Buick 2005 Rainier Owner's Manual page 297

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
900 lbs (408 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.
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 on page 4-43 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.
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