I would have thought that in my 2010 Lariat at 50mph that the tranny would be or should be purring along in 6th gear and giving me maximum fuel econonmy. But after an hour or so I went to look on the computer and it show those fuel economy bars at 2, but my rpm was just below 1500. Ya just can't win. FS

 

Every setup is different. Tires, gears, what the truck is carrying, terrain, wind, etc. I have found that generally, my truck gets the best mpg at about 67 mph, on cruis control. If I go slower, it has to work too hard to get up the hills even though the rpms are lower. Two things that really eat up my average mpg is wind and idleing. Going into a head wind of 10-12 mph can cut my average mpg by 2 mpg. I was amazed.

 

Right around 70MPH is where aerodynamics really start to become a factor. Ever wonder why performance cars with deployable spoilers all are activated between 65-70? Wind resistance is also not a linear force it's logarithmic.

Idling is bad because you are burning gas and not moving. MPG is an average of distance over consumption. If the consumption keeps going but the distance doesn't change the average goes down.

 

Sounds like you were lugging her down to low. Did you go up to 55 and see a change?

 

Funny you should mention that your truck seems to be better mileage at 67mph. I think mine gets good mileage at around that speed. I'll try is out at about 70 when I hit the highway later this week. FS

 

I drive to Canada frequently, around 630 miles at 75 to 80, mostly on cruise control. All highway. Best i ever got is 16.8. But at that speed, whaddya want?? :-). I can't bring myself to only drive the speed limit....

 

[QUOTE=Wookie;4715082]Right around 70MPH is where aerodynamics really start to become a factor. Ever wonder why performance cars with deployable spoilers all are activated between 65-70? Wind resistance is also not a linear force it's logarithmic.


Actually it's exponential. When minimizing the drag on the truck, the one component the driver can control is velocity (speed). Coefficient of drag, air density and wetted area are constant. Since the drag of an object moving thru the air increases with the square of velocity, you can see what a big impact speed has on the value. Therefore, if you double your speed, say from 35mph to 70mph the drag increase by a factor of 4 (2 squared = 4). It takes power to overcome the drag and power equals fuel.

Now, jack your truck up or put something large in the bed and you now are increasing the Cd and wetted area......drag goes up.......fuel guage goes down.

Sorry about the geeky engineering talk, but aerodynamics is fun

 

Awesome! Explain "wetted area"...