Jeep 2005 Grand Cherokee - Manual (Page 267)

Tread Wear Indicators
These indicators are narrow strips 1/16 inch (1.6 mm)
thick and are found in the tread pattern grooves.
When the tread pattern is worn down to these treadwear
indicators, the tires should be replaced.
Overloading your vehicle, long trips in very hot weather,
and driving on bad roads may result in greater wear.
Replacement Tires
The tires on your new vehicle provide a balance of many
characteristics. They should be inspected regularly for
wear and correct inflation pressure. The manufacturer
strongly recommends that you use tires equivalent to the
originals in quality and performance when replacement
is needed (see section on tread wear indicators). Failure
to use equivalent replacement tires may adversely affect
the safety, handling, ride and fuel economy of your
vehicle. We recommend that you contact your original
equipment tire dealer on any questions you may have on
tire specifications or capability.
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