Expedition R & P ratio question...

[grantpa]

I have an '00 EB Expy/4.6/2WD the tires that came with the truck are close to 32" tall and my 8.8 has 3.31 gears. Why did Ford use such a high ratio if they're shodding these trucks with that large a tire???? According to most ratio calculators the R & P ratio should be-at a minimum-3.73's, and preferably 4.10's for towing apps. Why the 3.31's? Am I missing something??? My truck feels awful slugglish off the line and the mileage sucks! I'm thinking that a move to 3.73's may help on both fronts. Thoughts?

 

[Bedrck47]

Although the 3.73's will increase your towing capacity they will cause you to be slower off the line and will be a decrease in MPG's

 

[grantpa]

Hey Bedrck, thanx for the reply. I'm curious. It seems a lowering of the ratio to 3.73's vs stock 3.31's would have the opposite effect, quicker off the line and better MPG's because, due to gear compounding, the engine would have to work less hard to achieve the same result. Again, am I missing something? Perhaps the modular engines were deigned to operate in a certain RPM range for a good balance of fuel econ and power? I'm just wondering why Ford would pair a pretty heavy truck and a smallish engine with 3.31's and 32" tires. It defies common practice.

 

[ExplorerTom]

3.73 will definitely make you quicker off the line vs the 3.31.

MPG is tougher to figure out. It depend a lot on the type of driving you do. It'll raise your RPMs for any given speed- but that not necessarily bad. If you stay closer to peak torque you can actually improve MPG.