Lincoln 1997 Town Car Owner's Manual page 238

Because your vehicle's tires may wear unevenly,
you may need to replace them before a wear band
appears across the entire tread.
WARNING
When replacing full size tires, never
mix radial, bias-belted, or bias-type
tires. Use only the tire sizes that are
listed on the tire pressure decal. Make
sure that all tires are the same size,
speed rating, and load-carrying capacity.
Use only the tire combinations
recommended on the decal. If you do
not follow these precautions, your
vehicle may not drive properly and
safely.
Tires that are larger or smaller than your vehicle's
original tires may also affect the accuracy of your
speedometer.
236
Information About Tire Quality Grades
New vehicles are fitted with tires that have their
Tire Quality Grade (described below) molded into
the tire's sidewall. These Tire Quality Grades are
determined by standards that the United States
Department of Transportation has set.
Tire Quality Grades apply to new pneumatic tires
for use on passenger cars. They do not apply to
deep tread, winter-type snow tires, space-saver or
temporary use spare tires, tires with nominal rim
diameters of 10 to 12 inches or limited production
tires as defined in Title 49 Code of Federal
Regulations Part 575.104(c)(2).
U.S. Department of Transportation — Tire
quality grades: The U.S. Department of
Transportation requires Ford to give you the
following information about tire grades exactly as
the government has written it.