Re: diff gear ratio\'s
>>>The only difference going from 3.08, instead of 3.55, to a 4.56 ratio is that your speedometer will be a little further off. You will read about 72 miles an hour when your going an actual 65(35s). 3.55s to 4.56 would have left you almost exact with 35s. The 39s may make the actual speed a little closer to the speedometer. You may be able to change the gear that goes in the tranny to accomodate any difference in speed. You'll have to check with Ford to find out for sure though. I had 3.55s and put in 4.56s with 36 inch tires and the speedometer was within 1 mile an hour at 65 so I left it alone. I was fortunate enough to have a friend with a GPS and he was able to check our actual landspeed from inside the truck and compare it too my speedometer. By the way, do you have a 5.0 or 5.8? The reason I ask is due to the weight of a Swamper compared to anything 35x12.5 that is radial. If you have the 5.0 you may want to stop at 36 inches unless you are going to do some perf mods to the motor. If you have a local 4x shop with display tires go on in and lift a few and you will see what I mean. If, when I put my 36 inch Swampers on, I had known they would weigh so much more than my buddies 35x12.5 BFGs I would have went one gear deeper to accomodate the rolling weight resistance they have. P.S. Don't forget harder to move means harder to stop-might want to look into a rear disk set up for all that rubber. I'm done now. Later.