Originally Posted by bpiazza
We are driving a 2009 Ford 1-150 Lariat that was upgraded with a tow package, brake controller, etc.
According to the 2009 Ford RV and trailer towing guide, your truck has a "tow rating" of between 5,700 and 11,100 pounds gross trailer weight. If you want a better estimate than that, then we need more info about your truck:
Cab (regular, SuperCab or Super Crew)
Wheelbase = 126, 132.5, 145, 157, or 163
drivetrain = 4x2 or 4x4
axle ratio = 3.31, 3.55, 3.73, regular or e-locker
engine = 4.6L 2V, 4.6L 3V, or 5.4L
GVWR = per the doorsticker that also tells you the VIN, month/year of assembly, tire size and PSI, front and rear GAWR, and several codes such as for paint and axle.
So just guessing at which F-150 you might have, a common rig used for towing 26-29 ft TTs would be a
145" wheelbase (5.5' bed)
3.55 e-locker axle
That truck has a GCWR of 15,500 and a tow rating of 9,700 pounds. That means it could PULL
a trailer that weighs up to 9,700 pounds. But if there's anything in the F-150 except a skinny driver, it cannot HAUL
the hitch weight of anywhere near that much trailer.
That truck when wet and loaded ready for towing, with passengers and normal tools and cargo, will weigh about 6,600 pounds. That leaves only 600 pounds for hitch weight, or if 12.5% is a good estimate of wet and loaded hitch weight, then a max trailer weight of 4,800 pounds.
We are looking at 26-29 ft trailers with a dry weight of 4-6000 lbs and I am trying to figure out how that will pull.
Dry weight is a useless number. What is the GVWR of the trailer you want? Almost everyone will have their TT loaded to the GVWR by the middle of their third RV trip, so use the GVWR of the trailer as the wet and loaded weight of the trailer when matching trailer to tow vehicle.
But if you have the exact truck described above, then any wet and loaded trailer weight more than about 4,800 pounds will cause you to be overloaded.
I am hoping the people who respond have real-life experience - I have had way too many people give me hypothetical measurements and "if your tow capacity is ____ then you should be fine with ____"
It will be a rare bird that has towed a TT with your truck. I've towed all sorts of trailers with all sorts of tow vehicles for over 50 years, but never with a truck exactly like yours.
Here's my Current setup:
2012 F-150 Lariat SuperCrew 6.5' bed EcoBoost with 3.15 axle ratio and e-locker differential, GVWR 7,100 pounds, GCWR 14,000 pounds, tow rating 8,400 pounds. TT is 2012 Skyline Nomad 196S with GVWR of 5,600 pounds, wet and loaded weight of 4,870 pounds on a recent long trip. (4220 trailer axle weight plus 650 pounds tongue weight).
The CAT scale said the front truck axle weighed 3360 and the rear truck axle weighed 3,840 for a GVW of 7,200 pounds on the 4 truck tires. Gross combined weight (GCW) was 11,420
Overloaded by 100 pounds. And my trailer weighed only 4,870 pounds, nowhere near the 8,400 tow rating. And my GCW was nowhere near the GCWR of the F-150. What happened?
GVWR of the tow vehicle bit me in the butt. I was nowhere near the 14,000 GCWR, but over the GVW of the F-150. Common for F-150s that do not have the Heavy Duty Payload Package.
since we are buying new and that is a big chunk of change, I would like more assurance than that....
I can tell you how how to properly size your trailer weight to match the capabilities of the truck. You need only two bits of info,  the GVWR of your truck and  the weight of your wet and loaded truck.
You need to know the actual weight of your wet and loaded truck without the trailer. So load the truck with driver, passengers, pet(s), tools, jacks, options such as toolbox and bedliner or bedrug (mine has both), the shank and ball mount of your weight-distributing hitch, and anything else that might be in the truck when towing. Drive to a truckstop that has a truck scale and fill up with gas. Then weigh the wet and loaded truck. (If you don't already have the WD hitch, then estimate 50# for the shank and ball mount and add that to your scale weight.)
Subtract the weight of the wet and loaded truck from the GVWR and that will be the max hitch weight you can have without being overloaded.
TT hitch weight varies from about 12% to 15% or a bit more (mine is almost 16%). Some say as low as 10 percent, but I've yet to meet one of those rascals. So I use 15% when trying to match trailer to tow vehicle.
So divide your max hitch weight by 15% (0.15) and the answer will be the max GVWR of any tandem-axle TT you should consider. If your truck has a GVWR of 7200 pounds, you'll probably be disappointed at how light a TT you'll have to find.
If your truck has GVWR of 8,400 pounds, then the weight of the TT you can consider goes way up. You won't be overloaded like I am with a TT that weighs only 4,870 when wet and loaded for the road.