Ford 1996 Crown Victoria Manual page 278

Replacing the Tires
Replace any tires that show wear bands. When
your tire shows a wear band, it has only
1/16 inch (2 mm) of tread left.
A worn-out tire
Because your vehicle's tires may wear unevenly,
you may need to replace them before a wear
band appears across the entire tread. Some spots
wear more heavily than others.
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.
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