Mercury 2002 Cougar Owner's Manual page 197

Four tire rotation
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.
Maintenance and Specifications
197