Pontiac Vibe 2003 Owner's Manual page 117

To adjust the position of the crossrails, do the following:
1. Turn the eight knobs counterclockwise to loosen the
crossrails.
2. Slide the crossrails to the desired position for loading
the luggage.
3. After adjusting the crossrails, be sure to tighten all
the knobs by turning the knobs clockwise.
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NOTICE:
Loading cargo that weighs more than 75 lbs.
(34 kg) on the luggage carrier may damage your
vehicle. When you carry large things, never let
them hang over the rear or the sides of your
vehicle. When loading cargo, be sure it rests on
the crossrails and does not scratch or damage
the vehicle.
Put the cargo against the side rails and fasten it
securely to the luggage carrier. Put the main
weight as far forward as you can and move the
rear crossrail forward as far as possible to keep
the load from shifting.
Don't exceed the maximum vehicle capacity when
loading your vehicle. For more information on vehicle
capacity and loading, see "Loading Your Vehicle" in
the Index.
To prevent damage or loss of cargo as you're driving,
check now and then to make sure the luggage carrier and
cargo are still securely fastened.