Buick 2006 Rainier Maintenance Manual page 307

The trailer tongue weight (A) should be 10 percent to
15 percent of the total loaded trailer weight, up to a
maximum or 400 lbs (181 kg) with a weight carrying hitch.
The trailer tongue weight (A) should be 10 to 15 percent
of the total loaded trailer weight, up to a maximum of
750 lbs (340 kg) with a weight distributing hitch.
Do not exceed the maximum allowable tongue weight
for your vehicle. Choose the shortest hitch extension
that will position the hitch ball closest to the vehicle.
This will help reduce the effect of trailer tongue weight
on the rear axle.
After you've loaded your trailer, weigh the trailer and
then the tongue, separately, to see if the weights
are proper. If they aren't, you may be able to get them
right simply by moving some items around in the
trailer.
Trailering may 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.
4-55