F150 3.31 gears vs 3.55 gears

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.

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.

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.

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

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.

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.