3.31 or 3.55 with 10 speed transmission
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Fleet Mechanic
Joined: Oct 2006
Posts: 1,351
Likes: 242
From: North Florida
3.31 or 3.55 with 10 speed transmission
Does anyone have experience towing moderately heavy loads with the 10 speed transmission and 3.31 gears? My current truck has 3.55 gears with the 6 speed. I’m considering ordering a new truck and wonder if I should stick with the 3.55 or go 3.31. My 5th wheel is around 14k pounds. A friend of mine has a 2021 with 3.31 gears that he claims tows 15k pounds like a beast and gets great unloaded mileage.
Post Fiend
Joined: Nov 2001
Posts: 6,748
Likes: 118
From: Tallassee, ALabama
I would go with the 3.55 gears since you are towing. You would not see much difference in fuel mileage when not towing. The 3.31 would be a tad sluggish when towing but the 6.7 is a beast and could tow your rig with no problems. Go read Ford's towing guide to see what your max load would be for each gear set.
https://www.fleet.ford.com/towing-guides/
2021 towing guide....
https://www.fleet.ford.com/content/d...owingGuide.pdf
https://www.fleet.ford.com/towing-guides/
2021 towing guide....
https://www.fleet.ford.com/content/d...owingGuide.pdf
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
Having both trucks to drive I can say the 3.31 builds boost and holds it better. The 3.55 is fine but keeps the Powerband up slightly. Overall it's such a slight difference, the 3.31 does for sure net over 21mpg unloaded. Ford rates them both to tow the same.
Lead Driver
Joined: Nov 2005
Posts: 5,222
Likes: 4,232
From: Kaysville Utah
What size tires do you want to run? Most 3.31 run the smaller tire. If you plan to plus size the tire. Maybe to full 35" tire. Id stay with the 3.55.
I'm towing a 13,000 lbs GN horse trailer and getting 11-12 mpg. Which is about 1 mpg better than my 2017 Truck with the speed did.
I did one mileage run where I really babied the truck to see what the best possible I could get. Went 140 miles @ 70 mph and got 22 mpg. No stop, no start, no passing, Just a constant 70 mph I'm seeing mileage in the 18 mg for most empty hiway driving and 14 for my daily driver
I am leveled, running LT295/65R20 tires
I'm towing a 13,000 lbs GN horse trailer and getting 11-12 mpg. Which is about 1 mpg better than my 2017 Truck with the speed did.
I did one mileage run where I really babied the truck to see what the best possible I could get. Went 140 miles @ 70 mph and got 22 mpg. No stop, no start, no passing, Just a constant 70 mph I'm seeing mileage in the 18 mg for most empty hiway driving and 14 for my daily driver
I am leveled, running LT295/65R20 tires
Thread Starter
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Fleet Mechanic
Joined: Oct 2006
Posts: 1,351
Likes: 242
From: North Florida
What size tires do you want to run? Most 3.31 run the smaller tire. If you plan to plus size the tire. Maybe to full 35" tire. Id stay with the 3.55.
I'm towing a 13,000 lbs GN horse trailer and getting 11-12 mpg. Which is about 1 mpg better than my 2017 Truck with the speed did.
I did one mileage run where I really babied the truck to see what the best possible I could get. Went 140 miles @ 70 mph and got 22 mpg. No stop, no start, no passing, Just a constant 70 mph I'm seeing mileage in the 18 mg for most empty hiway driving and 14 for my daily driver
I am leveled, running LT295/65R20 tires
I'm towing a 13,000 lbs GN horse trailer and getting 11-12 mpg. Which is about 1 mpg better than my 2017 Truck with the speed did.
I did one mileage run where I really babied the truck to see what the best possible I could get. Went 140 miles @ 70 mph and got 22 mpg. No stop, no start, no passing, Just a constant 70 mph I'm seeing mileage in the 18 mg for most empty hiway driving and 14 for my daily driver
I am leveled, running LT295/65R20 tires
Posting Guru
Joined: Aug 2007
Posts: 1,902
Likes: 26
From: BA, OK
Does anyone have experience towing moderately heavy loads with the 10 speed transmission and 3.31 gears? My current truck has 3.55 gears with the 6 speed. I’m considering ordering a new truck and wonder if I should stick with the 3.55 or go 3.31. My 5th wheel is around 14k pounds. A friend of mine has a 2021 with 3.31 gears that he claims tows 15k pounds like a beast and gets great unloaded mileage.
3:31 with the 10R140 is equivalent to 3:73's with the 6R140. The 3:31's are more than enough for most that tow only occasionally. If you tow heavy most of the time would be the only reason to go 3:55 which would be equivalent to 4:30's with the 6R140.
Here is a post of the final drive comparisons.
https://www.ford-trucks.com/forums/1...l#post19741193
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Tuned
Joined: Jul 2003
Posts: 274
Likes: 20
I have a 2019 6.7L (lower HP and Torque than current trucks) with the 6-speed and 3.31 rear end. I full time RV with a 15,000 fifth wheel and it tows great. Sure, it will come out of 6th on some climbs, but the truck certainly doesn't need a 3.55. And when not towing it never comes out of sixth and get slightly better mileage with the lower gears. I imagine that the 10-speed would handle the 3.31's even better.
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3.31 gears with the 6.7/ten speed is capable of putting more torque to the rear axle in low gear than 4.30 gears could with the 2019 6.7/6 speed. For trailers under about 18000 lbs the 3.31gears will pull a little better than the 3.55 gears in the hills. 3.31's will give you a little better fuel economy when running empty. So, in my opinion the only reason to even consider 3.55 gears in a new Ford SRW diesel would be if you wanted to tow heavy all the time and run 37" tires. I have 34" tires on my 2021 and find it tows beautifully with 3.31 gears .... under certain conditions I have found it beneficial to lock out 10th gear when towing heavy.
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