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Towing with 3.31 vs 3.55 (Diesel)

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Towing with 3.31 vs 3.55 (Diesel)

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Old 07-18-2018, 10:18 PM
Flyct
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Towing with 3.31 vs 3.55 (Diesel)

My current F350 diesel has a 3.55 ELock rear. I just ordered a 2019 with a 3.31 ELock.

The 3.55 requires HD front suspension which I wanted to avoid.

I tow a 14000 lb 5th wheel. The 3.55 seems to run RPMs up pretty high and hold onto lower gears pretty long with light/normal acceleration in tow mode when towing.

Any thoughts on the two rear ends for towing this load with the diesel?

JR
 
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Old 07-18-2018, 10:27 PM
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Lower gear ratios are for towing (higher numerically), higher gear ratios are for better fuel mileage and less power. A 14K lb 5th wheel is not light and you need all the gearing you can get. You are replacing your truck with a less capable one.
 
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Old 07-18-2018, 10:55 PM
Maximus216
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it just seems like a no brainer to me to go with the lower gear ratio to tow. if ford offered a lower ratio than 3.55 i would have got it. the difference between 3.31 and 3.55 in fuel savings is probably minimal.
 
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Old 07-18-2018, 10:55 PM
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For both 3.31 and 3.55 the Ford tow guide shows same 5th Wheel Max tow weight of 20,700 lbs. My Andersen Ultimate Hitch is rated for 24,000 GTWR and 4,500 lbs pin weight. So by specs I shouldn’t have a problem. Looking for real life experience.

Anyone towing 13000-14000 lbs with a 3.31 diesel care to reply with their experience?

My 3.55 tows this load effortlessly. The 6.7L Diesel is a torque monster.
 
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Old 07-18-2018, 11:14 PM
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Depends on the wheels/tires. Less than 3% difference between 18" with 3.31, and 20" 20" with 3:55
 

Last edited by labrown; 07-18-2018 at 11:16 PM. Reason: formatting
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Old 07-18-2018, 11:15 PM
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Originally Posted by Flyct View Post
For both 3.31 and 3.55 the Ford tow guide shows same 5th Wheel Max tow weight of 20,700 lbs. My Andersen Ultimate Hitch is rated for 24,000 GTWR and 4,500 lbs pin weight. So by specs I shouldn’t have a problem. Looking for real life experience.

Anyone towing 13000-1400 lbs with a 3.31 diesel care to reply with their experience?

My 3.55 tows this load effortlessly. The 6.7L Diesel is a torque monster.
this has been beat up on other threads ten ways to Sunday. Correct, the Ford tow guide rates them the same. Note that the tire size is difference, so I believe I read that the final drive ratio is the same for both rear ends with the stock tires, the 3.55 with 20's and the 3.31 with 18s. All of that said, after testing driving only vehicles with 20s on it, I took a chance on the 18s and glad I did. Ride is great and it tows effortlessly. I am only pulling 8k conventional, so I can't answer to your weight. But there are other threads about it on this forum. Search 3.31 and 5th wheel and you should find it.
 
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Old 07-18-2018, 11:17 PM
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My Lariat Ultimate diesel is a 3.55. I just finished a 2800 Km trip towing my 8000 lb TT. We were fully loaded, at max GVW of trailer, resting on the overloads on the rear axle, had the bed of truck loaded as well. But probably not touching the limits of the truck GVW, and at about 18,000 lb GCW. I towed on prairie, and western hills, and in lots of heat. Towing at 60-65 mph, 6 th gear all the time. Towing at 70-75mph, and with headwinds, even with my lighter load, shifting into 5th on hills, and fighting cross winds and wind direct on. I would say in a 3.31,with your trailer, you will be shifting down again (4th) with a 3.31. For note, I have currently got the stock tire size and they are below 40% tread. If I were to upgrade to larger tires, I would end up down to the 3.31 range.

my advice is to change to 3.55 when you order. I am assuming a 14,000 GVW trailer will be a fifth wheel and frontal area will be a significantly higher drain on power especially in wind. I am thinking that your towing experience will be far better with the lower gears, higher 3.55 ratio. That being said, I went from a 4.10 F350 gas, a 4.10 Mustang 5.0, a 3.73 F350 6.0 diesel.
 
