Pontiac 2004 Bonneville Owner's Manual page 336

(A) Tire Size: The tire size code is a combination of
letters and numbers used to define a particular
tire's width, height, aspect ratio, construction type and
service description. See the "Tire Size" illustration
later in this section for more detail.
(B) Tire Performance Criteria Specification (TPC
Spec): Original equipment tires designed to GM's
specific tire performance criteria have a TPC specification
code molded onto the sidewall. GM's TPC specifications
meet or exceed all federal safety guidelines.
(C) Department of Transportation (DOT): The
Department of Transportation (DOT) code indicates that
the tire is in compliance with the U.S. Department of
Transportation Motor Vehicle Safety Standards.
Passenger Car Tire Example
5-60