88 F150 4.9L 4x4. Pitting a 6” Lift on, and will have in the future 35” tires. This is my business truck that I use to haul things, heavy equipment. What is the gearing recommendation??

 

4.10 for sure.

 

Agree with 4.10s, the numbers suggest that 4.56s wouldn't be out of the question if the gearset fits the axle, as you'll be pushing a bigger brick wall aerodynamic against the wind.

 

Just out of curiosity I compared tires sizes to gear ratios as a percentage.

Tire size in inches seems to increase ~6% from stock (29"?) through 35", and people's recommended gear ratios seem to fall pretty close.

Tire sizes: 29---31---33---35

Using 6%: 3.55-3.76-3.98-4.22

If you're planning to tow, you may want to go straight to 4.56, but 4.10's might be slightly better for highway fuel economy.

From what I've read (also planning for 35's in the future), you may need a different carrier for the front diff if going above 3.92?

 

Ok, I appriciate it. I was towing a lift the other day and trying to go from stop to start just took a lot of effort to get out of Gear.. than when reversing trying to get it in place I was smoking bad!

 

I hope you are planning on trailer brakes. We used to haul a very heavy pickup bed trailer about 30 miles every month or so, with my 4.9 '87 4sp short bed. Even with 3.08 gears it was doable if you weren't in a hurry to get to 60 mph, but needing to plan your stops was an understatement. It would push you right through a stop if you weren't careful. I had no control over the weight, as others were loading it, but I'd estimate it was well over 2 tons. It is fairly flat and level here, in hill country that combo would have more serious consequences. I've grown up a bit since then, don't think I'd even attempt that now.

 

Something I noticed while driving, I was going through construction speed limit 55 I was going a little slower, than normal and had my cruise control on and when I passed a speed radar, my cruise was set to just below 50 and it said 56? Could this be because of 33” tires and lower gears?

 

Yes.
Your speedo should be cable driven off the back of the tranny. You'll have to do some calculating to figure out which little gear you need for the speedo cable to put it back in sync.