GMC 2009 Sierra - Manual (Page 305)

The weight at the rear axle could be 850 lbs (386 kg) X
1.5 = 1,275 lbs (578 kg). Since the rear axle already
weighs 2,700 lbs (1 225 kg), adding 1,275 lbs (578 kg)
brings the total to 3,975 lbs (1 803 kg). This is very
close to, but within the limit for RGAWR as well. The
vehicle is set to trailer up to 8,500 lbs (3 856 kg).
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.
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