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Old 07-18-2018, 11:29 PM
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Ordered the truck with 18” wheels as I have on my 2017 F350.

I have about 18000 miles on the current truck with about 9000 of those miles towing the 14000 lb 5th wheel.

I keep speed max at 65 MPH and I can only remember maybe 2 times it downshifted from 6th to 5th gear going up some hills.

My previous 2016 F150XLT with 3.5L EB was always downshifting towing 7500 lb bumper pull trailer.

Heres a screen snapshot of my 2017 w/3.55. At 65 MPH RPM is only 1650 RPM.






 
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Old 07-19-2018, 04:58 AM
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Originally Posted by Maximus216 View Post
it just seems like a no brainer to me to go with the lower gear ratio to tow. if ford offered a lower ratio than 3.55 i would have got it. the difference between 3.31 and 3.55 in fuel savings is probably minimal.
This line of thought comes up just about every time the debate over gear ratios does. "Get the lower gear ratio, the fuel savings is minimal", conversely that reads get the more fuel efficient ratio, the extra torque multiplication is minimal.

My truck gets driven much more often 'unloaded', I opted for the fuel savings.
 
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Old 07-19-2018, 06:28 AM
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My understanding of the 2019 Order Guide (page 10) is that you can order the 3.55 EL on a 4x4 with 17” or 18” wheels with the optional camper package. The maximum +1 up on the front springs probably wouldn’t be noticeable.

HTH,
Jim / crewzer
 
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Old 07-19-2018, 07:46 AM
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Originally Posted by Flyct View Post
Ordered the truck with 18” wheels as I have on my 2017 F350.

I have about 18000 miles on the current truck with about 9000 of those miles towing the 14000 lb 5th wheel.

I keep speed max at 65 MPH and I can only remember maybe 2 times it downshifted from 6th to 5th gear going up some hills.

My previous 2016 F150XLT with 3.5L EB was always downshifting towing 7500 lb bumper pull trailer.

Heres a screen snapshot of my 2017 w/3.55. At 65 MPH RPM is only 1650 RPM.






Wow. I'm impressed by your mpg number. I have exactly the same truck and RV model and I get around 8 mpg towing and 13 mpg around town. I have the 20" wheels with 3.55 rear end.
 
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Old 07-19-2018, 07:50 AM
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I pull about 14K with the 3.31 with no issues. When I encounter a long hill, I lock out 6th, no problem.
 
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Old 07-19-2018, 07:54 AM
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I tow a 24' car hauler, loaded weight about 9K lbs. My truck pulls this load effortlessly. It could easily use the 3.31. If I had it to do over I would get the 3.31 instead of the 3.55.
 
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Old 07-19-2018, 07:56 AM
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My 2014 has 3.31's and we upgraded to a 38 ft toy hauler this year with an empty weight of 12500 and with the sxs, water, fuel, kids, and crap I'm sure we are pushing 17000. I tow all over Western Montana and I cannot wait to get my 2019 ordered to get 3.55's. the 3.31's will do it but it shifts for every little rise and allot of the mountain passes we are crawling up in 3rd gear. My truck is not my daily driver and I only have 37k on it so I guess you got to ask yourself what is more important, empty fuel economy or towing capability. Personally I would change your order, especially if you tow in any mountains regularly.

Good luck!
 
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Old 07-19-2018, 08:02 AM
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Originally Posted by SouthTXfiver View Post
Wow. I'm impressed by your mpg number. I have exactly the same truck and RV model and I get around 8 mpg towing and 13 mpg around town. I have the 20" wheels with 3.55 rear end.

I’m very happy with the MPG. 18” wheels with 3.55 rear. I replaced the Wrangler tires with Michelin Defenders. I keep tire pressure at standard 60 psi front and 80 psi rear. I also have a BakFlip F1 bed cover that I believes helps reduce parasitic drag.

Towing cuts the MPG in half, or about 10-11 MPG

Not towing at 65 MPH routinely we show 20-21 MPH. I goes down to about 18 MPG at 75 MPH.
 
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