2007 Jeep Grand Cherokee Owner's Manual - Page 291
2007 Jeep Grand Cherokee Manual
Page 291 highlights
STARTING AND OPERATING 291 WARNING! Fast spinning tires can be dangerous. Forces generated by excessive wheel speeds may cause tire damage or failure. A tire could explode and injure someone. Do not spin your vehicle's wheels faster than 35 mph (55 km/h) when you are stuck, and do not let anyone near a spinning wheel no matter what the speed. Tread Wear Indicators Tread wear indicators are in the original equipment tires to help you in determining when your tires should be replaced. 5 These indicators are molded into the bottom of the tread grooves and will appear as bands when the tread depth becomes 1/16 inch (2 mm). When the indicators appear in 2 or more adjacent grooves, the tire should be replaced. Many states have laws requiring tire replacement at this point.