dplummer87

<2000 for me as well. 55-65mph is awesome. Once I hit 70+ and get into the 2100-2300 mpg range with it on cruise it drops to about 15. The best i have achieved is at 65mph on I10/I20 across texas I got about 19 on open flat highway with cool weather no wind.

Thunderslide

so you have a chance at that number, 2-3 times a year?

aidswolf

would it not make sense that just.. the lower your rpm the better mpg.. therefore get it as low as possible for cruising.

tiger&lionGSP

Yep I try to keep my under 2000 rpm also. I am running 33 and I am getting about 14-17 mpg around town. I am using shell gas. I am going to switch back to stock tires and check ,milage again with my topper on and off.

dplummer87

Ha! Maybe once! Seeing how I have to get on I-10 and then possibly I-20 depending on where im going and go minimum 600 miles to get to the next sign of life, I do try to keep it under twice a year.

'08f150stx

Personally, driving on a flat straight is great for maxing out mileage but isn't real driving conditions. I found more recently is that around 63 to 64 mph (gears and engine below) is just around 1600 rpm is where I max out in regular driving conditions. It is highway with no stops but that is all. The salesman when I bought my truck told me the 4.6 will just barely get better mpg, but it seems the 5.4 does. I contribute that to the higher torque so the engine doesn't have to work as hard.
(I did just get 18, and that was with a load of firewood in the bed but the speed was barely under 65 with the cruise on)

BassAckwards

33" Tires and a wheel/tire combo weight of 85lbs with 3.73. and all other mods seen below.

My Edge shows an IMPG of 25 when going down my County Road to my House which has a speed limit of 40 and I set the edge to lock the TC at low speeds so I set cruise at 43mph and am only doing 1020 RPM

Jmfalcon1

I've got a 2005 5.4 SCrew 3.55. I do 79 mpg in between Wichita and KC (180 miles). I average 17.5 mpg on that run through the Flint Hills (closest thing we've got to mountains). Low RPM's isn't the only determining factor in MPGs, you also have to be covering ground. The RPMs are lowest at idle, but you're not moving, so it's wasted energy.

SRH

this is exactly true if i keep it under 60 I get about 17-20 mpg once i start climbing up to 70 my mpg goes to ****. at 75-80 i average about 11-12 mpg with 3.55 gears and 35s on with cruise control on.

BolletuH

Putting it in neutral and pushing it.