Ford 2002 Crown Victoria Manual page 223

Replacing the tires
Replace the tires when the wear
band is visible through the tire
treads.
When replacing full size tires, never mix radial bias-belted, or
bias-type tires. Use only the tire sizes that are listed on the
Certification or Tire Label. Make sure that all tires are the same size,
speed rating, and load-carrying capacity. Use only the tire combinations
recommended on the label. If you do not follow these precautions,
your vehicle may not drive properly and safely.
Make sure that all replacement tires are of the same size, type,
load-carrying capacity and tread design (e.g., "All Terrain",
"Touring", etc.), as originally offered by Ford.
Failure to follow these precautions may adversely affect the
handling of the vehicle and make it easier for the driver to lose
control and roll over.
Tires that are larger or smaller than your vehicle's original tires may also
affect the accuracy of your speedometer.
Maintenance and Specifications
223