F150 3.31 gears vs 3.55 gears

[plasticmaster]

I accidentally posted this in the wrong section earlier, but please indulge me in 1 more question. I sort of asked this in another thread, but wanted to devote a thread to this particular question. My current truck is a 2014 Silverado 5.3L with payload capacity of 1638# and 9700# tow capacity as I have the 3.42 gear ratio. I tow a TT that's close to 9500# loaded and it tows it very comfortably. I'm looking at getting a 2015 to 2020 Ford F150. The payload capacity of the F150 will be greater than my Silverado, so I'm good there, but the tow capacity will either be 9100 or 10100 depending on whether I get the 3.31 gears or the 3.55 gears. Do I really need to be that worried about which gear ratio? Would it really make that much of a difference towing my camper? Please refrain from telling me I need a 3/4 ton or 1 ton truck as I'm looking for the answer about the gear ratio. Thanks.

[Golden_HVAC]

I would rather have the 3.31:1 rear axle ratio, than the 3.55:1 ratio. I don't think it would manner if you are towing 10,000 pounds, the truck will not magically blow up because you are towing 300 or 500 more pounds than the recommended amount of weight.

Of course buying used truck, it is nearly impossible to pick a rear axle ratio, as you are relying on the dealership back in 2015 deciding to order a bunch of F-150's with either the 3.31 or 3.54 rear axle. And the new buyer picking the truck that you want, and now wanting to sell it today.

Not actually good odds, and I would not hold my breath until the right rear axle ratio shows up. Just buy the pickup and enjoy it. Know that the 3.31 ratio will typically get slightly higher MPG. But who really cars? If you drive the truck only about 5,000 miles a year, then you will perhaps spend as much on insurance as gas.

[time2roll]

Get a good deal on a good truck. If the ratio makes it a dog... a quick $1200 or so will get you into 3.55 3.73 4.10 as you see fit. x2 if 4WD.

[C_Schomer]

Get 3.55… especially after driving a friends with 3.31 and he was even sorry he got 3.31. We both agreed the 3.31s killed too much performance. Craig

[Turtle_n_Peeps]

valhalla360 wrote:
Unless you have some special reason to consider it...just plain silly to get a truck rated for 9100lb when you know the trailer scaled at 9500lb. Also, take a look at the CGVWR in case you have a lot of stuff in the truck.

Transmission makes a huge difference. If both trucks have a tow rating in excess of 9500lb, all else being equal, I would take the 3.31 with the 10 speed transmission. With the 6 speed, I'm more ambivalent. (older trucks with 4/5 speed transmissions the rear end can make a big difference)

Why?

Under normal non-towing, you will likely get better MPG with the 3.31.
There is an ideal RPM range to get good power and efficiency under a given load.
- In the old days, if you had to drop down a gear, your RPM made a big jump and there was a good chance, you jumped over that sweet spot, so the engine does it but at excessive non-efficient RPM. By using the deeper rear end, you could hold top gear with the engine RPM in the sweet spot (under most conditions).
- With the 10 speed, dropping down a gear is a much smaller jump in RPM, so even with the 3.31, you likely can get the motor in the sweet spot when the transmission picks a gear.

The motor only cares about the overall gear ratio...same ratio in 9th with the 3.55 vs 8th with the 3.31, the motor doesn't care.

The only place this doesn't apply is if you push the upper limits of the tow rating. If the tow rating is only 9100lb, you are more likely to reach the point where there are no more gears to drop down in mountains or you could potentially be over stressing the gears in the rear end leading to shorter lifespan/failures.

Great post as always Mike.

[valhalla360]

Unless you have some special reason to consider it...just plain silly to get a truck rated for 9100lb when you know the trailer scaled at 9500lb. Also, take a look at the CGVWR in case you have a lot of stuff in the truck.

Transmission makes a huge difference. If both trucks have a tow rating in excess of 9500lb, all else being equal, I would take the 3.31 with the 10 speed transmission. With the 6 speed, I'm more ambivalent. (older trucks with 4/5 speed transmissions the rear end can make a big difference)

Why?

