GMC 2012 Sierra Denali Owner's Manual page 262

By positioning four 5 cm (2 in) by
15 cm (6 in) wooden planks
across the width of the pickup
box, you can create an upper
load platform. The planks must
be inserted in the pickup box
depressions. The length of the
planks must allow for at least a
2 cm (0.75 in) bearing surface on
each end of the plank.
When using this upper load
platform, be sure the load is
securely tied down to prevent it
from shifting. The load's center
of gravity should be positioned
in a zone over the rear axle.
The zone is located in the area
between the front of each wheel
well and the rear of each wheel
well. The center of gravity height
must not extend above the top
of the pickup box flareboard.
Any load that extends beyond
the vehicle's taillamp area must
be properly marked according to
local laws and regulations.
Remember not to exceed the
Gross Axle Weight Rating
(GAWR) of the front or rear axle.
When you carry removable items,
you may need to put a limit on how
many people you carry inside your
vehicle. Be sure to weigh your
vehicle before you buy and install
the new equipment.
Remember not to exceed the
Gross Axle Weight Rating
(GAWR) of the front or rear axle.
Ladder Rack 340 kg
and Cargo (750 lbs)
Cross Toolbox 181 kg
and Cargo (400 lbs)
Side Boxes 113 kg per
and Cargo side (250 lbs
per side)
*The combined weight for all
rail-mounted equipment should
not exceed 454 kg (1,000 lbs).
A reinforcement kit for
rail mounted add on
equipment is recommended.
See your GM dealer.