I am trading my big Ford F250 off and probably going with a 2011 Ecoboost.

I pull a livestock alluminum trailer about 20 days of the year, and the trailer loaded usually weighs between 5,000 and 9,000. Most of the time being closer to 5,000.
The top end suggested towing for 3.55 is 9,600 vs 11,200 for the 3.73.

I know I will lose alot of gas mileage with the 3.73. So my question is, will I hurt the truck if I occasionally want to pull 9,500 lbs.
Will I notice a big difference in pulling with a 3.73 vs a 3.55.

Most of the time its just the truck and I am not pulling and that is what has me leaning towards a 3.55 but I dont want to be in trouble if I do pull the trailer loaded at 9,500 lbs.

Thanks for any tips.

 

If I were in your shoes, I would go for the 3.73's. Yes, you will lose a little fuel mileage, but it won't be that bad if you drive conservatively.

And if you live where there are hills, you will be much happier with the lower gears.

 

in 4th gear that would relate to about 250-300 rpm difference for each .25 gear ratio change...just to give you an idea

 

20 days per year. Go with 3:55 and let the transmission worry about it. CB

 

Another thing to consider is that when you're towing, you will probably want LT tires instead of the P-Series that would usually be on a F-150. In many cases an LT tire would be a shade taller than the closest P-Series tire. In that case, going with 3.73 gears would probably be a wash.

 

Since you don't tow that often, go for the 3.55s for MPG. If you need more power while towing every now and then maybe just lock it out of overdrive.

 

Im all about the peace of mind, the pennys saved on the MPG is more in your foot than anything else, I vote 3.73's all the way, help your truck help itself......Your not going to have the heavy chassis of the super duty

 

The Ecoboost will pull with 3.55's, there is a lot of torque in that motor. As for towing mileage, my old 5.4 got about 8 mpg pulling my camper, and my Ecoboost with the same camper gets between 8.5 and 9.5. You wont get diesel fuel economy, but it's no worse than a big V8.

 

WOW! That's a big dip in fuel economy... My 460 (7.5l), C6 (no OD gear), 4.56 gears, 33" tires, gets 9 mpg pulling 8k. Guess that just shows how much more a smaller engine has to work. Of course, my 460 also gets 10-11 mpg without a load...

 

Don't get too excited. He's probably moving 20 mph faster than you.

 

Except for the largest hills the 3.55's won't even know that trailer is back there and it will be easier on fuel.

 

I usually don't jump into these types of "which gears to get" threads, but hopefully this will help out the OP.

I keep seeing posts saying that 3.73's will hurt economy over 3.55's and I hope I don't make a bunch of enemies But if you keep the speed down you'll actually pull better mpg's with the more aggressive gears. With more aggressive gearing it's as if your truck is driving downhill all the time. There is less leverage against your motor. And with the slightly higher rpm's you're closer to peak volumetric efficiency. As long as you stay below your peak torque rpm, you'll actually get better mpg with the more aggressive gearing no matter what.

I run a truck with 4.88's in the rear end and 31" tires. At 80 it's spinning 3000 rpm.Obviously if I drive around everywhere doing 80 I'll get horrible mileage, but short bursts are fine. Our last road trip to Northern California averaging 73mph it got 16mpg average. At that speed you barely crack open the throttle and use less fuel.

Back in the 60's and 70's all the drag racers were putting 4.11's in their cars with 3 speed transmissions and no overdrive. You couldn't go past 55. At that speed you were pulling 4000 rpm and the carburetor sucked down the gas LOL. so rear gearing got a bad name and it's carried well into the 21st century. Just calculate what your rpm will be at the cruise speed you want to hold and gear it to that. Choose an rpm that is about 400 rpm below peak torque.

 

That's not true with highway driving. MPG is "miles / gallons". If I can increase miles 10% by using 5% more fuel, then it's a win. If you plot MPG vs. speed then you'll find the shape of the curve is a hump. Go too slow and you're below the peak. Go too fast and you're below the peak. The answer is to go the right speed, not just slower speed. www.fueleconomy.gov has an example of what the shape of the curve looks like, if you're interested.

Also, there's less need for aggressive gearing in the rear axle these days because the 1st gear ratio in the modern 6 speed is nearly twice that of the old 3 speeds. The final gear ratio is just as aggressive, yet has deep overdrive to improve MPG at higher speed.

Example:
Final gear ratio of TH400 in 1st gear with 4.88 rear gear --> 12.1
Final gear ratio of new F150 in 1st gear with 3.55 rear gear --> 14.8 (Giddyup, baby!)

 

You are sooo right...that's why I posted the est rpm change...its so minimal in reality and if its borderline, yeah go for it, if you really need it based on the power band, then it gives you a gut instinct of about what gears you really need!!!!

 

If it's of any help, my 4X4 Screw with Ecoboost and 3.73 is turning 2000 RPMs at 70 MPH.