Saab 9-7x Owner's Manual page 332

GM recommends replacing tires in sets of four.
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 5-75
for information on proper tire rotation.
CAUTION:
{
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.
5-78
CAUTION:
{
If you use bias-ply tires on your 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 your 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 equipped with a tire pressure monitoring
system may 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 5-70.
Your vehicle's original equipment tires are listed
on the Tire and Loading Information Label.
See Loading Your Vehicle on page 4-22, for more
information about the Tire and Loading Information
Label and its location on your vehicle.