Under normal non-towing, you will likely get better MPG with the 3.31.
There is an ideal RPM range to get good power and efficiency under a given load.
- In the old days, if you had to drop down a gear, your RPM made a big jump and there was a good chance, you jumped over that sweet spot, so the engine does it but at excessive non-efficient RPM. By using the deeper rear end, you could hold top gear with the engine RPM in the sweet spot (under most conditions).
- With the 10 speed, dropping down a gear is a much smaller jump in RPM, so even with the 3.31, you likely can get the motor in the sweet spot when the transmission picks a gear.

The motor only cares about the overall gear ratio...same ratio in 9th with the 3.55 vs 8th with the 3.31, the motor doesn't care.

The only place this doesn't apply is if you push the upper limits of the tow rating. If the tow rating is only 9100lb, you are more likely to reach the point where there are no more gears to drop down in mountains or you could potentially be over stressing the gears in the rear end leading to shorter lifespan/failures.

[Grit_dog]

lane hog wrote:
Here's another vote for the 3.55... My 3.5 Eco+MaxTow with the 3.55 pulls 9,000 lbs of trailer fairly well. We've got 11% grades on gravel roads at my brother-in-law's property in TN, and the Ford handled that with no hesitation or slippage.

Which is about 99.9% NOT any indicator of "towing capacity".
I could tow 9klbs up an 11% gravel road in 4LO in my 50 year old 100hp CJ5. Or in 2HI if I could start out on the flats and get it rolling in 1st gear before hitting the grade.

Not doubting that your rig also tows quite well.

[dodge_guy]

Since you have a choice. Always go with the lower (numerically higher gear when towing heavy. Even with the transmissions with 8 and 10 speeds.

[lane_hog]

Here's another vote for the 3.55... My 3.5 Eco+MaxTow with the 3.55 pulls 9,000 lbs of trailer fairly well. We've got 11% grades on gravel roads at my brother-in-law's property in TN, and the Ford handled that with no hesitation or slippage.

[theoldwizard1]

MitchF150 wrote:

Anyway, the OP wants a 5.O V8, so a different beast than my Ecoboost, but I would not want that 5.0 towing my little #7000 TT.. 🙂

Properly equipped, a F150 with a 2.7L EcoBoost and 3.73 rear axle, has a max tow rating of 10,000 lbs ! The 2.7L max only 10 less lb-ft of torque (400 vs 410) as the 5.0L and at a lower RPM (3000 vs 4250).

[theoldwizard1]

MitchF150 wrote:

I have 3.73's with a 13 F150, but that's a different apple compared to the 15 and up F150's, so can't really compare, other than the Ecoboost and the 6 speed trans for the most part.

Depending on the engine and payload package some F150s still come with 3.73.

[theoldwizard1]

I can not say for all model years in question, but Ford Trailer Tow Packages usually come with an upgraded radiator and transmission cooler. IMHO, those a key to engine and transmission longevity.

You would definitely be better off with the 10 speed transmission.

[Grit_dog]

Now, you're looking for as old as 2015 models? 6 speed will not cover up the higher gearing as well as the newer 10 speeds.
And the older model will have a few less ponies.

[MitchF150]

Yep... Even with my 3.73's I always lock out 6th gear.. and that's just cruising on the flats..

Up the grades, it likes 4th. Even just some of those gradual inclines, I'll manually shift to 4th.

Since I have the Ecoboost, if you give the engine some beans, the boost goes WAY UP. If you are only chugging along at <2000 rpms, you can be pushing some 10+ psi of boost and not even see any speed increase! Plus, the temps start to rise pretty fast..

Bump it into 4th, and the boost goes down to arouund 5 psi and you actually pick up speed and keep temps in check and actually get better mpg's..

That's why running in 5th is better than 6th when towing. Going the same speed, there is at least a +- 4 psi boost difference running in 6th compared to 5th and temps increase and mpg's drop running in 6th. (while towing... )

I didn't find any of this out until I got an ODB2 plug in and phone app to monitor a ton of sensors that the dash does not even come close to showing you...

Anyway, the OP wants a 5.O V8, so a different beast than my Ecoboost, but I would not want that 5.0 towing my little #7000 TT.. 🙂

Mitch

[Lwiddis]

I agree with Mitch…3.55 if the F150 has a six speed transmission.