2011 Chevrolet Impala Owner's Manual - Page 304

10-48 Vehicle Care Sidewall: The portion of a tire between the tread and the bead. Speed Rating: An alphanumeric code assigned to a tire indicating the maximum speed at which a tire can operate. Traction: The friction between the tire and the road surface. The amount of grip provided. Tread: The portion of a tire that comes into contact with the road. Treadwear Indicators: Narrow bands, sometimes called wear bars, that show across the tread of a tire when only 1.6 mm (1/16 in) of tread remains. See When It Is Time for New Tires on page 10‑57. UTQGS (Uniform Tire Quality Grading Standards): A tire information system that provides consumers with ratings for a tire's traction, temperature, and treadwear. Ratings are determined by tire manufacturers using government testing procedures. The ratings are molded into the sidewall of the tire. See Uniform Tire Quality Grading on page 10‑61. Vehicle Capacity Weight: The number of designated seating positions multiplied by 68 kg (150 lbs) plus the rated cargo load. See Vehicle Load Limits on page 9‑12. Passenger (P-Metric) Tire: A tire used on passenger cars and some light duty trucks and multipurpose vehicles. Recommended Inflation Pressure: Vehicle manufacturer's recommended tire inflation pressure as shown on the tire placard. See Tire Pressure on page 10‑49 and Vehicle Load Limits on page 9‑12. Radial Ply Tire: A pneumatic tire in which the ply cords that extend to the beads are laid at 90 degrees to the centerline of the tread. Rim: A metal support for a tire and upon which the tire beads are seated.