Ford 1998 Windstar Owner's Manual page 295

Replacing the Tires
Replace tires that show wear bands. When your tire shows a
wear band, it has only 1/16 of an inch (1.59 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.
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.
Make sure that all replacement tires are of the same size,
type, load-carrying capacity, and tread design (e.g. "All
Terrain", etc.), as originally offered by Ford.
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