Which rear end gearing on new F350 with 6.7 and 10 speed trans

[powerscol]

I am looking at getting a 2020 F350 SRW probably after the first of the year. I want to drive one first. My current 2004 F350 dully king ranch withe 6.0 makes 325 HP and 560 Ft-Lbs of torque. I am running 4:10 LS gearing in the rear end, Trans is the 6 speed. It pulls my 220RK fine and my previous 12K trailer OK before. Could use a bit more power on steep grades for towing both. It is OK with my 26' goose neck loaded with my tractor, etc. Roughly 14 to 16K , but slow. You really know its back there and takes a while to get to speed. Fuel mileage - 14-16 solo and 10-12 towing.

Now the 2020 6.7 is producing 475 HP and 1050 FT-Lbs or torque and has the new 10 speed behind it, Gearing on the 10 speed seems to be secrete, except the top 3 gears are OD.
Rear end has two gears available for 2020 with the 6.7 SRW. Either 3.31 or 3.55. Looking down the road I will probably stay on the smaller 5er side, but for this post assume 12K max on trailer.

So for mountain towing and keeping up with and for folks (not impeding traffic) do I go with the 3.31 or go with the 3.55 which is where I am leaning as it would put less tress on things and have better gearing for down grade control. Solo MPG is important, but I am not finding much information on the expected differences.

What ever happened to the towing guides where you input your trailer and it gave recommendations on how to equip.

Hopefully there is an informed gear head that can enlighten this engineer.

Thanks

[CoChris]

.... Now the 2020 6.7 is producing 475 HP and 1050 FT-Lbs or torque and has the new 10 speed behind it, Gearing on the 10 speed seems to be secrete, except the top 3 gears are OD....

Thanks

Google is your friend


This is from Ford

So in the 10 speed, first is lower and top is taller then the 6 speed.

Chris

[powerscol]

Google is your friend


This is from Ford

So in the 10 speed, first is lower and top is taller then the 6 speed.

Chris

Chris - Thanks

[Jerryr]

I’ve had both 3.31 and 3.55 with 18” wheels on a 6.7L 2017 and 2019. There’s very little difference. At 65 mph there’s 100 rpm difference, 1500 vs 1600 rpm.

If I were to order a 2020 I’d order it with the 3.55. Prior to 2020 in order to get a 3.55 with 18” wheels required HD front springs that degraded the ride when unloaded. Now for model year 2020 you can order 3.55 with standard front springs.

[D2Reid]

If you tow a lot I would lean toward the 3:55. We have a big ol Momentum that weigh's in right around 20k, I went with the F450 primarily because of the towing capacity, second for 4:30 rear end, and third for turning radius.

We play in the mountains a lot.

[Buckskin]

Have Tundra with 4.30 rear end and it will out tow most other half ton trucks due to low ratio of rear end but gas mileage suffers. Would rather have better towing than gas mileage when pulling camper; make great difference when pulling up 7% grade in mountains.

[BubbaChris]

I haven't looked at the details on the 2020 units yet, but my dealer orders all his 2019 F350's with 3.55 so he get the GVWR rating that his customers want/need. I think you'll be cheating yourself out of capacity if trying to save a few RPMs going down the road.

Best regards,
Chris