I have a 2005 F-150 STX single cab with the 4.2L in it. About two months ago i put a fabtech 6" kit on it and some 35's. I need to swap out my gears but i dont know which ones to get. I might eventually add a 3" body lift and get some 37's so might plan ahead for that. Any help would be great!

 

4.56's or 4.88's.

 

4.10s will be A.O.K too.

 

4.10's may not be low enough with 37's.

 

I agree. If I had a 4.2L I would run no higher than 4.56s with 35s, and definitely not with 37s. I'd say 4.88s.

 

Auto or 5-speed? If it's an auto, 4.56's would do the trick but you'd better watch those tranny temps. Installing a tranny cooler would extend the life of the transmission now having to turn those huge tires.

 

True. 4.10's would be decent for 35's while being modest on the gas.

 

how much would a tranny cooler run me?

 

You can get a pretty nice one on Ebay for $60 if you spend a little time looking.

 

You can easily determine the closest gear that will give you the same final drive ratio as stock by using a simple formula;
new tire diameter divided by original tire diameter times current gear ratio.

example

35/32(=1.09375)*3.73=4.0796

This tells you that you would need a 4.08:1 gear ratio to keep the same final drive ratio you had on your stock tires. Obviously they don't make that ratio, but a 4.10:1 is pretty damn close.

Use it as a guide, if you want a lil more grunt then go up to the next ratio.

 

Was his stock tire size really 32s?

 

I guess if you know your getting the 37's for sure wait for the 4.88s otherwise go with 4.56's. Pat has 4.56's with his 38's so I guess if you decide later to go bigger you'll at least be geared

 

No idea, it was just an example. Obviously you should put your own numbers in the right spots.