Hey everyone,
I have a 1997 f350 460 that has 3.55 gears from the factory. When I tow the truck handles the trailer alright but I thought if I had lower gears installed (maybe 4.10s) it would pull a little better and allow me to step up to 33 inch tires. I bought the truck last year and it has only 33k on it now so I plan to keep it for a while. I just don't know a lot about changing the gearing and if it is worth messing with. I am most concerned with the life of the truck. If I have new gears installed am I creating more potential problems than it is worth?

thanks for your help,
Keith

 

The best reason I've come by to change gears is you aren't content with the ones you have. Serious. Changing tire sizes is a close second, since it changes the "effective" gearing at the ground.
Changing gears will cost some dough. That's life. You could lose or gain mileage, depending on what you change to and why. If you're way too low in rpms for a given speed, a gear change could put you back into the place in the power curve you want to be, and mileage could improve. You could make your revs too high and lose as well.
355 seems light for trailering. My diesel came with 373 and that is fine for just trotting down the road but it was lousy for the trailer. 456 is a lot better for the trailer but the mileage didnt get helped.
If you do change, since you are tugging, upgraded diff covers with cooling fins arent just an aesthetic consideration; I think they're worthwhile as peace of mind for keeping the temps polite.
You can look at gear calculators here or virtually any retail online site that sells differential parts. Those can show you anticipated rpms at a given speed and tire size for whatever gear you're considering.

 

At 60mph, with 3.55:1 gears, assuming you are running a stock tire, ( like a 265), your engine rpm's are about 2110, in overdrive (or 5th gear). Same scenario with 4.10:1, engine rpm's increase to 2444.
Now a 33" tire with 4.10:1, @ 60mph (high gear) would make engine rpm's about 2296. That is close to the stock final drive ratio.
The truck will pull better with the little tires, and lower gears, and the bigger tires, with lower gears will be slightly better than what you have currently. Hope this helps.

 

If you aren't happy with it the way it is, putting larger tires will make it worst. Like he said, going a 1/2 rev lower will make a nice change if you do go with the 33", but is probably a little steep with stock tires.

My 79 hada 351m, 4.10's and 36", I never pulled a trailer, but it could do it with ease. 3.73 maybe a better choice, esp if you only want 33"s.