Cadillac 2011 STS Owner's Manual page 405

The three digit number indicates
the tire section width in millimeters from sidewall
to sidewall.
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.
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.
Diameter of the wheel in
inches.
represent the load index and speed rating of the
tire. The load index represents the load carrying
capacity a tire is certified to carry. The speed
rating is the maximum speed a tire is certified to
carry a load.
A letter code is used to
These characters
The amount of air inside the tire
pressing outward on each square inch of the tire.
Air pressure is expressed in pounds per square
inch (psi) or kilopascal (kPa).
weight of optional accessories. Some examples of
optional accessories are, automatic transmission,
power steering, power brakes, power windows,
power seats, and air conditioning.
The relationship of a tire's height to
its width.
A rubber coated layer of cords that is
located between the plies and the tread. Cords
may be made from steel or other reinforcing
materials.
The tire bead contains steel wires wrapped
by steel cords that hold the tire onto the rim.
A pneumatic tire in which the plies
are laid at alternate angles less than 90 degrees
to the centerline of the tread.
This means the combined
6-55