I have a 99 f250 with some procomp (325s) that are 12.5 wide with a 6in lift my superchip tuner can change the trannys shift points but im pretty sure a new gear ratio is needed. I dont do a whole lot of off roading with it its mainly my driving around and highway rig whats a good gear ratio that would work for me

 

Which engine do you have? That does play a factor.
If the v10 or a 5.4 a lot of members have raved about the v10 with 4.30 combo. With your size tire equivalent would be at least a 4.56 or 4.88, those gears will also be good for towing.

If you have a 7.3 diesel probably not going to want much more than a 4.10 as you would be spinning high RPMs otherwise.

 

its the 5.4, and i dont tow or haul with it

 

Then the minimum you would want is 4:88..

 

It's hard to say, based on the lack of information, but you can figure it out yourself.

Say your old tires were 32 inches tall and your new tires are 34 inches tall. Also lets say your truck has 3.73 gears. You plug these values into the Automotive Calculators offer to you by Ford Trucks Enthusiasts | www.ford-trucks.com calculator and it tells you that you need a 3.963125 gear ratio to return the truck to the stock effective ratio.

 

i had 35x12.50's on my '99 5.4 and with factory 4.10's it still needed more gear to really get moving and hold a gear on the freeway.

 

no towing at all i say 4.56 should get you the low end power back and still be able to have good highway mpg without screaming the motor BUT if you plan to go larger tire or tow anything more than a small fishing boat or aluminum boat go 4.88 gears

 

im running a 2004 5.4 in my sig with 4.30 gears and pizza cutter 255/85r16 tires roughly 34" tall and my truck is perfect the way it sits for now...... a buddy has a 2003 f250 same body style as mine but 4.10 gears running 315/75r16 goodyear duratrax tires and he does offroad his truck and in 4high the motor sounds like its barely able to run let alone turn those four 35" tires. This is why my buddy uses 4low all the time. Now he does own a 20ft carolina skiff with 130hp evinrude and tows it all over New Jersey for fishing and he says he gets 14mpg but i know hes lieing. i want 35's on my 04 but im not re-gearing the truck again so im not going any larger than a 255 or 285 tire like i have now

 

Well im not runnin pizza cutters lol they are 325 procomps that are like 12.5 width sooo would a 4:29 still work?

 

325 is the width, which says nothing about the overall diameter of the tire without the rest of the measurements. Width is inconsequential. What really matters is overall diameter.