GMC Sierra 2008 Owner's Manual page 375

But let's say your specific vehicle is equipped with some
of the latest options and you have a front seat passenger
and two rear seat passengers with some luggage and
gear in the vehicle as well. You may add 300 lbs (136 kg)
to the front axle weight and 400 lbs (181 kg) to the rear
axle weight. Your vehicle now weighs:
Weight is still below 7,200 lbs (3 266 kg) and you may
think that you should subtract 700 additional pounds
(318 kg) from your trailering capacity to stay within
GCWR limits. Your maximum trailer would only
be 7,800 lbs (3 538 kg). You may go further and think
you must limit tongue weight to less than 1,000 lbs
(454 kg) to avoid exceeding GVWR. But, you must
still consider the effect on the rear axle. Because your
rear axle now weighs 3,100 lbs (1 406 kg), you can
only put 900 lbs (408 kg) on the rear axle without
exceeding RGAWR. The effect of tongue weight is
about 1.5 times the actual weight. Dividing the
900 lbs (408 kg) by 1.5 leaves you with being able
to handle only 600 lbs (272 kg) of tongue weight.
Since tongue weight is usually at least 10 percent of
total loaded trailer weight, you can expect that the
largest trailer your vehicle can properly handle is
6,000 lbs (2 721 kg).
It is important that you make sure your vehicle does
not exceed any of its ratings — GCWR, GVWR,
RGAWR, Maximum Trailer Rating or Tongue Weight.
The only way to be sure you are not exceeding any
of these ratings is to weigh your vehicle and trailer.
Total Weight on Your Vehicle's Tires
Be sure your vehicle's tires are inflated to the upper
limit for cold tires. You'll find these numbers on
the Certification label at the rear edge of the driver's
door or see Loading Your Vehicle for more information.
Then be sure you don't go over the GVW limit for
your vehicle, or the GAWR, including the weight of the
trailer tongue. If you use a weight distributing hitch,
make sure you don't go over the rear axle limit before
you apply the weight distribution spring bars.
Hitches
It's important to have the correct hitch equipment.
Crosswinds, large trucks going by and rough roads
are a few reasons why you'll need the right hitch.
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