Pontiac Montana SV6 2007 Owner's Manual page 400

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. The weight at the rear axle could be
850 lbs (386 kg) X 1.5 = 1,275 lbs (578 kg).
400
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).