aliass24

In order to get 3.73's with the 3.5 you have to get the HD payload package.

Great white

iTrader: (1)

You're getting "whammied" from a couple different angles here:

Increase rolling resistance
Heavier tires
Increased wind resistance (drag) from both lifting the truck (underbody is the worst part of a vehicle for drag) and showing more tire to frontal area.
Bigger tires (and probably higher offset rims) are defeating Ford's sneaky little "wind curtain" in the wheel wells
Gearing
Probably have more foot in it everywhere, even if you don't realize it.

It all conspires to give you the 4-odd mpg drop.

About the only ones you can do anything about is gearing and your foot, unless you want to alter the vehicle from its current state.

zx12-iowa

Yes your drop in mpg is normal. I hope your need for extra ground clearance off road out weighs the inefficiency.

WarSurfer

Something you hear over and over on this forum is how you don't need to regear with the ecoboost - because torks

Completely false.

Gearing has NOTHING to do with engine output. Two simple points to prove that out.

1) gear calculators don't use engine output as part of their equation

2) Trophy trucks run over 800hp/700tq and they use the same gearing strategy as us mortals.

Baseline for 35" tires with our 6spd transmission is 4.10:1 - regardless of which engine you have.

Baseline for 37" tires with our 6spd transmission is 4.56:1 - regardless of which engine you have.

Having the appropriate gear will net better mpgs than running oversize tires on too tall of a gear.

Will you get Factory mpg, of course not. Does it make up the cost in a reasonable timespan - irrelevant.

It's about mechanical advantage and reducing premature wear. Do a lot of guys run oversize tires on ridiculously under-geared setups, yep.

As with anything there is the right way to do things and then there is the way everyone else does it. Changing gears isn't cheap but the performance gain far outweighs the cost.

aliass24

What kind of gearing do you think you need with 35's and the new 10 speed?

alping45

iTrader: (1)

My '15 XLT s-crew 3.5 EB w the 3.55 gears was getting 18-19mpg stock. After 2.5 level, +1" spacer in the rear, and 35" STT Pro's, I now average 15 if I'm lucky. And that is running the 5* 91 performance tune with ethanol free 91 octane. With 10% 91 I'm more like 14mpg. Right on par or even a tad better then my similarly configured '13 5.0, but way way more power. I'm perfectly satisfied.

Also the biggest factor I've noticed on mpgs is speed. I run about 30 miles of highway everyday at 75mph, and that is what is suckling down the gas. It's in boost the whole time. If I take a different route on back roads doing 55mph, I can easily gain a couple mpgs back.

WarSurfer

I don't know the gearing in the 10spd but the new Raptor has a 10spd and still comes with 34.5" tires and 4.10:1 gears. That leads me to believe the same rules still apply.

kimber76

I have a 2015 with a 3.5 ecoboost with a 6 inch lift and 35s, I get around 15 mpg which I'm more than happy with. I still makes me scratch my head every time someone posts on here that the mpg sucks. I didn't buy my truck for mpg and I didn't lift it for better mpg. These are trucks they are heavy they are not going to get great mpg. And just for comparison if you Think 14 mpg or what ever sucks with 35s I recently had a loaner from ford while mine was in the shop. They gave me a 2016 f150 with the 2.7 I put 300 or so miles on this while I had it and the best I could get out of it was 14.5. The 2.7 did not impress me at all, For more than just the lack of mpg. Sure it wasn't broke in yet but none the less I will be keeping my 3.5 ecoboost.

ride_002000

Could try a tuner, should gain ~1 mpg or more depending.

D0T-C0M

65-70mph isn't really highway. The speed at which they quote highway speeds is 77km/hr (50mph). I can get about 15-16 mpg with mixed driving too but I'm really babying it. If I rode with a heavier foot 14mpg is pretty normal but I would expect the 3.5L to be slightly better than the 5.0L. BTW, If I drive 45-50mph I get 18.5mpg on the highway.

All values above using the US gal(3.8L/gallon)