Buick 2002 Rendezvous Owner's Manual page 158

Roof Rack System (Option)
CAUTION:
If you try to carry something on top of your
vehicle that is longer or wider than the luggage
--
carrier like paneling, plywood, a mattress, and
--
so forth the wind can catch it as you drive
along. This can cause you to lose control. What
you are carrying could be violently torn off, and
this could cause you or other drivers to have a
collision, and of course damage your vehicle. You
may be able to carry something like this inside.
But, never carry something longer or wider than
the luggage carrier on top of your vehicle.
2-66
If you have the luggage carrier, you can load things on
top of your vehicle. If you do load things on the top
of your vehicle, you must load them on the luggage
carrier crossrails.
NOTICE:
Damage may be caused to the roof of your vehicle
if anything is placed directly on the roof.