Ford F-150 2010 Owner's Manual page 230

Tires, Wheels and Loading
TIRE CARE
Inspecting your tires and wheel valve stems
Periodically inspect the tire treads for uneven or excessive wear and
remove objects such as stones, nails or glass that may be wedged in the
tread grooves. Check the tire and valve stems for holes, cracks, or cuts
that may permit air leakage and repair or replace the tire and replace
the valve stem. Inspect the tire sidewalls for cracking, cuts, bruises and
other signs of damage or excessive wear. If internal damage to the tire is
suspected, have the tire demounted and inspected in case it needs to be
repaired or replaced. For your safety, tires that are damaged or show
signs of excessive wear should not be used because they are more likely
to blow out or fail.
Improper or inadequate vehicle maintenance can cause tires to wear
abnormally. Inspect all your tires, including the spare, frequently, and
replace them if one or more of the following conditions exist:
Tire wear
When the tread is worn down to
1/16th of an inch (2 mm), tires must
be replaced to help prevent your
vehicle from skidding and
hydroplaning. Built-in treadwear
indicators, or "wear bars", which
look like narrow strips of smooth
rubber across the tread will appear
on the tire when the tread is worn
down to 1/16th of an inch (2 mm).
When the tire tread wears down to
the same height as these "wear bars", the tire is worn out and must be
replaced.
Damage
Periodically inspect the tire treads and sidewalls for damage (such as
bulges in the tread or sidewalls, cracks in the tread groove and
separation in the tread or sidewall). If damage is observed or suspected
have the tire inspected by a tire professional. Tires can be damaged
during off-road use, so inspection after off-road use is also
recommended.
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