GMC 2004 Savana - Manual (Page 307)

Tire Size
The following examples show the different parts of a
tire size.
(A) Passenger (P-Metric) Tire: The United States
version of a metric tire sizing system. The letter “P” as
the first character in the tire size means a passenger
vehicle tire engineered to standards set by the U.S. Tire
and Rim Association.
(B) Tire Width: The three-digit number indicates the
tire section width in millimeters from sidewall to sidewall.
(C) Aspect Ratio: A two-digit number that indicates
the tire height-to-width measurements. For example, if
the tire size aspect ratio is “75,” as shown in item “C” of
the illustration, it would mean that the tire’s sidewall is
75% as high as it is wide.
(D) Construction Code: A letter code is used to
indicate the type of ply construction in the tire. The letter
“R” means radial ply construction; the letter “D” means
diagonal or bias ply construction; and the letter “B”
means belted-bias ply construction.
(E) Rim Diameter: Diameter of the wheel in inches.
(F) Service Description: The service description
indicates the load range and speed rating of a tire. The
load index can range from 1 to 279. Speed ratings
range from “A” to “Z”. Passenger (P-Metric) Tire
5-61