Okay, so I'm going to be buying a gear kit soon to regear my differentials. Since I'm going to be running 37 inch tires, what ratio is best to work with? I ask because some say too high of a gear and the rpms will be high when cruising down the road at highway speeds. I thought of a 4.88 with 37s. Truck will have a programmer to adjust the gear size and tire size. What will work best for being as close to stock ratio with the 37s? Thanks

 

If you want close to stock and no performance gain I think 4.56 is closer for 37s. There are charts out there but beware they aren't 100% accurate for every application unless you find an F150 specific gear to tire-size chart

 

What's your ratio now?
Or your axle code?
The formula is easy
New tire size multiplied by current gear ratio divided by current tire size

Example;
37x3.55÷30=4.37
So a 4.56 would be really close to stock
If you're towing or wheeling I'd go 4.88

 

He has the ecoboost and most likely 3.55 gears at best since it is a platinum and the most popular gears.

 

4.56 would probably be the best all Around gear to go with and would still work real well if you went down to 35s. However 4.88s would definitely be a good gear ratio if your planing on towing or actually using the rig as a off road machine.

 

I'm not doing any offroading actually, going to be driven only on the road lol.

 

That's a real shame...

 

4.56 would be the best choice.

 

4.56 does seem right , to be back to stock. but remember those tires are way heavier than stock and need more gear to get moving . my choice would be 4.88.

 

4.56 to 4.88 is not a huge difference your probably talking about 100rpm difference at 65mph.

Here is a comparison on your set up with 37s and the ford 6R80. Left side is 4.56/ right side is 4.88