8.9 MPG & 8.3 MPG numbers were in the S/S.

[allan5oh]

I agree, simply running the engine at lower rpms will get you better mpg even if you're below the sweet spot. The sweet spot is just a compromise between driver satisfaction and engine efficiency.

[heavyhaulerss]

There are times where it makes sense to drive slower. when I used to leave out sun to go 600 miles I would drive 62 mph 7 55 in mi- oh, I calculated 2 runs a week would save me 800 a month. there are time where I run short hauls & can do 3 in a day. in those circumstances it would not make sense for me to save $10.00 on fuel, but lose a $300.00 load. one place I go to receives until 10 p.m. if I get an early start I can get 3 loads off, but I have to hustle & that means 68-72 m.p.h. though even on short runs if I am not pressed for time I will do 60-62-65