GMC Sierra Denali 2009 Owner's Manual page 325

Weight-Distributing Hitches and Weight
Carrying Hitches
A: Body to Ground Distance
B: Front of Vehicle
When using a weight-distributing hitch, the hitch must
be adjusted so the distance (A) remains the same both
before and after coupling the trailer to the tow vehicle.
If a step-bumper hitch will be used, the bumper could be
damaged in sharp turns. Make sure there is ample
room when turning to avoid contact between the trailer
and the bumper.
If the loaded trailer being pulled will weigh more
than 5,000 lbs (2 270 kg), be sure to use a properly
mounted weight-distributing hitch and sway control of the
proper size. This equipment is very important for
proper vehicle loading and good handling when driving.
Always use a sway control if the trailer will weigh
more than these limits. Ask a hitch dealer about sway
controls.
Safety Chains
Always attach chains between the vehicle and the
trailer. Cross the safety chains under the tongue of the
trailer to help prevent the tongue from contacting
the road if it becomes separated from the hitch.
Instructions about safety chains may be provided by the
hitch manufacturer or by the trailer manufacturer. If
the trailer being towed weighs up to the vehicle's trailer
rating limit, safety chains may be attached to the
attaching point on the hitch platform. Always leave just
enough slack so the rig can turn. Never allow safety
chains to drag on the ground.
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