Buick 2006 Rendezvous Owner's Manual page 320

Trailering may also be limited by the vehicle's ability to
carry tongue weight. Tongue weight cannot cause the
vehicle to exceed the GVWR (Gross Vehicle Weight
Rating) or the RGAWR (Rear Gross Axle Weight Rating).
The effect of additional weight may reduce your trailering
capacity more than the total of the additional weight.
Consider the following example:
A vehicle model base weight is 5,500 lbs (2 495 kg);
2,800 lbs (1 270 kg) at the front axle and 2,700 lbs
(1 225 kg) at the rear axle. It has a GVWR of 7,200 lbs
(3 266 kg), a RGAWR of 4,000 lbs (1 814 kg) and a
GCWR (Gross Combination Weight Rating) of
14,000 lbs (6 350 kg). The trailer rating should be:
You can expect tongue weight to be at least
10 percent of trailer weight (850 lbs (386 kg)) and
because the weight is applied well behind the rear axle,
the effect on the rear axle will be greater than just
the weight itself, as much as 1.5 times as much.
4-42
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.