smokeywren

Best for what? As XtraLargeTall mentioned, your 3.73 is best for heavier trailer towing, and the taller ratios are best for better for unloaded MPG.

With your 5.0L engine and 18" tires, Ford says your 3.73 gears are good for a trailer that weighs up to about 9,000 pounds. With 3.55 gears Ford says the max trailer weight would be about 7,500. 3.31 gears were not offered in 4x4s with the 5.0L engine, probably because the low performance would have been unaceptable to most F-150 4x4 buyers. And the 3.15 ratio I have is available only in 4x2s with the EcoBoost engine. Your truck would be a certified dog with the 3.15 ratio, but it's perfect in the lighter weight and more powerful EcoBoost 4x2 with 18" wheels if I don't plan to tow a trailer that weighs more than about 7,000 pounds.

Your 20" wheels are not in the towing guide, but with 3.73 gears they would be equivalent to about a 3.55 with 18" wheels. So your max trailer weight per Ford is probably about 7,500.

Ford's tow ratings are optimistic, assuming you have absolutely nothing in the tow vehicle except a skinny dirver. So subtract about 1,000 pounds from those numbers to get a realistic tow rating. In other words, your truck with 20" wheels should be able to tow a trailer grossing up to about 6,500 pounds up a mountain pass in the summertime at 55 MPH without overheating anything or burning up something in the drivetrain.

EBinMT

I have an EcoScrew long bed 4x4 with 3:31. I am happy with them. I don't plan on towing much over 7K with a half ton, fuel mileage is right around 20mpg at 70. All the power I need with pretty decent fuel mileage. My mods are bed cover and heartthrob exhaust.

Kenferg1

Towed from Knoxville, Tn to Charleston, SC today. I have XLT 4X4 EB SCREW 5.5' bed pulling a TT that loaded out weighs about 6,500 lbs. It does downshift quite a bit on steep grades, but never lower than 4th gear. This set up works for me since most of my driving is without a heavy load.

If you are a casual traveler without a lot of tow miles the 3.31 should be fine. However, if you are going heavy < 7K lbs, then I would seriously consider 3.55 or 3.73 especially if you will tow in the mountains quite a bit.

Just my 2 cents.

the best engines

This trailer says 6300 lbs. on tag - With crew & a bed full of tool boxes pulled it up east coast last summer (hot temps) with this 2010 5.4 xlt with 3.31 in tow haul all the way. Was very impressed with power & stable tranny temperature - you should be fine- plus they say Eco will out pull this 8 cyl!

smokeywren

Your tow rating is 8,000 pounds, so your wet and loaded truck is designed to handle a trailer that weighs up to about 7,000 pounds.

The tow rating of the EcoBoost engine is about the same as 5.4L 3V with the same options. So a much smaller engine with a bit more power and torque, but similar towing capability.

mastiff23

thanks for the info everyone!

11screw50

I think you're confusing wheel size and tire size. 18's and 20's can have the same overall diameter tire and in that case, there would be no effect on gearing.

As for subtracting 1000lb from the rated tow number, it is not quite that simple. Yes, you need to subtract the weight of occupants and gear but you also need to look at tongue weight with occupants and gear because in a lot of cases, that will be your limiting factor.

If your truck has a payload of 1500lb and a tow rating of 9300lb, with two adults and two kids (600lb total) and 200lb of gear, you're left with 700# tongue weight...tongue weight typically being 10-15% of trailer weight means you need the trailer to be 7000lb at most but possibly less. (in fact, unless you weigh less than 100lb and have nothing in the truck, you cant even tow a 9300lb trailer that has a 15% tongue weight without going over payload).

OP: if you plan on larger tires and towing anything over 5000lb, I would probably stay away from 3.31 gears.

smokeywren

No, I was assuming Ford standard 18" wheels and tires (275/65R18) compared to Ford optional 20" tires and wheels (275/65R20). But I was wrong in the size of Ford's optional 20" tire. Ford made the 275/55R20 optional on Lariats, and it is very little difference in diameter than the stock 18" tires. So you're right. In this case the 3.73 axle ratio would be almost unaffected by replacing 275/65R18 tires with 275/55R20.

pfbz

All the available tire sized offered by Ford on the F150 are nearly identical diameters, so gearing is unaffected if you get 20" vs. 18" wheel/tires.

The 3.73's definitely feel sporty and responsive with the EcoBoost, and would be my first choice with either the 5.0 or 3.5 GTDI. 3.55 woud be the tallest ration I personally would configure a truck. Unless I lived somewhere flat, cared about MPG's more than anything else, and didn't care about acceleration. 4.11's? I have only driven them in the Raptor.