Chevrolet EXPRESS - 2011 Manual page 339

Various factors, such as
maintenance, temperatures, driving
speeds, vehicle loading, and road
conditions, influence when you
need new tires.
One way to tell when it is time for
new tires is to check the treadwear
indicators, which appear when your
tires have only 1.6 mm (1/16 in) or
less of tread remaining.
Some commercial truck tires,
including Goodyear LT225/75R16
G949 RSA and Goodyear LT225/
75R16 G933 RSD, may not have
treadwear indicators. If the tires do
not have treadwear indicators,
replace the tires when the tread
depth is down to 3.2 mm (1/8 in) for
the front tires, or 1.6 mm (1/16 in) for
the rear tires. See
and
for additional
information.
The rubber in tires ages over time.
This is also true for the spare tire,
if the vehicle has one, even if it is
not being used. Multiple conditions
affect how fast this aging takes
place, including temperatures,
loading conditions, and inflation
pressure maintenance. Tires will
typically need to be replaced due to
wear before they may need to be
replaced due to age. Consult the tire
manufacturer for more information
on when tires should be replaced.
Tires age when stored normally
mounted on a parked vehicle.
Park a vehicle that will be stored for
at least a month in a cool, dry, clean
area away from direct sunlight to
slow aging. This area should be
free of grease, gasoline or other
substances that can deteriorate
rubber.
Parking for an extended period can
cause flat spots on the tires that
may result in vibrations while
driving. When storing a vehicle for
at least a month, remove the tires or
raise the vehicle to reduce the
weight from the tires.