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Thoughts on F-150 Axle Ratios

Knickell

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Does anyone have an opinion on what the best axle ratio is for the 21’ F-150? (3.15, 3.31, 3.55, and 3.73)

Is there any discernible difference between the 3.31 and the 3.55?

Looks like the 3.31 comes with the FX4 package, and the 3.55 come with the Max Tow package.
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Agashi25

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Does anyone have an opinion on what the best axle ratio is for the 21’ F-150? (3.15, 3.31, 3.55, and 3.73)

Is there any discernible difference between the 3.31 and the 3.55?

Looks like the 3.31 comes with the FX4 package, and the 3.55 come with the Max Tow package.

I personally did 3.73 on the lariat 4x4.

From what I understand 3.31 won’t give you as much power when accelerating but will get great MPG. But if you’re towing not so great.

Higher gears will give you more “power” on acceleration but worse MPG under normal driving. But when towing it’s not as bad as towing with 3.31?

This is just from what others have said on f150 forums that I gathered.
 

Roger350

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It all depends what you use your truck for. The differential gearing multiplies torque and changes the rotational speeds and directions. A high numerical ratio like 3.73 or 4.11 (called a lower ratio, low gearing, or short gears) multiplies the engine's torque more than a lower numerical ratio like 3.31 (called a higher ratio, high gearing, or tall gearing).

So more torque is better, so what is the tradeoff? Engine RPM and fuel mileage. Those 3.73 or 4.11 gears will require the engine to turn much higher RPM for a given vehicle road speed than the 3.31 gear set will. So at 70 mph on the highway you might be turning 2800 RPM with that 3.73 versus 2200 RPM with the 3.31 gears. And with increased engine RPM comes increased fuel burn, so worse fuel mileage. Engine and drivetrain wear may also increase with those higher sustained engine speeds, but that would be hard to prove.

There is no one size fits all gear ratio. The 3.55 is the middle of the pack, and is probably a reasonable compromise, but Ford's engineers have chosen which ratios you can get with which engine, and have specified their towing and payload ratings based on those drivetrain combinations.

Match what you plan to use the truck for with those ratings, and you'll have the gear ratio the engineers believe is best.

Personally, I wish I could have gotten the 3.55 with the PB 4x4, but that combination forces the 3.73 ratio. I know I will not be towing very often, so I'd rather trade a little towing grunt for better fule mileage,. But Ford was designing to a max trailer rating so they decided I cannot have a 3.55 with that truck because it's too heavy, and they think it needs more torque multiplication.
 
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Since the F-150 does have a 10 speed transmission I would prefer a more agressive gearing(3.73:1). I think there should be an option for an even more agressive gearing with the 3.3 something like a 4.10:1.
 

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Since the F-150 does have a 10 speed transmission I would prefer a more agressive gearing(3.73:1). I think there should be an option for an even more agressive gearing with the 3.3 something like a 4.10:1.
I'd like to know why with 10 speed transmissions, 10th gear isn't a taller overdrive than 0.636. Eighth, ninth, and tenth gear are all overdrives, why not have tenth closer to 0.50? I'm sure there is a logical explanation, and it likely has to do with diminishing returns and efficiency losses with such a tall overdrive, but if it was closer to 0.5 then the rear end ratios could offer the best of both worlds, making the 3.73 a better compromise for towing power and fuel efficiency. Surely they could lock out tenth gear in tow-haul mode, or something along those lines.
 

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Posted this a while back over on the other forum, but ... regarding the Powerboost 4x4 only being available with the 3.73 instead of the 3.55 differential, remember that the new(ish) 10 speed final (over)drive is 0.63 vs. the old 6 speed which had a 0.69, so multiplying that out, the RPM in top gear would actually be 4% lower for anyone from an F150 with the old 6 speed .... that is if I've got my math right!

Sticking with the theme, first gear in new truck with 10 speed would be 4.69 vs 4.17 in the old 6 speed. For first gear matched with 3.73 vs. old 3.55 differential that would be 18% more stump/trailer pulling force off the line
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So, anyone coming from an older F150 with 3.55 the new F150 with 3.73 and the new(ish) 10 speed, first gear is 18% higher and top gear 4% lower. The best of both worlds, at least compared with my old 2016 F150!
 

