Ford 2004 F150 Owner's Manual page 176

Driving
GCW (Gross Combined Weight) – is the weight of the loaded vehicle
(GVW) plus the weight of the fully loaded trailer.
GCWR (Gross Combined Weight Rating) – is the maximum allowable
weight of the vehicle and the loaded trailer – including all cargo and
passengers – that the vehicle can handle without risking damage.
(Important: The towing vehicle's braking system is rated for operation at
GVWR, not at GCWR. Separate functional brakes should be used for safe
control of towed vehicles and for trailers where the GCW of the towing
vehicle plus the trailer exceed the GVWR of the towing vehicle. The
GCW must never exceed the GCWR.
Maximum Loaded Trailer Weight – is the highest possible weight of a
fully loaded trailer the vehicle can tow. It assumes a vehicle with only
mandatory options, no cargo (internal or external), a tongue load of
10–15% (conventional trailer) or king pin weight of 15–25% (fifth wheel
trailer), and driver only (150 lbs [68 kg]). Consult your dealership (or
the RV and Trailer Towing Guide provided by your dealership) for
more detailed information.
Tongue Load or Fifth Wheel King Pin Weight – refers to the amount
of the weight that a trailer pushes down on a trailer hitch.
Examples: For a 5,000 lbs. (2,268 kg) conventional trailer, multiply
5,000 by 0.10 and 0.15 to obtain a proper tongue load range of 500 to
750 lbs. (227 to 340 kg). For an 11,500 lbs. (5,216 kg) fifth wheel trailer,
multiply by 0.15 and 0.25 to obtain a proper king pin load range of 1,725
to 2,875 lbs. (782 to 1,304 kg)
Do not exceed the GVWR or the GAWR specified on the
certification label.
Do not use replacement tires with lower load carrying capacities
than the originals because they may lower the vehicle's GVWR
and GAWR limitations. Replacement tires with a higher limit than the
originals do not increase the GVWR and GAWR limitations.
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