Cadillac 2007 XLR Owner's Manual page 416

(E) Tire Ply Material: The type of cord and
number of plies in the sidewall and under the
tread.
(F) Uniform Tire Quality Grading (UTQG): Tire
manufacturers are required to grade tires
based on three performance factors: treadwear,
traction and temperature resistance. For more
information see Uniform Tire Quality Grading on
page 431.
(G) Maximum Cold Inflation Load Limit:
Maximum load that can be carried and the
maximum pressure needed to support that load.
Tire Size
The following illustration shows an example of a
typical passenger (p-metric) vehicle tire size.
416
(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
60, as shown in item C of the illustration, it would
mean that the tire's sidewall is 60 percent 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.