Originally Posted by petespatio
I am getting a newer F150 to pull this travel trailer.
3.5 eco boost.
I see gear ratios of 3.55 and 3.73.
What would be the recommendation?
Depends on the year. 6 speed, 3.73, 10 speed 3.55. If you plan to drive it more than just when towing, the 3.55 will be better overall since the 3.5 doesn't need to rev high like the 5.0 to hit the power band, which is what the shorter gears give you.
If you look at the Max Tow package Ford offers with the 3.5 EB, the ratio is 3.55 as that one works best for both MPG when empty and power when towing. I have an 18 with Max Tow. Pulls my Coleman around effortlessly and would not want the shorter gears since it is also my daily driver, and fuel economy is important as well. I get 20-22 MPG in it when driving to-from work every day.
With the 10 speed, the lower gears with the 3.31 rear end are equal or very close to the 6 speed with 3.73 gears. The 3.55 are better than the 3.73 with the 10 speed vs 6 speed. Also since the EB produces the torque way down low starting at 1500, the pairing works very well for that engine. If it were the 5.0 where the torque is near 3K before it pours it on, then 3.73 is a must since you want the engine to rev up that high quickly.
Hope that helps some. You also will find 3.55 much easier on the lots than 3.73.