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I had a 2004 4x2 Lincoln Navigator with a DOHC 5.4L, 4 spd auto, 3.73 gears. I would get 17 mpg highway at best.

I changed to a 2011 F150 4x2 King Ranch with 1st gen 5.0L, 6 spd auto, 3.55 gears. I would get 21 mpg highway.

I will be ordering a 2021 F150 4x2 King Ranch with 5.0L, 10 spd auto, 3.31 gears. I am anticipating excellent highway mpgs.
 

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I currently have 3.73's with the 5.0 and will go with them again on the 21 model with max tow..

21 models have larger tires too.. 3%.. But it all adds up..
 

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I currently have 3.73's with the 5.0 and will go with them again on the 21 model with max tow..

21 models have larger tires too.. 3%.. But it all adds up..
What year and mpg do you get on current truck?
 

SJLCJL

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What year and mpg do you get on current truck?
Oh yeah, sorry.. Currently have a '13 with the 6 speed of course..
I have a lifetime MPG of 16.7.. Probably a 50/50 split of city.hwy miles.. Do some towing from time to time as well.. Now on trips where it's mainly just hwy driving I get in the low 20's or so..

Based on numbers with the 10 speed and tire size and everything, I'd expect another 10% better fuel econ over what I currently have just because of final drive ratio..

If people are really concerned about fuel mileage.. Don't use cruise control.. You can get better MPG with your foot..
 

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My new truck will be equipped with the 3:73 ratio, 2021 KR 5.0
my last one 2018 Stolen was a Lariat with a 5.0, exactly like my 2010 and 2016,
I pull a 8800 lb double axle trailer and a 5500 lb Boat when possible, I won’t buy any truck with another axle ratio, the V8 at 110kmh run at around 1800 and got very good mileage on the Highway at 110Kmph average of 10 liter (4.5 liter per imp gal) per hundred kilometre. That’s around 30mpg, note imperial gallon is slightly bigger. All my truck are always cruise control driven when possible. the air/fuel ratio injection is at is best on the cruise control ECM take care of the mix better. And the engine is running at is best, for the V6 I don’t know as I won’t drive one for sure.
best regards
 
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Knickell

Knickell

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Thank each of you for the input! I’ve searched several other sites too, and you all have put forward the most succinct information which is appreciated.

Is anyone out there running the 3.31s on earlier F-150s? If so, how’s your fuel economy and performance overall driving around with no tow?
 

UNIKRN150

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I wen
Thank each of you for the input! I’ve searched several other sites too, and you all have put forward the most succinct information which is appreciated.

Is anyone out there running the 3.31s on earlier F-150s? If so, how’s your fuel economy and performance overall driving around with no tow?
I went with the 3:31 e-lock on my Reg Cab, Short Bed XLT coyote. I have an hour and a half freeway commute (not that I plan to use it for commuting much) and most of my towing will be at low speeds on dirt roads in 4x4 so I don't think torque is going to be a towing issue for me. With the 122 wheel base I'm already 1000lbs ahead of the game on asphalt city driving.
I expect to get delivery of my truck sometime in the 21st century so I'll post how it worked out once I can.
...if we're still using the internet by then!
 

Bryan Simon

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I also have the 3.31 gearing in the new truck. (5.0)
with the low gearing of the trans, I am pretty confident this truck will drag most anything I will ever drag with it up to 10-11,000.
Unladen it is plenty responsive and has no trouble moving out.
since most all of my usage is rural/empty, I really don’t have a regular need for shorter rear gears.
It might struggle a bit at Cruise hauling a heavy load, but I am not adverse to winding it up a bit to keep on going.
My old 79 Chev has a 454/4spd and .3.08 rear.
never had a real issue with that thing even pulling grades, I would wind it up tho and watch the tach and fuel gauge try to meet in the middle.
If I have to stay out of the overdrives or even 7 or 6 to get the job done, so be it. For as little time that mine will be dragging stuff, not worth it in the long run for the fuel mileage.
if it goes below 10mpg while actually workin, I’m certainly not gonna get uptight about it.
 

Agashi25

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3.73 on my 5.0 and I love that pull!! I wouldn’t change them.
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