I have a 2021 F-250 Platinum FX4 with the 6.2, 6r100 and 3.73s on 295/70r18 (34.3") tires w/ Tremor wheels. I also have a 5 star tune on the truck, currently 87 daily/tow. We live in Colorado at 6,400' and regularly tow between 6k and 14k lbs between a gooseneck horse trailer and our dump trailer. It does OK on flat ground with 6th gear locked out but I could use a bit more gear when climbing. The gap between 1-2 and 2-3 in the mountains feels pretty big. While a new set of gears won't change the transmission ratios, it will make each gear lower which is what I want.

The "easy" option here is to pick up a 10 speed truck with a 7.3 but we got this truck for a great deal second hand and I really like the platform. I'm looking at re-gearing the truck and going with a 4.30 or 4.56 gear.

When reading through various posts on this forum, 4.30 gears come highly recommended when ordering from the factory. Unfortunately, my time machine is broken. The F-250 could be had with a ~31.6" or ~34.3" tire from the factory with either 3.73 or 4.30 gears. With the taller tire, a 4.56 gear gets me near the same effective ratio as the smaller tire with 4.30 gears.

If I go with the 4.56 gears with a 6r100, this gets me the same close to the same first gear ratio as the 10r140 with 4.30 gears as well. Also, 4.56 gears effectively makes the 6r100 6th gear what I have with 5th gear and 3.73s today which is how I tow on the highway anyway with 6th locked out. With 4.56 gears, in 6th gear my highway cruising RPM would be ~2,300 RPM @75 MPH.

If I'm going through the cost of re-gearing at around $3,300, go big with 4.56 gears vs 4.30, right?

Comparison of 3.73 vs 4.56:




Comparison of 4.30 vs 4.56:




Here is the comparison between the 6r100 and 10r140 transmissions with various final drive ratios. The 6r100 w/ 4.56 and 10r140 w/ 3.73 are fairly similar except for the OD gears:




This is a typical weekend of hauling stuff for the farm:

4.5 Tons of gravel

122 small bales

 

I would go deep with the 4.56 gears. Gassers that tow heavy really benefit from deeper gears.

 

If you're working your truck like it seems you are, I would even look at stepping to 4.88's, the smaller engines need all the help they can get...

I have a 00 Ex with the 5.4 and 35's, went from the stock 3.73's to 4.88's, then to 5.13's (had d/s issue so had to rplc gear-set) almost wish I would've gone to 5.38's since we also live in the mtns, and are either going uphill or downhill.

 

4.56 and mid grade gas when towing. Great combo because the 6.2 lasts forever.

I ran the 5star 87 octane tune and 89 octane gas around town and when towing. Could tell a difference for sure in the 6.2.

If you get into the gears see about adding a front locker.

 

I had the exact same set up as yours except for the tune. Same engine, transmission and tire size but with the 4.30 gears. Spent a lot of time in the New Mexico mountains with truck camper in high altitude.

I would get at least the 4.56 if you are doing some interstate driving,

 

I am looking to the same thing and I am wondering what gears others have used? Are there Ford OEM in 4.56 or would it have been Nitro or Yukon?

 

This is great feedback. When you say at least 4.56, would you also think about 4.88? I definitely see the benefits, but I'm not sure if I want to be turning more than 2,500 if we are unloaded at 75-80.

 

My situation was a different truck (Excursion). Different engine (6.8 V-10). Different transmission (4R100 4 speed auto). Larger 305/70R18 (35”x12.8”) vs stock 265/75R16.
My big wagon came with 31.6” tires and 3.73 gears and it was a dog towing our old 9500lb toyhauler. I wanted to run those taller tires so I upgraded to 4.88 gears for a season before I bought the tires and with the 31.6” tires and 4.88s it towed like a locomotive! Later with the bigger tires and 4.88s (effective ratio of 4.39) it still pulled great with hardly any downshifting on the highway. Then we upgraded to a 41’ 3 slide TT that scaled at 12K lbs and the tire / gear combo continued to deliver very good towing performance, logged about 75K towing miles with that final setup with it never feeling under powered. I’m based here in the East and highway speeds in the Mid-Atlantic region typically are bit lower than out West, my typical highway cruising speed was 65 MPH where it turned 2430 RPMs, 70 MPH was 2600 RPMs, which may seem kind of high but in reality the motor liked it, higher revs but less actual load due to the steep gears.
Dont fear the gear!
That Excursion was a dedicated tow rig that did not see any daily driving duties, it’s unloaded miles were all touring around our travel destinations.

 

I would not hesitate to go with the 4.88's, buy once, cry once, and after having a Tru-trac installed in my Ex, I would highly recommend one since you're going to be in there, and if it's revving too much at 75... slow down a tad I know, I know, the speed limit is 80, but that doesn't mean you have to go fast... I have found in almost all my trucks, from old 1966 F100, to my '02 F350 and my '22 F550 work truck, as soon as I cross the 65-67 threshold, mileage starts dropping. In my '00 Ex w/5.13's/35's on our last trip to TX I experimented along the way between fill-ups, 65-67mph tanks returned the best at almost 19 mpg in the the big pig Dory, running 70 dropped her to 14-15-ish, pop over 75, dismal, was 11-12. Did pretty much the same thing in my '02 F350/DRW/7.3/4x on the trip in 2022, 4.10's w/35's, 65-67 was the best return in mpg.

Personally, I'd rather have the grunt for work and towing and go a bit slower on the hwy, and the change from 4.56 to 4.88's in reality is negligible, but when it's gets down n dirty and heavy, it makes a difference.

 

How much time do you spend at 75-80mph? If it’s less than 50%, I’d look at the 4.88’s.

 

This. 4.56 or deeper and don't look back.

 

Regularly tow = 4.88.

Gears are expensive. Go big, so you feel the difference. Put a Yukon Grizzley locker in the front axle at the same time.

 

I think you guys talked me into 4.88s. I did some unloaded highway runs between 70-75 in 4th gear running around 2450 rpm. Truck felt comfortable and I was able to get 14.6 on my first run and 15 on the next:


First run

Second run

 

My 550 has 4.88 and wee lil tires. And its diesel.

Its fine. A gas engine, that likes more revs, will be in heaven. Dont forget to upgrade the front diff while in there.

 

What do folks recommend for upgrading the front diff?