F150 3.31 gears vs 3.55 gears
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...
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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.
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.
