99 f150 4X4 DD build
 

https://s26.postimg.org/ok1ieuw3d/20170917_132526.jpg
This is my new daily driver a 1999 f150 4X4 xlt with a 4.6 titan and 5 speed manual transmission.
I just picked it up 3 weeks ago and so far I've changed the spark plugs and wires, changed the rear diff fluid to mobile 1 75w 90, changed the oil to mobile 1 5w30, converted to electric fan and m3 style mirrors. My current goal is 25 mpgs

Yesterday I replaced the fluids in the front diff transmission and transfer case to mobil 1 synthetic fluids and added a lawn edging air damm and according to my ultragauge it gained 2 mpgs
https://s26.postimg.org/x3phqcttl/20170916_140043.jpg
My next mod will be tires it's currently running on bfgoodrich all-terrain t/a 265/70 R17 but I want to switch to a highway tire with the lowest rr possible

I have always had good luck with Michelin LTX M/S2 or the new LTX Defender on a variety of Chevy and Toyota trucks. I have run LT235/85R16 and P245/75R16 with good success, both producing good traction and good MPG. Provides great traction on road (especially in inclement weather) and fairly good traction offroad (better than you would think) as long as you stay out of deep mud. If you go too wide for the weight of your vehicle you will be more likely to hydroplane and probably won't like the traction. I put 265/70R16 on my Tacoma (from my wifes 4Runner when we got it) as a stop-gap and do not like the traction compared to my LT235/8R16s that used to be on it. Her car now has better traction, getting new 245/75R16s (identical diameter and tread pattern, just different widths).

Do you know the rear end ratio or how many RPM you are at at 55 MPH? One reason to switch to a taller tire is to reduce the RPM for a given speed, but I have found this effect helps less than the lower rolling resistance so don't compromise your tread pattern for the sake of diameter (been there done that with 255/85R16). A good tread pattern in tall and skinny is your friend for good traction and good mpg.

At least that is my experience with five 4x4 vehicles and trial and error with more tires than I can count, I am sure others may have had other experiences.

At 60 I'm running about 1950 rpm but a set of 2.73 gears should get me to around 1400 rpm. I'll have to check if they come in 17"

1950 RPM at 60 MPH is a little better than where my Tacoma is (2000 RPM @ 55MPH w/32" tires). You can find 245/70R17, 245/75R17, and 235/80R17 in Michelin LTX Defender or MS2. Some of those sizes are in LT only, not P rated. Were those lower gears offered for the front differential as well? I know with the Tacomas and Chevys you could get much lower gears for just the rear than you could for the front, thus a 4x4 was somewhat constrained on the lowest ratio available. I have 4.10 in my 1994 4x4 Diesel Suburban project that is ongoing to replace my Tacoma, I plan to swap those to 3.42 which is the lowest ratio I can get for the front.

The mechanic at my job says rear gears should work in the front and if not I'm sure I can just use 3.08 in the front and only use 4wd if I get stuck in mud or snow.

I've been wanting to remove my front axels anyways they're always spinning even when not in 4wd they're bolted through the front hubs like a fwd with no lockers available and I think I can get around just fine in 2wd

https://m.tirerack.com/tires/tires.j...omCompare1=yes thinking about getting these tires but don't know how long winter tires will last driving year round?

I have to ask... what are you hauling around every day?

Well currently nothing its my dd while I'm swapping the motor in my Saturn. I am however working to start a business.