GMC 2009 Savana Van Owner's Manual page 316

GM recommends replacing tires in sets of four (or six
if your vehicle has dual rear wheels). This is because
uniform tread depth on all tires will help keep your vehicle
performing most like it did when the tires were new.
Replacing less than a full set of tires can affect the
braking and handling performance of your vehicle.
See Tire Inspection and Rotation on page 5-70 for
information on proper tire rotation.
CAUTION:
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Mixing tires could cause you to lose control
while driving. If you mix tires of different
sizes, brands, or types (radial and bias-belted
tires) the vehicle may not handle properly,
and you could have a crash. Using tires of
different sizes, brands, or types may also
cause damage to your vehicle. Be sure to
use the correct size, brand, and type of tires
on your vehicle's wheels.
5-74
CAUTION:
{
If you use bias-ply tires on the vehicle,
the wheel rim flanges could develop cracks
after many miles of driving. A tire and/or
wheel could fail suddenly, causing a crash.
Use only radial-ply tires with the wheels on
the vehicle.
If you must replace your vehicle's tires with those that
do not have a TPC Spec number, make sure they are the
same size, load range, speed rating, and construction
type (radial and bias-belted tires) as your vehicle's
original tires.
Vehicles that have a tire pressure monitoring system
could give an inaccurate low-pressure warning if
non-TPC Spec rated tires are installed on your vehicle.
Non-TPC Spec rated tires may give a low-pressure
warning that is higher or lower than the proper warning
level you would get with TPC Spec rated tires. See Tire
Pressure Monitor System on page 5-65.
Your vehicle's original equipment tires are listed on
the Tire and Loading Information label. See Loading the
Vehicle on page 4-18, for more information about the Tire
and Loading Information label and its location on your
vehicle.