The
tire size is written on the tire’s sidewall. Here’s
an example of the way tire sizing looks on the sidewall:
-
P indicates a passenger (car-type) tire. Other
options would be no P indicating metric sizing (essentially the
same as P-sizing, which has its heritage in Europe) or LT for light
truck. LT truck tires are designed for heavier loads and more rugged
service conditions.
- Width
of the tire, in millimeters. The higher the number the wider
the tire.
-
Aspect
ratio - The height of the sidewall section compared to
the width of the tire. Example: If this number was a 50, then the
tire section is half as tall as it is wide. Short sidewalls deliver
crisp handling. Tall sidewalls give a smoother ride. For a specific
tire width, the smaller this number, the shorter the sidewall.
-
Construction
- R indicates radial construction. Unless you specify the other
option, bias (which would have a D [diagonal] or B [belted bias]
in this position instead of an R), you are purchasing a radial tire.
-
Wheel
Size Designation - This indicates the distance across the
“doughnut hole” of a tire, in simple terms. You must
match wheel diameter and tire diameter. For example, a 15-inch diameter
tire must only be mounted on a 15-inch diameter rim. A tire with
a 15 size designation will not work on a 14" wheel, and vice
versa. Improperly matching of wheel and tire size can cause serious
injury or death during installation.
-
Service
Description - Includes the load index (a number) and a
speed symbol (a letter). About load index, remember: Keep the number
the same as or greater than the original tires’ load index.
That number stands for a specific weight-carrying capability. Key
is that the higher the number, the greater load-carrying capacity.
So keep the number the same or higher, because your tires are matched
to the weight of your car. Never choose a tire with a lower load-carrying
capacity than the original equipment tire size.
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